History of radar
Encyclopedia
The history of radar starts with experiments by Heinrich Hertz in the late 19th century that showed that radio waves were reflected by metallic objects. This possibility was suggested in James Clerk Maxwell
's seminal work on electromagnetism
. However, it was not until the early 20th century that systems able to use these principles were becoming widely available, and it was German engineer Christian Huelsmeyer who first used them to build a simple ship detection device intended to help avoid collisions in fog (Reichspatent Nr. 165546). Numerous similar systems were developed over the next two decades.
The name radar
comes from the acronym RADAR, coined in 1940 by the U.S. Navy for public reference to their highly classified work in Radio Detection And Ranging. Thus, a true radar system must both detect and provide range (distance) information for a target. Before 1934, no single system gave this performance; some systems were omni-directional and provided ranging information, while others provided rough directional information but not range. A key development was the use of pulses that were timed to provide ranging, which were sent from large antennas that provided accurate directional information. Combining the two allowed for accurate plotting of targets.
, Great Britain
, Germany
, the USSR, Japan
, the Netherlands
, France
, and Italy
. In addition, Great Britain had shared their basic information with four Commonwealth countries: Australia
, Canada
, New Zealand
, and South Africa
, and these countries had also developed indigenous radar systems. During the war, Hungary
was added to this list.
Progress during the war was rapid and of great importance, probably one of the decisive factors for the victory of the Allies
. By the end of hostilities, the United States, Great Britain, Germany, the USSR, and Japan had a wide diversity of land- and sea-based radars as well as small airborne systems. After the war, radar use was widened to numerous fields including: civil aviation
, marine navigation, radar gun
s for police, meteorology
and even medicine.
But others point out the immense practical consequences of the development of radar. Far more than the atomic bomb, radar contributed to Allied victory in World War II. Robert Buderi states that it was also the precursor of much modern technology. From a review of his book:
Heinrich Hertz (1857–1894) began experimenting with electromagnetic waves in his laboratory. He found that these waves could be transmitted through different types of materials, and were reflected by others, such as conductor
s and dielectric
s. The existence of electromagnetic waves was predicted earlier by the Scottish physicist James Clerk Maxwell
(1831–79), but it was Hertz who first succeeded in generating and detecting what were soon called radio waves
.
(1874–1937). Although he was not the first to "invent" this technology, it might be said that he was the greatest early promoter of practical radio systems and their applications. In a paper read before the Institution of Electrical Engineers in London on March 3, 1899, Marconi described radio beacon experiments he had conducted in Salisbury Plain. Concerning this lecture, in a 1922 paper he wrote:
This paper and a speech presenting the paper to a joint meeting of the Institute of Radio Engineers and the American Institute of Electrical Engineers in New York City on June 20, 1922, is often cited as the seminal event which began widespread interest in the development of radar.
and the Netherlands
of the use of radio echoes
to detect ship
s so that collisions could be avoided. His device consisted of a simple spark gap
used to generate a signal that was aimed using a dipole antenna
with a cylindrical parabolic reflector
. When a signal reflected from a ship was picked up by a similar antenna attached to the separate coherer
receiver
, a bell sounded. During bad weather or fog, the device would be periodically "spun" to check for nearby ships. The apparatus detected presence of ships up to 3 km, and Huelsmeyer planned to extend its capability to 10 km. It did not provide range (distance) information, only warning of a nearby object. He patented the device, called the telemobiloscope, but due to lack of interest by the naval authorities the invention was not put into production.
Huelsmeyer also received a patent amendment for estimating the range to the ship. Using a vertical scan of the horizon with the telemobiloscope mounted on a tower, the operator would find the angle at which the return was the most intense and deduce, by simple triangulation, the approximate distance. This is in contrast to the later development of pulsed radar, which determines distance directly.
(1856–1943) included principles regarding frequency and power levels for primitive radio-location units. In an interview published in The Electrical Experimenter, August 1917, Tesla gave the following:
Tesla also proposed the use of these standing electromagnetic waves
along with pulsed reflected surface wave
s to determine the relative position, speed, and course of a moving object and other modern concepts of radar. Tesla had first proposed that radio location techniques might help find submarine
s (for which it is not well-suited) with a fluorescent screen indicator.
and Leo C. Young
at the U.S. Naval Aircraft Radio Laboratory were conducting communication experiments when they noticed that a wooden ship in the Potomac River
was interfering with their signals; in effect, they had demonstrated the first multistatic radar
, a system that uses separated transmitting and receiving antennas and detects targets due to changes in the signal. In 1930, Lawrence A. Hyland
working with Taylor and Young, now at the U.S. Naval Research Laboratory (NRL) in Washington, D.C., used a similar arrangement of radio equipment to detect a passing aircraft. This led to a proposal by Taylor for using this technique for detecting ships and aircraft.
A simple wave-interference apparatus can detect the presence of an object, but it cannot determine its location
or velocity
. That had to await the invention of pulsed radar, and later, additional encoding techniques to extract this information from a CW signal. When Taylor's group at the NRL were unsuccessful in getting interference radio accepted as a detection means, Young suggested trying pulsing techniques. This would also allow the direct determination of range to the target. The British and the American research groups were independently aware of the advantages of such an approach, but the problem was to develop the timing equipment to make it feasible.
Robert Morris Page
was assigned by Taylor to implement Young's suggestion. Page designed a transmitter operating at 60 MHz and pulsed 10 μs
in duration and 90 μs between pulses. In December 1934, the apparatus was used to detect a plane at a distance of one mile (1.6 km) flying up and down the Potomac. Although the detection range was small and the indications on the oscilloscope monitor were almost indistinct, it demonstrated the basic concept of a pulsed radar system. Based on this, Page, Taylor, and Young are usually credited with building and demonstrating the world’s first true radar.
An important subsequent development by Page was the duplexer, a device that allowed the transmitter and receiver to use the same antenna without over-whelming or destroying the sensitive receiver circuitry. This also solved the problem associated with synchronization of separate transmitter and receiver antennas which is critical to accurate position determination of long-range targets.
The experiments with pulsed radar were continued, primarily in improving the receiver for handling the short pulses. In June 1936, the NRL's first prototype radar system, now operating at 28.6 MHz, was demonstrated to government officials, successfully tracking an aircraft at distances up to 25 miles (40.2 km). Their radar was based on low frequency
signals, at least by today's standards, and thus required large antennas
, making it impractical for ship or aircraft mounting.
Antenna size is inversely proportional to the operating frequency; therefore, the operating frequency of the system was increased to 200 MHz, allowing much smaller antennas. The frequency of 200 MHz was the highest possible with existing transmitter tubes and other components. The new system was successfully tested at the NRL in April 1937, That same month, the first sea-borne testing was conducted. The equipment was temporarily installed on the USS Leary
, with a Yagi antenna
mounted on a gun barrel for sweeping the field of view.
Based on success of the sea trials, the NRL further improved the system. Page developed the ring oscillator
, allowing multiple output tubes and increasing the pulse-power to 15 kW in 5-µs pulses. A 20-by-23 feet (7 m), stacked-dipole “bedspring” antenna was used. In laboratory test during 1938, the system, now designated XAF
, detected planes at ranges up to 100 miles (160.9 km). It was installed on the battleship USS New York for sea trials starting in January 1939, and became the first operational radio detection and ranging set in the U.S. fleet.
In May 1939, a contract was awarded to RCA
for production. Designated CXAM
, deliveries started in May 1940. The acronym RADAR was coined from "Radio Detection And Ranging" as a cover reference to this highly secret technology. One of the first CXAM systems was placed aboard the USS California, a battleship that was sunk in the Japanese attack on Pearl Harbor on December 7, 1941.
started, economic conditions led the U.S. Army Signal Corps to consolidate its widespread laboratory operations to Fort Monmouth, New Jersey. On June 30, 1930, these were designated the Signal Corps Laboratories
(SCL) and Lt. Colonel (Dr.) William R. Blair
was appointed the SCL Director.
Among other activities, the SCL was made responsible for research in the detection of aircraft by acoustical and infrared
radiation means. Blair had performed his doctoral research in the interaction of electromagnet waves with solid materials, and naturally gave attention to this type of detection. Initially, attempts were made to detect infrared
radiation, either from the heat of aircraft engines or as reflected from large searchlights with infrared filters, as well as from radio signals generated by the engine ignition.
Some success was made in the infrared detection, but little was accomplished using radio. In 1932, progress at the Naval Research Laboratory (NRL) on radio interference for aircraft detection was passed on to the Army. While it does not appear that any of this information was used by Blair, the SCL did undertake a systematic survey of what was then known throughout the world about the methods of generating, modulating, and detecting radio signals in the microwave
region.
The SCL's first definitive efforts in radio-based target detection started in 1934 when the Chief of the Army Signal Corps, after seeing a microwave demonstration by RCA
, suggested that radio-echo techniques be investigated. The SCL called this technique radio position-finding (RPF). Based on the previous investigations, the SCL first tried microwaves. During 1934 and 1935, tests of microwave RPF equipment resulted in Doppler-shifted signals being obtained, initially at only a few hundred feet distance and later greater than a mile. These tests involved a bi-static arrangement, with the transmitter at one end of the signal path and the receiver at the other, and the reflecting target passing through or near the path.
Blair was evidently not aware of the success of a pulsed system at the NRL in December 1934. In an internal 1935 note, Blair had commented:
In 1936, W. Delmar Hershberger, SCL’s Chief Engineer at that time, started a modest project in pulsed microwave transmission. Lacking success with microwaves, Hershberger visited the NRL (where he had earlier worked) and saw a demonstration of their pulsed set. Back at the SCL, he and Robert H. Noyes built an experimental apparatus using a 75 watt, 110 MHz (2.73 m) transmitter with pulse modulation and a receiver patterned on the one at the NRL. A request for project funding was turned down by the War Department
, but $75,000 for support was diverted from a previous appropriation for a communication project.
In October 1936, Paul E. Watson
became the SCL Chief Engineer and led the project. A field setup near the coast was made with the transmitter and receiver separated by a mile. On December 14, 1936, the experimental set detected at up to 7 mi (11.3 km) range aircraft flying in and out of New York City
.
Work then began on a prototype system. Ralph I. Cole headed receiver work and William S. Marks lead transmitter improvements. Separate receivers and antennas were used for azimuth and elevation
detection. Both receiving and the transmitting antennas used large arrays of dipole
wires on wooden frames. The system output was intended to aim a searchlight
. The first demonstration of the full set was made on the night of May 26, 1937. A bomber was detected and then illuminated by the searchlight. The observers included the Secretary of War, Henry A. Woodring; he was so impressed that the next day orders were given for the full development of the system. Congress gave an appropriation of $250,000.
The frequency was increased to 200 MHz (1.5 m). The transmitter used 16 tubes in a ring oscillator
circuit (developed at the NRL), producing about 75 kW peak power. Major James C. Moore was assigned to head the complex electrical and mechanical design of lobe switching
antennas. Engineers from Western Electric
and Westinghouse
were brought in to assist in the overall development. Designated SCR-268, a prototype was successfully demonstrated in late 1938 at Fort Monroe
, Virginia. Production of SCR-268 sets was started by Western Electric in 1939, and it entered service in early 1941.
Even before the SCR-268 entered service, it had been greatly improved. In a project led by Major (Dr.) Harold A. Zahl
, two new configurations evolved – the SCR-270 (mobile) and the SCR-271 (fixed-site). Operation at 106 MHz (2.83 m) was selected, and a single water-cooled tube provided 8 kW (100 kW pulsed) output power. Westinghouse received a production contract, and started deliveries near the end of 1940.
The Army deployed five of the first SCR-270 sets around the island of Oahu
in Hawaii
. At 7:02 on the morning of December 7, 1941, one of these radars detected a flight of aircraft at a range of 136 miles (218.9 km) due north. The observation was passed on to an aircraft warning center where it was misidentified as a flight of U.S. bombers known to be approaching from the mainland. The alarm went unheeded, and at 7:48, the Japanese aircraft first struck at Pearl Harbor.
In 1915, Robert Watson Watt
joined the Meteorological Office
as a meteorologist, working at an outstation at Aldershot
in Hampshire
. Over the next 20 years, he studied atmospheric phenomena and developed the use of radio signals generated by lightning
strikes to map out the position of thunderstorm
s. The difficulty in pinpointing the direction of these fleeting signals led to the use of rotatable directional antennas, and in 1923 the use of oscilloscope
s in order to display the signals. An operator would periodically rotate the antenna and look for "spikes" on the oscilloscope to find the direction of a storm. The operation eventually moved to the outskirts of Slough
in Berkshire
, and in 1927 formed the Radio Research Station (RRS), Slough, an entity under the Department of Scientific and Industrial Research
(DSIR). Watson Watt was appointed the RSS Superintendent.
As war clouds gathered over Great Britain, the likelihood of air raids and the threat of invasion by air and sea drove a major effort in applying science and technology to defence. In November 1934, the Air Ministry
established the Committee for Scientific Survey of Air Defence (CSSAD) with the official function of considering "how far recent advances in scientific and technical knowledge can be used to strengthen the present methods of defence against hostile aircraft." Commonly called the “Tizard Committee” after its Chairman, Sir Henry Tizard
, this group had a profound influence on technical developments in Great Britain.
H. E. Wimperis, Director of Scientific Research at the Air Ministry and a member of the Tizard Committee, had read about Nikola Tesla
's claim of inventing a 'death ray
.' Watson Watt, Superintendent of the RSS, Slough, was now well established as an authority in the field of radio, and in January 1935, Wimperis contacted him asking if radio might be used for such a device. After discussing this with his scientific assistant, Arnold F. 'Skip' Wilkins
, Watson Watt wrote back that this was unlikely, but added the following comment: Attention is being turned to the still difficult, but less unpromising, problem of radio detection and numerical considerations on the method of detection by reflected radio waves will be submitted when required.
Over the following several weeks, Wilkins considered the radio detection problem. He outlined an approach and backed it with detailed calculations of necessary transmitter power, reflection characteristics of an aircraft, and needed receiver sensitivity. Watson Watt sent this information to the Air Ministry on February 12, 1935, in a secret report titled "The Detection of Aircraft by Radio Methods."
Reflection of radio signals was critical to the proposed technique, and the Air Ministry asked if this could be proven. To test this, Wilkins set up receiving equipment in a field near Upper Stowe, Northamptonshire
. On February 26, 1935, a Handley Page Heyford
bomber flew along a path between the receiving station and the transmitting towers of a BBC
shortwave
station in nearby Daventry
. The aircraft reflected the 6 MHz (49 m) BBC signal, and this was readily detected by Doppler
-beat interference at ranges up to 8 mi (12.9 km). This convincing test, known as the Daventry Experiment, was witnessed by a representative from the Air Ministry, and led to the immediate authorization to build a full demonstration system.
Based on pulsed transmission as used for probing the ionosphere
. a preliminary system was designed and built at the RRS by the team. Their existing transmitter had a peak power of about 1 kW, and Wilkins had estimated that 100 kW would be needed. Edward George Bowen
was added to the team to design and build such a transmitter. Bowens’ transmitter operated at 6 MHz (50 m), had a pulse-repetition rate of 25 Hz, a pulse width of 25 μs
, and approached the desired power.
Orfordness, a narrow, 19 miles (30.6 km) peninsula
in Suffolk
along the coast of the North Sea
, was selected as the test site. Here the equipment would be openly operated in the guise of an ionospheric monitoring station. In mid-May, 1935, the equipment was moved to Orfordness. Six wooden towers were erected, two for stringing the transmitting antenna, and four for corners of crossed receiving antennas. In June, general testing of the equipment began.
On June 17, the first target was detected—a Supermarine Scapa
flying boat at 17 mi (27.4 km) range. It is historically correct that on June 17, 1935, radio-based detection and ranging was first demonstrated in Great Britain. Watson Watt, Wilkins, and Bowen are generally credited with initiating what would later be called radar in this nation.
In December 1935, the British Treasury appropriated £60,000 for a five-station system called Chain Home
(CH), covering approaches to the Thames Estuary
. The secretary of the Tizard Committee, Albert Percival Rowe, coined the acronym RDF as a cover for the work, meaning Range and Direction Finding but suggesting the already well-known Radio Direction Finding
.
In 1940 John Randall (physicist)
and Harry Boot
developed the Cavity magnetron
which made one centimeter radar a reality. This device, the size of a small dinner plate, could be carried easily on aircraft and the short wavelength meant that the antenna would also be small and hence suitable for mounting on aircraft. The short wavelength and high power made it very effective at spotting submarines from the air.
, nearby on the mainland. Until this time, the work had officially still been under the DSIR, but was now transferred to the Air Ministry. At the new Bawdsey Research Station, the CH equipment was assembled as a prototype. There were equipment problems when the Royal Air Force
(RAF) first exercised the prototype station in September 1936. These were cleared by the next April, and the Air Ministry started plans for a larger network of stations.
Initial hardware at CH stations was as follows: The transmitter operated on four pre-selected frequencies between 20 and 55 MHz, adjustable within 15 seconds, and delivered a peak power of 200 kW. The pulse duration was adjustable between 5 to 25 μs, with a repetition rate selectable as either 25 or 50 Hz. For synchronization of all CH transmitters, the pulse generator was locked to the 50 Hz of the British power grid. Four 360 feet (109.7 m) steel towers supported transmitting antennas, and four 240 feet (73.2 m) wooden towers supported cross-dipole arrays at three different levels. A goniometer
was used to improve the directional accuracy from the multiple receiving antennas.
By the summer of 1937, 20 initial CH stations were in check-out operation. A major RAF exercise was performed before the end of the year, and was such a success that £10,000,000 was appropriated by the Treasury for an eventual full chain of coastal stations. At the start of 1938, the RAF took over control of all CH stations, and the network began regular operations.
In May 1938, Rowe replaced Watson Watt as Superintendent at Bawdsey. In addition to the work on CH and successor systems, there was now major work in airborne RDF equipment. This was led by E. G. Bowen and centered on 200-MHz (1.5 m) sets. The higher frequency allowed smaller antennas, appropriate for aircraft installation.
From the initiation of RDF work at Orfordness, the Air Ministry had kept the British Army and the Royal Navy generally informed; this led to both of these forces having their own RDF developments.
and P. E. Pollard had examined pulsed 600 MHz (50-cm) signals for detection of ships. Although they prepared a memorandum on this subject and performed preliminary experiments, for undefined reasons the War Office did not give it consideration.
As the Air Ministry’s work on RDF progressed, Colonel Peter Worlledge of the Royal Engineer and Signals Board met with Watson Watt and was briefed on the RDF equipment and techniques being developed at Orfordness. His report, “The Proposed Method of Aeroplane Detection and Its Prospects,” led the SEE to set up an “Army Cell” at Bawdsey in October 1936. This was under E. Talbot Paris and the staff included Butement and Pollard. The Cell’s work emphasize two general types of RDF equipment: gun-laying (GL) systems for assisting anti-aircraft guns and searchlights, and coastal- defense (CD) systems for directing coastal artillery and defense of Army bases overseas.
Pollard led the first project, a gun-laying RDF code-named Mobile Radio Unit (MRU). This truck-mounted system was designed a small version of a CH station. It operated at 23 MHz (13 m) with a power of 300 kW. A single 105 feet (32 m) tower supported a transmitting antenna, as well as two receiving antennas set orthogonally for estimating the signal bearing. In February 1937, a developmental unit detected an aircraft at 60 m (96 km) range. The Air Ministry also adopted this system as a mobile auxiliary to the CH system.
In early 1938, Butement started the development of a CD system based on Bowen’s evolving 200-MHz (1.5-m) airborne sets. The transmitter had a 400 Hz pulse rate, a 2-μs pulse width, and 50 kW power (later increased to 150 kW). Although many of Bowen’s transmitter and receiver components were used, the system would not be airborne so there were no limitations on antenna size.
Primary credit for introducing beamed RDF systems in Great Britain must be given to Butement. For the CD, he developed a large dipole array, 10 feet (3 m) high and 24 feet (7.3 m) wide, giving much narrower beams and higher gain. This could be rotated at a speed up to 1.5 revolutions per minute. For greater directional accuracy, lobe switching
on the receiving antennas was adopted. As a part of this development, he formulated the first – at least in Great Britain – mathematical relationship that would later become well known as the “radar range equation.”
By May 1939, the CD RDF could detect aircraft flying as low as 500 feet (152.4 m) and at a range of 25 mi (40.2 km). With an antenna 60 feet (18.3 m) above sea level, it could determine the range of a 2,000-ton ship at 24 mi (38.6 km) and with an angular accuracy of as little as a quarter of a degree.
, Hampshire
, on the south coast.
The HMSS started RDF work in September 1935. Initial efforts, under R. F. Yeo, were in wavelengths ranging between 75 MHz (4 m) and 1.2 GHz (25 cm). All of the work was under the utmost secrecy; it could not even be discussed with other scientists and engineers at Portsmouth. A 75 MHz range-only set was eventually developed and designated Type 79X. Basic tests were done using a training ship, but the operation was unsatisfactory.
In August 1937, the RDF development at the HMSS changed, with many of their best researchers brought into the activity. John D. S. Rawlinson was made responsible for improving the Type 79X. To increase the efficiency, he decreased the frequency to 43 MHz (7 m). Designated Type 79Y, it had separate, stationary transmitting and receiving antennas.
Prototypes of the Type 79Y air-warning system were successfully tested at sea in early 1938. The detection range on aircraft was between 30 and 50 mi (48 and 80 km), depending on height. The systems were then placed into service in August on the cruiser HMS Sheffield
and in October on the battleship HMS Rodney. These were the first vessels in the Royal Navy with RDF systems.
Over the following three decades in invention-rich Germany, a number of radio-based detection systems were developed, but none were true radars. This situation changed as World War II loomed closer. Developments in three leading industries are described.
, Scientific Director at the Kriegsmarine
(German Navy) Nachrichtenmittel-Versuchsanstalt (NVA—Experimental Institute of Communication Systems) in Kiel
, was attempting to improve the acoustical methods of underwater detection of ships. He concluded that the desired accuracy in measuring distance to targets could be attained only by using pulsed electromagnetic waves.
During 1933, Kühnhold first attempted to test this concept with a transmitting and receiving set that operated in the microwave
region at 13.5 cm (2.22 GHz). The transmitter used a Barkhausen-Kurz tube
(the first microwave generator) that produced only 0.1 watt. Unsuccessful with this, he asked for assistance from Paul-Gunther Erbslöh and Hans-Karl Freiherr von Willisen, amateur radio operators who were developing a VHF system for communications. They enthusiastically agreed, and in January 1934, formed a company, Gesellschaft für Elektroakustische und Mechanische Apparate ((GEMA)), for the effort. From the start, the firm was always called simply GEMA.
Work on a Funkmessgerät für Untersuchung (radio measuring device for reconnaissance) began in earnest at GEMA. Hans Hollmann
and Theodor Schultes, both affiliated with the prestigious Heinrich Hertz Institute in Berlin
, were added as consultants. The first apparatus used a split-anode magnetron purchased from Philips
in the Netherlands
. This provided about 70 W at 50 cm (600 MHz), but suffered from frequency instability. Hollmann built a regenerative
receiver and Schultes developed Yagi antenna
s for transmitting and receiving. In June 1934, large vessels passing through the Kiev Harbor were detected by Doppler-beat interference at a distance of about 2 km (1.2 mi). In October, strong reflections were observed from an aircraft that happened to fly through the beam; this opened consideration of targets other than ships.
Kühnhold then shifted the GEMA work to a pulse-modulated system. A new 50 cm (600 MHz) Philips magnetron with better frequency stability was used. It was modulated with 2- μs
pulses at a PRF of 2000 Hz. The transmitting antenna was an array of 10 pairs of dipoles with a reflecting mesh. The wide-band regenerative receiver used Acorn tubes from RCA, and the receiving antenna had three pairs of dipoles and incorporated lobe switching
. A blocking device (a duplexer), shut the receiver input when the transmitter pulsed. A Braun tube (a CRT) was used for displaying the range.
The equipment was first tested at a NVA site at the Lübecker Bay near Pelzerhaken. During May 1935, it detected returns from woods across the bay at a range of 15 km (9.3 mi). It had limited success, however, in detecting a research ship, Welle, only a short distance away. The receiver was then rebuilt, becoming a super-regenerative set with two intermediate-frequency stages. With this improved receiver, the system readily tracked vessels at up to 8 km (5 mi) range.
In September 1935, a demonstration was given to the Commander-in-Chief of the Kriegsmarine. The system performance was excellent; the range was read off the Braun tube with a tolerance of 50 meters (less than 1 percent variance), and the lobe switching allowed a directional accuracy of 0.1 degree. Historically, this marked the first naval vessel equipped with radar. Although this apparatus was not put into production, GEMA was funded to develop similar systems operating around 50 cm (500 MHz). These became the Seetakt for the Kriegsmarine and the Freya
for the Luftwaffe (German Air Force).
Kühnhold remained with the NVA but also consulted with GEMA. He is considered by many in Germany as the Father of Radar. During 1933-6, Hollmann wrote the first comprehensive treatise on microwaves, Physik und Technik der ultrakurzen Wellen (Physics and Technique of Ultrashort Waves), Springer 1938.
on microwave tubes. (Telefunken was the largest supplier of radio products in Germany) There, Wilhelm Tolmé Runge
had told him that no vacuum tubes were available for these frequencies. In fact, Runge was already experimenting with high-frequency transmitters and had Telefunken’s tube department working on cm-wavelength devices.
In the summer of 1935, Runge, now Director of Telefunken’s Radio Research Laboratory, initiated an internally funded project in radio-based detection. Using Barkhausen-Kurz tubes, a 50 cm (600 MHz) receiver and 0.5-W transmitter were built. With the antennas placed flat on the ground some distance apart, Runge arranged for an aircraft to fly overhead and found that the receiver gave a strong Doppler-beat interference signal.
Runge, now with Hans Hollmann as a consultant, continued in developing a 1.8 m (170 MHz) system using pulse-modulation. Wilhelm Stepp developed a transmit-receive device (a duplexer) for allowing a common antenna. Stepp also code-named the system Darmstadt after his home town, starting the practice in Telefunken of giving the systems names of cities. The system, with only a few watts transmitter power, was first tested in February 1936, detecting an aircraft at about 5 km (3.1 mi) distance. This led the Luftwaffe to fund the development of a 50 cm (600 MHz) gun-laying system, the Würzburg.
In early 1936, initial experiments gave reflections from large buildings at up to about 7 km (4.3 mi). The power was doubled by using two tubes, and in mid-1936, the equipment was set up on cliffs near Kiel, and good detections of ships at 7 km (4.3 mi) and aircraft at 4 km (2.5 mi) were attained.
The success of this experimental set was reported to the Kriegsmarine, but they showed no interest; they were already fully engaged with GEMA for similar equipment. Also, because of extensive agreements between Lorenz and many foreign countries, the naval authorities had reservations concerning the company handling classified work. The DFA was then demonstrated to the Heer (German Army), and they contracted with Lorenz for developing Kurfürst (Cure prince), a system for supporting Flugzeugabwehrkanone (Flak, anti-aircraft guns).
, a physics instructor at the Imperial Russian Navy
school in Kronstadt
, developed an apparatus using a coherer
tube for detecting distant lightning strikes. The next year, he added a spark-gap transmitter
and demonstrated the first radio communication set in Russia
. During 1897, while testing this in communicating between two ships in the Baltic Sea
, he took note of an interference beat caused by the passage of a third vessel. In his report, Popov wrote that this phenomenon might be used for detecting objects, but he did nothing more with this observation.
In a few years following the 1917 Russian Revolution and the establishment the Union of Soviet Socialist Republics (USSR or Soviet Union) in 1924, Germany’s Luftwaffe
had aircraft capable of penetrating deep into Soviet territory. Thus, the detection of aircraft at night or above clouds was of great interest to the Voiska Protivo-vozdushnoi aborony (PVO, Air Defense Forces) of the Raboche-Krest'yanskaya Krasnaya Armiya (RKKA, Workers’–Peasants’ Red Army
).
The PVO depended on optical devices for locating targets, and had physicist Pavel K. Oshchepkov
conducting research in possible improvement of these devices. In June 1933, Oshchepkov changed his research from optics to radio techniques and started the development of a razvedyvlatl’naya elektromagnitnaya stantsiya (reconnaissance electromagnetic station). In a short time, Oshchepkov was made responsible for a PVO experino-tekknicheskii sektor (technical expertise sector) devoted to radiolokatory (radio-location) techniques as well as heading a Special Construction Bureau (SCB) in Leningrad
(formerly St. Petersberg).
After examining existing optical and acoustical equipment, Lobanov also turned to radio-location techniques. For this he approached the Tsentral’naya radiolaboratoriya (TsRL, Central Radio Laboratory) in Leningrad. Here, Yu. K. Korovin was conducting research on VHF communications, and had built a 50 cm (600 MHz), 0.2 W transmitter using a Barkhausen-Kurz tube
. For testing the concept, Korovin arranged the transmitting and receiving antennas along the flight path of an aircraft. On January 3, 1934, a Doppler
signal was received by reflections from the aircraft at some 600 m range and 100–150 m altitude.
For further research in detection methods, a major conference on this subject was arranged for the PVO by the Rossiiskaya Akademiya Nauk (RAN, Russian Academy of Sciences
). The conference was held in Leningrad in mid-January, 1934, and chaired by Abram Fedorovich Ioffe, Director of the Leningrad Physical-Technical Institute (LPTI). Ioffe was generally considered the top Russian physicist of his time. All types of detection techniques were discussed, but radio-location received the greatest attention.
To distribute the conference findings to a wider audience, the proceedings were published the following month in a journal. This included all of the then-existing information on radio-location in the USSR, available (in Russian language) to researchers in this field throughout the world.
Recognizing the potential value of radio-location to the military, the GAU made a separate agreement with the Leningrad Electro-Physics Institute (LEPI), for a radio-location system. This technical effort was led by B. K. Shembel. The LEPI had built a transmitter and receiver to study the radio-reflection characteristics of various materials and targets. Shemlbel readily made this into an experimental bi-static
radio-location system called Bistro (Rapid).
The Bistro transmitter, operating at 4.7 m (64 MHz), produced near 200 W and was frequency-modulated by a 1 kHz tone. A fixed transmitting antenna gave a broad coverage of what was called a radiozkzn (radio screen). A regenerative
receiver, located some distance from the transmitter, had a dipole antenna mounted on a hand-driven reciprocating mechanism. An aircraft passing into the screened zone would reflect the radiation, and the receiver would detect the Doppler-interference beat between the transmitted and reflected signals.
Bistro was first tested during the summer of 1934. With the receiver up to 11 km away from the transmitter, the set could only detect an aircraft entering a screen at about 3 km (1.9 mi) range and a under 1,000 m. With improvements, it was believed to have a potential range of 75 km, and five sets were ordered in October for field trials. Bistro is often cited as the USSR’s first radar system; however, it was incapable of directly measuring range and thus could not be so classified.
LEPI and TsRL were both made a part of Nauchno-issledovatel institut-9 (NII-9, Scientific Research Institute #9), a new GAU organization opened in Leningrad in 1935. Mikhail A. Bonch-Bruyevich, a renowned radio physicist previously with TsRL and the University of Leningrad, was named the NII-9 Scientific Director.
Research on magnetrons began at Kharkov University in Ukraine
during the mid-1920s. Before the end of the decade this had resulted in publications with worldwide distribution, such as the German journal Annalen der Physik
(Annals of Physics). Based on this work, Ioffe recommended that a portion of the LEPI be transferred to the city of Kharkov, resulting in the Ukrainian Institute of Physics and Technology (LIPT) being formed in 1930. Within the LIPT, the Laboratory of Electromagnetic Oscillations (LEMO), headed by Abram A. Slutskin
, continued with magnetron development. Led by Aleksandr S. Usikov, a number of advanced segmented-anode magnetrons evolved. (It is noted that these and other early magnetrons developed in the USSR suffered from frequency instability, a problem in their use in Soviet radar systems.)
In 1936, one of Usikov’s magnetrons producing about 7 W at 18 cm (1.7 GHz) was used by Shembel at the NII-9 as a transmitter in a radioiskatel (radio-seeker) called Burya (Storm). Operating similarly to Bistro, the range of detection was about 10 km, and provided azimuth and elevation coordinates estimated to within 4 degrees. No attempts were made to make this intro a pulsed system, thus, it could not provide range and was not qualified to be classified as a radar. It was, however, the first microwave radio-detection system.
While work by Shembel and Bonch-Bruyevich on continuous-wave systems was taking place at NII-9, Oshehepkov at the SCB and V. V. Tsimbalin of Ioffe’s LPTI were pursuing a pulsed system. In 1936, they built a radio-location set operating at 4 m (75 MHz) with a peak-power of about 500 W and a 10-μs pulse duration. Before the end of the year, tests using separated transmitting and receiving sites resulted in an aircraft being detected at 7 km. In April 1937, with the peak-pulse power increased to 1 kW and the antenna separation also increased, test showed a detection range of near 17 km at a height of 1.5 km. Although a pulsed system, it was not capable of directly providing range – the technique of using pulses for determining range had not yet been developed.
of dictator Joseph Stalin
swept over the military high commands and its supporting scientific community. The PVO chief was executed. Oshchepkov, charged with “high crime,” was sentenced to 10 years at a Gulag
penal labor camp. NII-9 as an organization was saved, but Shenbel was dismissed and Bonch-Bruyevich was named the new director.
The Nauchnoissledovatel skii ispytalel nyi institut suyazi RKKA (NIIIS-KA, Scientific Research Institute of Signals of the Red Army), had initially opposed research in radio-location, favoring instead acoustical techniques. However, this portion of the Red Army gained power as a result of the Great Purge, and did an about face, pressing hard for speedy development of radio-location systems. They took over Oshchepkov’s laboratory and were made responsible for all existing and future agreements for research and factory production.
Writing later about the Purge and subsequent effects, General Lobanov commented that it led to the development being placed under a single organization, and the rapid reorganization of the work to accomplish needed results.
At Oshchepkov’s former laboratory, work with the 4 m (75 MHz) pulsed-transmission system was continued by A. I. Shestako. Through pulsing, the transmitter produced a peak power of 1 kW, the highest level thus far generated. In July 1938, a fixed-position, bi-static experimental system detected an aircraft at about 30 km range at heights of 500 m, and at 95 km range, for high-flying targets at 7.5 km altitude. The system was still incapable of directly determining the range.
The project was then taken up by Ioffe’s LPTI, resulting in the development of a mobile system designated Redut (Redoubt). An arrangement of new transmitter tubes was used, giving near 50 kW peak-power with a 10 μs pulse-duration. Yagi
antennas were adopted for both transmitting and receiving.
The Redut was first field tested in October 1939, at a site near Sevastopol
, a port in Ukraine on the coast of the Black Sea
. This testing was in part to show the NKKF (Soviet Navy) the value of early-warning radio-location for protecting strategic ports. With the equipment on a cliff about 160 meters above sea level, a flying boat was detected at ranges up to 150 km. The Yagi antennas were spaced about 1,000 meters; thus, close coordination was required to aim them in synchronization.
At the NII-9 under Bonch-Bruyevich, scientists developed two types of very advanced microwave generators. In 1938, a linear-beam, velocity-modulated vacuum tube (a klystron
) was developed by Nikolay Devyatkov
, based on designs from Kharkpv. This device produced about 25 W at 15–18 cm (2.0–1.7 GHz) and was later used in experimental systems. Devyatkov followed this with a simpler, single-resonator device (a reflex klystron). At this same time, D. E. Malyarov and N. F. Alekseyev were building a series of magnetrons, also based on designs from Kharkov; the best of these produced 300 W at 9 cm (3 GHz).
Also at NII-9, D. S. Stogov was placed in charge of the improvements to the Bistro system. Redesignated as Reven (Rhubarb), it was tested in August 1938, but was only marginally better than the predecessor. With additional minor operational improvements, it was made into a mobile system called Radio Ulavlivatel Samoletov (RUS, Radio Catcher of Aircraft), soon designated as RUS-1. This continuous-wave, bi-static system had a truck-mounted transmitter operating at 4.7 m (64 MHz) and two truck-mounted receivers.
Although the RUS-1 transmitter was in a cabin on the rear of a truck, the antenna had to be strung between external poles anchored to the ground. A second truck carrying the electrical generator and other equipment was backed against the transmitter truck. Two receivers were used, each in a truck-mounted cabin with a dipole antenna on a rotatable pole extended overhead. In use, the receiver trucks were placed about 40 km apart; thus, with two positions, it would be possible to make a rough estimate of the range by triangulation
on a map.
The RUS-1 system was tested and put into production in 1939, then entered service in 1940, becoming the first deployed radio-location system in the Red Army. A total of about 45 RUS-1 systems were built at the Svetlana Factory in Leningrad before the end of 1941, and deployed along the western USSR borders and in the Far East. Without direct ranging capability, however, the military found the RUS-1 to be of little value.
Even before the demise of efforts in Leningrad, the NIIIS-KA had contracted with the UIPT in Kharkov to investigate a pulsed radio-location system for anti-aircraft applications. This led the LEMO, in March 1937, to start an internally funded project with the code name Zenit (a popular football team at the time). The transmitter development was led by Usikov, supplier of the magnetron used earlier in the Burya. For the Zenit, Usikov used a 60 cm (500 MHz) magnetron pulsed at 10–20 μs duration and providing 3 kW pulsed power, later increased to near 10 kW. Semion Braude
led the development of a superheterodyne receiver
using a tunable magnetron as the local oscillator
. The system had separate transmitting and receiving antennas set about 65 m apart, built with dipoles backed by 3-meter parabolic reflectors.
Zenit was first tested in October 1938. In this, a medium-sized bomber was detected at a range of 3 km. The testing was observed by the NIIIS-KA and found to be sufficient for starting a contracted effort. An agreement was made in May 1939, specifying the required performance and calling for the system to be ready for production by 1941. The transmitter was increased in power, the antennas had selsens added to allow them to track, and the receiver sensitivity was improved by using an RCA
955 acorn triode as the local oscillator.
A demonstration of the improved Zenit was given in September 1940. In this, it was shown that the range, altitude, and azimuth of an aircraft flying at heights between 4,000 and 7,000 meters could be determined at up to 25 km distance. The time required for these measurements, however, was about 38 seconds, far too long for use by anti-aircraft batteries. Also, with the antennas aimed at a low angle, there was a dead zone of some distance caused by interference from ground-level reflections. While this performance was not satisfactory for immediate gun-laying applications, it was the first full three-coordinate radio-location system in the Soviet Union and showed the way for future systems.
Work at the LEMO continued on Zenit, particularly in converting it into a single-antenna system designated Rubin. This effort, however, was disrupted by the invasion of the USSR by Germany in June 1941. In a short while, the development activities at Kharkov were ordered to be evacuated into the Far East. The research efforts in Leningrad were similarly dispersed.
After eight years of effort by highly qualified physicists and engineers, the USSR entered World War II without a fully developed and fielded radar system.
in warfare at sea was by the Imperial Japanese Navy
, in defeating the Russian Imperial Fleet in 1904. There was an early interest in equipment for radio direction-finding, for use in both navigation and military surveillance. The Imperial Navy developed an excellent receiver for this purpose in 1921, and soon most of the Japanese warships had this equipment.
In the two decades between the two World Wars, radio technology in Japan made advancements on a par with that in the western nations. There were often impediments, however, in transferring these advancements into the military. For a long time, the Japanese had believed they had the best fighting capability of any military force in the world. The military leaders, who were then also in control of the government, sincerely felt that the weapons, aircraft, and ships that they had built were fully sufficient and, with these as they were, the Japanese Army and Navy were invincible. In 1936, Japan joined Nazi Germany
and Fascist Italy
in a Tripartite Pact
.
The academic research tended toward the improvement of basic technologies, rather than their specific applications. There was considerable research in high-frequency and high-power oscillators, such as the magnetron
, but the application of these devices was generally left to industrial and military researchers.
One of Japan’s best-known radio researchers in the 1920s-30s era was Professor Hidetsugu Yagi
. After graduate study in Germany, England, and America, Yagi joined Tohoku University where his research centered on antennas and oscillators for high-frequency communications. A summary of the radio research work at Tohoku University was contained in a 1928 seminal paper by Yagi.
Jointly with Shintaro Uda
, one Yagi’s first doctoral students, a radically new antenna emerged. It had a number of parasitic elements (directors and reflectors) and would come to be known as the Yagi-Uda or Yagi antenna
. A U.S. patent, issued in May 1932, was assigned to RCA
. To this day, this is the most widely used directional antenna
worldwide.
The cavity magnetron
was also of interest to Yagi. This HF
(~10-MHz) device had been invented in 1921 by Albert W. Hull at General Electric
, and Yagi was convinced that it could function in the VHF or even the UHF region. In 1927, Kinjiro Okabe
, another of Yagi’s early doctoral students, developed a split-anode device that ultimately generated oscillations at wavelengths down to about 12 cm (2.5 GHz).
Researchers at other Japanese universities and institutions also started projects in magnetron development, leading to improvements in the split-anode device. These included Kiyoshi Morita at the Tokyo Institute of Technology
, and Tsuneo Ito at Tokoku University.
Shigeru Nakajima at Japan Radio Company
(JRC) saw a commercial potential of these devices and began the further development and subsequent very profitable production of magnetrons for the medical dielectric heating
(diathermy) market. The only military interest in magnetrons was shown by Yoji Ito
at the Naval Technical Research Institute (NTRI).
The NTRI was formed in 1922, and became fully operational in 1930. Located at Meguro, Tokyo
, near the Tokyo Institute of Technology, first-rate scientists, engineers, and technicians were engaged in activities ranging from designing giant submarines to building new radio tubes. Included were all of the precursors of radar, but this did not mean that the heads of the Imperial Navy accepted these accomplishments.
In 1936, Tsuneo Ito (no relationship to Yoji Ito) developed an 8-split-anode magnetron that produced about 10 W at 10 cm (3 GHz). Based on its appearance, it was named Tachibana (or Mandarin, an orange citrus fruit). Tsuneo Ito also joined the NTRI and continued his research on magnetrons in association with Yoji Ito. In 1937, they developed the technique of coupling adjacent segments (called push-pull), resulting in frequency stability, an extremely important magnetron breakthrough.
By early 1939, NTRI/JRC had jointly developed a 10-cm (3-GHz), stable-frequency Mandarin-type magnetron (No. M3) that, with water cooling, could produce 500-W power. In the same time period, magnetrons were built with 10 and 12 cavities operating as low as 0.7 cm (40 GHz). The configuration of the M3 magnetron was essentially the same as that used later in the magnetron developed by Boot and Randall
at Birmingham University in early 1940, including the improvement of strapped cavities. Unlike the high-power magnetron in Great Britain, however, the initial device from the NTRI generated only a few hundred watts.
In general, there was no lack of scientific and engineering capabilities in Japan; their warships and aircraft clearly showed high levels of technical competency. They were ahead of Great Britain in the development of magnetrons, and their Yagi antenna was the world standard for VHF systems. It was simply that the top military leaders failed to recognize how the application of radio in detection and ranging – what was often called the Radio Range Finder (RRF) – could be of value, particularly in any offensive role; offense not defense, totally dominated their thinking.
) were making coverage tests on high-frequency transmitters when rapid fading of the signal was observed. This occurred whenever an aircraft passed over the line between the transmitter and receiving meter. Masatsugu Kobayashi, the Manager of NEC’s Tube Department, recognized that this was due to the beat-frequency interference of the direct signal and the Doppler-shifted signal reflected from the aircraft.
Kobayashi suggested to the Army Science Research Institute that this phenomenon might be used as an aircraft warning method. Although the Army had rejected earlier proposals for using radio-detection techniques, this one had appeal because it was based on an easily understandable method and would require little developmental cost and risk to prove its military value. NEC assigned Kinji Satake of their Research Institute to develop a system called the Bi-static Doppler Interference Detector (BDID).
For testing the prototype system, it was set up on an area recently occupied by Japan along the coast of China. The system operated between 4.0-7.5 MHz (75–40 m) and involved a number of widely spaced stations; this formed a radio screen that could detect the presence (but nothing more) of an aircraft at distances up to 500 km (310.7 mi). The BDID was the Imperial Army’s first deployed radio-based detection system, placed into operation in early 1941.
A similar system was developed by Satake for the Japanese homeland. Information centers received oral warnings from the operators at BDID stations, usually spaced between 65 and 240 km (40 and 150 mi). To reduce homing vulnerability – a great fear of the military – the transmitters operated with only a few watts power. Although originally intended to be temporary until better systems were available, they remained in operation throughout the war. It was not until after the start of war the Imperial Army had equipment that could be called radar.
Funding was provided to the Osaka Laboratory for experimental investigation of this technique. Kinjiro Okabe, the inventor of the split-anode magnetron and who had followed Yagi to Osaka, led the effort. Theoretical analyses indicated that the reflections would be greater if the wavelength was approximately the same as the size of aircraft structures. Thus, a VHF transmitter and receiver with Yagi antennas separated some distance were used for the experiment.
In 1936, Okabe successfully detected a passing aircraft by the Doppler-interference method; this was the first recorded demonstration in Japan of aircraft detection by radio. With this success, Okabe’s research interest switched from magnetrons to VHF equipment for target detection. This, however, did not lead to any significant funding. The top levels of the Imperial Navy believed that any advantage of using radio for this purpose were greatly outweighed by enemy intercept and disclosure of the sender’s presence.
Historically, warships in formation used lights and horns to avoid collision at night or when in fog. Newer techniques of VHF radio communications and direction-finding might also be used, but all of these methods were highly vulnerable to enemy interception. At the NTRI, Yoji Ito proposed that the UHF signal from a magnetron might be used to generate a very narrow beam that would have a greatly reduced chance of enemy detection.
Development of microwave system for collision avoidance started in 1939, when funding was provided by the Imperial Navy to JRC for preliminary experiments. In a cooperative effort involving Yoji Ito of the NTRI and Shigeru Nakajima of JRC, an apparatus using a 3-cm (10-GHz) magnetron with frequency modulation was designed and built. The equipment was used in an attempt to detect reflections from tall structures a few kilometers away. This experiment gave poor results, attributed to the very low power from the magnetron.
The initial magnetron was replaced by one operating at 16 cm (1.9 GHz) and with considerably higher power. The results were then much better, and in October 1940, the equipment obtained clear echoes from a ship in Tokyo Bay
at a distance of about 10 km (6.2 mi). There was still no commitment by top Japanese naval officials for using this technology aboard warships. Nothing more was done at this time, but late in 1941, the system was adopted for limited use.
In late 1940, Japan arranged for two technical missions to visit Germany and exchange information about their developments in military technology. Commander Yoji Ito represented the Navy’s interest in radio applications, and Lieutenant Colonel Kinji Satake did the same for the Army. During a visit of several months, they exchanged significant general information, as well as limited secret materials in some technologies, but little directly concerning radio-detection techniques. Neither side even mentioned magnetrons, but the Germans did apparently disclose their use of pulsed techniques.
After receiving the reports from the technical exchange in Germany, as well as intelligence reports concerning the success of Great Britain with firing using RDF, the Naval General Staff reversed itself and tentatively accepted pulse-transmission technology. On August 2, 1941, even before Yoji Ito returned to Japan, funds were allocated for the initial development of pulse-modulated radars. Commander Chuji Hashimoto of the NTRI was responsible for initiating this activity.
A prototype set operating at 4.2 m (71 MHz) and producing about 5 kW was completed on a crash basis. With the NTRI in the lead, the firm NEC and the Research Laboratory of Japan Broadcasting Corporation (NHK
) made major contributions to the effort. Kenjiro Takayanagi
, Chief Engineer of NHK’s experimental television station and called “the father of Japanese television,” was especially helpful in rapidly developing the pulse-forming and timing circuits, as well as the receiver display. In early September 1941, the prototype set was first tested; it detected a single bomber at 97 km (60.3 mi) and a flight of aircraft at 145 km (90.1 mi).
The system, Japan’s first full Radio Range Finder (RRF – radar), was designated Mark 1 Model 1. Contracts were given to three firms for serial production; NEC built the transmitters and pulse modulators, Japan Victor the receivers and associated displays, and Fuji Electrical the antennas and their servo drives. The system operated at 3.0 m (100 MHz) with a peak-power of 40 kW. Dipole arrays with matte+-type reflectors were used in separate antennas for transmitting and receiving.
In November 1941, the first manufactured RRF was placed into service as a land-based early-warning system at Katsuura, Chiba
, a town on the Pacific coast about 100 km (62.1 mi) from Tokyo. A large system, it weighed close to 8,700 kg (19,000 lb). The detection range was about 130 km (80.8 mi) for single aircraft and 250 km (155.3 mi) for groups.
were along two independent lines: one a microwaves system at the firm Philips and the other a VHF system at a laboratory of the Armed Forces.
The Philips
Company in Eindhoven, Netherlands
, operated Natuurkundig Laboratorium (NatLab) for fundamental research related to its products. NatLab researcher Klass Posthumus developed a magnetron split into four elements.
In developing a communication system using this magnetron, C.H.J.A. Stall was testing the transmission by using parabolic
transmitting and receiving antennas set side-by-side, both aimed at a large plate some distance away. To overcome frequency instability of the magnetron, pulse modulation was used. It was found that the plate reflected a strong signal.
Recognizing the potential importance of this as a detection device, NatLab arranged a demonstration for the Koninklijke Marine (Royal Netherlands Navy
). This was conducted in 1937 across the entrance to the main naval port at Marsdiep
. Reflections from sea waves obscured the return from the target ship, but the Navy was sufficiently impressed to initiate sponsorship of the research. In 1939, an improved set was demonstrated at Wijk aan Zee, detecting a vessel at a distance of 3.2 km (2 mi).
A prototype system was built by Philips, and plans were started by the firm Nederlandse Seintoestellen Fabriek (a Philips subsidiary) for building a chain of warning stations to protect the primary ports. Some field testing of the prototype was conducted, but the project was discontinued when Germany invaded the Netherlands on May 10, 1940. Within the NatLab, however, the work was continued in great secrecy until 1942.
During the early 1930s, there were widespread rumours of a “death ray” being developed. The Dutch Parliament set up a Committee for the Applications of Physics in Weaponry under G.J. Elias to examine this potential, but the Committee quickly discounted death rays. The Committee did, however, establish the Laboratorium voor Fysieke Ontwikkeling (LFO, Laboratory for Physical Development), dedicated to supporting the Netherlands Armed Forces.
Operating in great secrecy, the LFO opened a facility called the Meetgebouw (Measurements Building) located on the Plain of Waalsdorp. In 1934, J.L.W.C. von Weiler joined the LFO and, with S.G. Gratama, began research on a 1.25-m (240-MHz) communication system to be used in artillery spotting.
In 1937, while tests were being conducted on this system, a passing flock of birds disturbed the signal. Realizing that this might be a potential method for detecting aircraft, the Minister of War ordered continuation of the experiments. Weiler and Gratama set about developing a system for directing searchlights and aiming anti-aircraft guns.
The experimental “electrical listening device” operated at 70 cm (430 MHz) and used pulsed transmission at an RPF of 10 kHz. A transmit-receive blocking circuit was developed to allow a common antenna. The received signal was displayed on a CR tube with a circular time base. This set was demonstrated to the Army in April 1938 and detected an aircraft at a range of 18 km (11.2 mi). The set was rejected, however, because it could not withstand the harsh environment of Army combat conditions.
The Navy was more receptive. Funding was provided for final development, and Max Staal was added to the team. To maintain secrecy, they divided the development into parts. The transmitter was built at the Delft Technical College
and the receiver at the University of Leiden. Ten sets would be assembled under the personal supervision of J.J.A. Schagen van Leeuwen, head of the firm Hazemeijer Fabriek van Signaalapparaten.
The prototype had a peak-power of 1 kW, and used a pulse length of 2 to 3 μs with a 10- to 20 kHz PRF. The receiver was a super-heterodyne type using Acorn tubes and a 6 MHz IF stage. The antenna consisted of 4 rows of 16 half-wave dipoles backed by a 3- by 3-meter mesh screen. The operator used a bicycle-type drive to rotate the antenna, and the elevation could be changed using a hand crank.
Several sets were completed, and one was put into operation on the Malievelt in The Hague
just before the Netherlands fell to Germany in May 1940. The set worked well, spotting enemy aircraft during the first days of fighting. To prevent capture, operating units and plans for the system were destroyed. Von Weiler and Max Staal fled to England aboard one of the last ships able to leave, carrying two disassembled sets with them. Later, Gratama and van Leeuwen also escaped to England.
(CSF) where he and Robert Warneck improved his father's magnetrons.
Emile Girardeau
,the head of the CSF, recalled in testimony that they were at the time intending to build radio-detection systems "conceived according to the principles stated by Tesla.The " In 1934,following systematic studies on the magnetron the research of the CSF, headed by Maurice Ponte submitted a patent application for a device for detecting obstacles using continuous radiation of ultra-short wavelengths produced by a magnetron.These were still CW systems and depended on Doppler
interference for detection .However antennas were collocated The device was measuring distance and azimuth but not directly as in the later "radar" on a screen (1939), but it was the first patent of an operational radio-detection apparatus using centimetric wavelengths.
The system was tested in late 1934 aboard the cargo ship Oregon, with two transmitters working at 80 cm and 16 cm wavelengths. Coastlines and boats were detected from a range of 10-12 nautical miles. The shortest wavelength was chosen for the final design, which equipped the liner SS Normandie
as early as mid-1935 for operational use.
In late 1937, Maurice Elie at SFR developed a means of pulse-modulating transmitter tubes. This led to a new 16-cm system with a peak power near 500 W and a pulse width of 6 μs. . French and U.S. patents were filed in December 1939. The system was planned to be sea-tested aboard the Normandie, but this was cancelled at the outbreak of war.
Pierre David at the Laboratori National de Radioelectricite (National Laboratory of Radioelectricity, LNR) experimented with reflected radio signals at about a meter wavelength. Starting in 1931, he observed that aircraft caused interference to the signals. The LNR then initiated research on a detection technique called barrage électromagnétique (electromagnetic curtain). While this could indicate the general location of penetration, precise determination of direction and speed was not possible.
In 1936, the Défense Aérienne de Territoire (Defence of Air Territory), ran tests on David’s electromagnetic curtain. In the tests, the system detected most of the entering aircraft, but too many were missed. As the war grew closer, the need for an aircraft detection was critical. David realized the advantages of a pulsed system, and in October 1938 he designed a 50 MHz, pulse-modulated system with a peak-pulse power of 12 kW. This was built by the firm SADIR.
France declared war on Germany on September 1, 1939, and there was a great need for an early-warning detection system. The SADIR system was taken to near Toulon
, and detected and measured the range of invading aircraft as far as 55 km (34.2 mi). The SFR pulsed system was set up near Paris where it detected aircraft at ranges up to 130 km (80.8 mi). To further improve the SFR system, Henri Gutton and Warnecke developed a 500-cm (600-MHz) magnetron with an oxide-coated cathode that produced 500 W. In May 1940, just before the Germans arrived, several of the new magnetrons were taken to Great Britain where their oxide-coated cathods were incorporated to improve the Boots and Randall magnetron.
initiated the research in Italy
on radio-based detection technology. In 1933, while participating with his Italian firm in experiments with a 600 MHz communications link across Rome
, he noted transmission disturbances caused by moving objects adjacent to its path. This led to the development at his laboratory at Cornegliano of a 330-MHz (0.91-m) CW Doppler detection system that he called radioecometro. Barkhausen-Kurz tube
s were used in both the transmitter and receiver.
In May 1935, Marconi demonstrated his system to the Fascist dictator Benito Mussolini
and members of the military General Staff; however the output power was insufficient for military use. While Marconi’s demonstration raised considerable interest, little more was done with his apparatus.
Mussolini directed that radio-based detection technology be further developed, and it was assigned to the Regio Instituto Electrotecnico e delle Comunicazioni (RIEC, Royal Institute for Electro-technics and Communications). The RIEC had been established in 1916 on the campus of the Italian Naval Academy
in Livorno
. Lieutenant Ugo Tiberio, a physics and radio-technology instructor at the Academy, was assigned to head the project on a part-time basis.
Tiberio prepared a report on developing an experimental apparatus that he called telemetro radiofonico del rivelatore (RDT, Radio-Detector Telemetry). The report, submitted in mid-1936, included what was later known as the radar range equation. When the work got underway, Nello Carrara, a civilian physics instructor who had been doing research at the RIEC in microwaves, was added to be responsible for developing the RDT transmitter.
Before the end of 1936, Tiberio and Carrara had demonstrated the EC-1, the first Italian RDT system. This had an FM
transmitter operating at 200 MHz (1.5 m) with a single parabolic
cylinder antenna. It detected by mixing the transmitted and the Doppler-shifted reflected signals, resulting in an audible tone.
The EC-1 did not provide a range measurement; to add this capability, development of a pulsed system was initiated in 1937. Captain Alfeo Brandimarte joined the group and primarily designed the first pulsed system, the EC-2. This operated at 175 MHz (1.7 m) and used a single antenna made with a number of equi-phased dipoles. The detected signal was intended to be displayed on an oscilloscope. There were many problems, and the system never reached the testing stage.
Work then turned to developing higher power and operating frequencies. Carrara, in cooperation with the firm FIVRE, developed a magnetron-like device. This was composed of a pair of triodes connected to a resonate cavity and produced 10 kW at 425 MHz (70 cm). It was used in designing two versions of the EC-3, one for shipboard and the other for coastal defense.
Italy, joining Germany, entered WWII in September 1939 without an operational RDT. A breadboard of the EC-3 was built and tested from atop a building at the Academy, but most RDT work was stopped as direct support of the war took priority.
, Canada
, New Zealand
, and South Africa
by September 1939. In addition, this technology was independently developed in Hungary
early in the war period.
In Australia, the Radiophysics Laboratory was established at Sydney University under the Council for Scientific and Industrial Research; John H. Piddington was responsible for RDF development. The first project was a 200-MHz (1.5-m) shore-defense system for the Australian Army
. Designated ShD, this was first tested in September 1941, and eventually installed at 17 ports. Following the Japanese attack on Pearl Harbor
, the Royal Australian Air Force
urgently needed an air-warning system, and Piddington’s team, using the ShD as a basis, put the AW Mark I together in five days. It was being installed in Darwin, Northern Territory
, when Australia received the first Japanese attack on February 19, 1942. A short time later, it was converted to a light-weight transportable version, the LW-AW Mark II; this was used by the Australian forces, as well as the U.S. Army, in early island landings in the South Pacific.
The early RDF developments in Canada were at the Radio Section of the National Research Council of Canada
. Using commercial components and with essentially no further assistance from Great Britain, John Tasker Henderson led a team in developing the Night Watchman, a surface-warning system for the Royal Canadian Navy
to protect the entrance to the Halifax Harbour
. Successfully tested in July 1940, this set operated at 200 MHz (1.5 m), had a 1 kW output with a pulse length of 0.5 μs, and used a relatively small, fixed antenna. This was followed by a ship-borne set designated Surface Warning 1st Canadian (SW1C) with the antenna hand-rotated; this was first tested at sea in mid-May 1941, For coastal defense by the Canadian Army
, a 200 MHz set with a transmitter similar to the Night Watchman was developed. Designated CD, it used a large, rotating antenna atop a 70 feet (21.3 m) wooden tower. The CD was put into operation in January 1942.
Ernest Marsden
represented New Zealand at the briefings in England, and then established two facilities for RDF development – one in Wellington
at the Radio Section of the Central NZ Post Office, and another at Canterbury University College in Christchurch
. Charles N. Watson-Munro led the development of land-based and airborne sets at Wellington, while Frederick W. G. White led the development of shipboard sets at Christchurch.
Before the end of 1939, the Wellington group had converted an existing 180-MHz (1.6-m), 1 kW transmitter to produce 2-μs pulses and tested it to detect large vessels at up to 30 km; this was designated CW (Coastal Watching). A similar set, designated CD (Coast Defense) used a CRT for display and had lobe-switching on the receiving antenna; this was deployed in Wellington in late 1940. A partially completed ASV 200 MHz set was brought from Great Britain by Marsden, and another group at Wellington built this into an aircraft set for the Royal New Zealand Air Force
; this was first flown in early 1940. At Christchurch, there was a smaller staff and work went slower, but by July 1940, a 430-MHz (70-cm), 5 kW set was tested. Two types, designated SW (Ship Warning) and SWG (Ship Warning, Gunnery), were placed into service by the Royal New Zealand Navy
starting in August 1941. In all some 44 types were developed in New Zealand during WW11.
South Africa did not have a representative at the 1939 meetings in England, but in mid-September, as Ernest Marsden was returning by ship to New Zealand, Basil F. J. Schonland
came aboard and received three days of briefings. Schonland, a world authority on lightning and Director of the Bernard Price Institute of Geophysics at Witwatersrand University, immediately started an RDF development using amateur radio components and Institute’s lightning-monitoring equipment. Designated JB (for Johannesburg
), the 90-MHz (3.3-m), 500-W mobile system was tested in November 1939, just two months after its start. The prototype was operated in Durban
before the end of 1939, detecting ships and aircraft at distances up to 80 km, and by the next March a system was fielded by anti-aircraft brigades of the South African Defence Force
.
In Hungary, Zoltán Lajos Bay
was a Professor of Physics at the Technical University of Budapest as well as the Research Director of Egyesült Izzolampa (IZZO), a radio and electrical manufacturing firm. In late 1942, IZZO was directed by the Minister of Defense to develop a radio-location (rádiólokáció, radar) system. Using journal papers on ionospheric measurements for information on pulsed transmission, Bay developed a system called Sas (Eagle) around existing communications hardware.
The Sas operated at 120 MHz (2.5 m) and was in a cabin with separate transmitting and receiving dipole arrays attached; the assembly was all on a rotatable platform. According to published records, the system was tested in 1944 atop Mount János and had a range of “better than 500 km.” A second Sas was installed at another location. There is no indication that either Sas installation was ever in regular service. After the war, Bay used a modified Sas to successfully bounce a signal off the moon.
in September 1939, both the United Kingdom
and Germany
knew of each other's ongoing efforts in radio navigation
and its countermeasures – the "Battle of the beams
". Also, both nations were generally aware of, and intensely interested in, the other's developments in radio-based detection and tracking, and engaged in an active campaign of espionage
and false leaks about their respective equipment. By the time of the Battle of Britain
, both sides were deploying range and direction-finding units (radars) and control stations as part of integrated air defense capability. However, the German Funkmessgerät (radio measuring device) systems could not assist in an offensive role and was thus not supported by Adolf Hitler
. Also, the Luftwaffe
did not sufficiently appreciate the importance of British Range and Direction Finding
(RDF) stations as part of RAF
's air defense capability, contributing to their failure.
While the United Kingdom and Germany led in pre-war advances in the use of radio for detection and tracking of aircraft, there were also developments in the United States, the Soviet Union, and Japan. Wartime systems in all of these nations will be summarized. The acronym RADAR (for RAdio Detection And Ranging) was coined by the U.S. Navy in 1940, and the subsequent name "radar" was soon widely used.
.
Even before the end of the war, various project directed toward non-military applications of radar and closely related technologies were initiated. The US Army Air Forces and the British RAF had made wartime advances in using radar for handling aircraft landing, and this was rapidly expanded into the civil sector. The field of radio astronomy
was one of the related technologies; although discovered before the war, it immediately flourished in the late 1940s with many scientists around the world establishing new careers based on their radar experience.
Four techniques, highly important in post-war radars, were matured in the late 1940s-early 1950s: pulse Doppler, monopulse, phased array, and synthetic aperture; the first three were known and even used during wartime developments, but were matured later.
One of the early applications of digital computers
was in switching the signal phase in elements of large phased-array antennas. As smaller computers came into being, these were quickly applied to digital signal processing
using algorithms for improve radar performance.
Other advances in radar systems and applications in the decades following WWII are far too many to be included herein. The following sections are intended to provide representative samples.
(USAF) – separated from the Army in 1946 – concentrated radar research at their Cambridge Research Center (CRC) at Hanscom Field
, Massachusetts. In 1951, MIT opened the Lincoln Laboratory
for joint developments with the CRC. While the Bell Telephone Laboratories embarked on major communications upgrades, they continued with the Army in radar for their ongoing Nike air-defense program
In Great Britain, the RAF’s Telecommunications Research Establishment
(TRE) and the Army’s Radar Research and Development Establishment
(RRDE) both continued at reduced levels at Malvern, Worcestershire
, then in 1953 were combined to form the Radar Research Establishment. In 1948, all of the Royal Navy’s radio and radar R&D activities were combined to form the Admiralty Signal and Radar Establishment
, located near Portsmouth
, Hampshire
. The USSR, although devastated by the war, immediately embarked on the development of new weapons, including radars.
During the Cold War
period following WWII, the primary "axis" of combat shifted to lie between the United States and the Soviet Union
. By 1949, both sides had nuclear weapons carried by bombers. To provide early warning of an attack, both deployed huge radar networks of increasing sophistication at ever-more remote locations. In the West, the first such system was the Pinetree Line
, deployed across Canada in the early 1950s, backed up with radar picket
s on ships and oil platforms off the east and west coasts.
The Pinetree Line initially used vintage pulsed radars and was soon supplemented with the Mid-Canada Line
(MCL). Soviet technology improvements made these Lines inadequate and, in a construction project involving 25,000 persons, the Distant Early Warning Line
(DEW Line) was completed in 1957. Stretching from Alaska
to Baffin Island
and covering over 6000 miles (9,656 km), the DEW Line consisted of 63 stations with AN/FPS-19 high-power, pulsed, L-Band radars, most augmented by AN/FPS-23 pulse-Doppler systems. The Soviet Unit tested its first Intercontinental Ballistic Missile
(ICBM) in August 1957, and in a few years the early-warning role was passed almost entirely to the more capable DEW Line.
Both the U.S. and the Soviet Union then had ICBMs with nuclear warheads, and each began the development of a major anti-ballistic missile (ABM) system. In the USSR, this was the Fakel V-1000, and for this they developed powerful radar systems. This was eventually deployed around Moscow as the A-35 anti-ballistic missile system
, supported by radars designated by NATO as the Cat House
, Dog House, and Hen House.
In 1957, the U.S. Army initiated an ABM system first called Nike-X; this passed through several names, eventually becoming the Safeguard Program
. For this, there was a long-range Perimeter Acquisition Radar (PAR) and a shorter-range, more precise Missile Site Radar (MSR).
The PAR was housed in a 128 feet (39 m)-high nuclear-hardened building with one face sloping 25 degrees facing north. This contained 6,888 antenna elements separated in transmitting and receiving phased arrays. The L-Band transmitter used 128 long-life traveling-wave tubes (TWTs), having a combined power in the megawatt range The PAR could detect incoming missiles outside the atmosphere at distances up to 1800 miles (2,896.8 km).
The MSR had an 80 feet (24.4 m), truncated pyramid structure, with each face holding a phased-array antenna 13 feet (4 m) in diameter and containing 5,001 array elements used for both transmitting and receiving. Operating in the S-Band, the transmitter used two klystron
s functioning in parallel, each with megawatt-level power. The MSR could search for targets from all directions, acquiring them at up to 300 miles (482.8 km) range.
One Safeguard site, intended to defend Minuteman ICBM
missile silos near the Grand Forks AFB in North Dakota
, was finally completed in October 1975, but the U.S. Congress withdrew all funding after it was operational but a single day. During the following decades, the U.S. Army and the U.S. Air Force developed a variety of large radar systems, but the long-serving BTL gave up military development work in the 1970s.
A modern radar developed by of the U.S. Navy that should be noted is the AN/SPY-1
. First fielded in 1973, this S-Band, 6 MW system has gone through a number of variants and is a major component of the Aegis Combat System
. An automatic detect-and-track system, it is computer controlled using four complementary three-dimensional passive electronically scanned array
antennas to provide hemispherical coverage.
Radar signals, traveling with line-of-sight propagation
, normally have a range to ground targets limited by the visible horizon
, or less than about 10 miles (16.1 km). Airborne targets can be detected by ground-level radars at greater ranges, but, at best, several hundred miles. Since the beginning of radio, it had been known that signals of appropriate frequencies (3 to 30 MHz) could be “bounced” from the ionosphere
and received at considerable distances. As long-range bombers and missiles came into being, there was a need to have radars give early warnings at great ranges. In the early 1950s, a team at the Naval Research Laboratory came up with the Over-the-Horizon (OTH) radar
for this purpose.
To distinguish targets from other reflections, it was necessary to use a phase-Doppler system. Very sensitive receivers with low-noise amplifier
s had to be developed. Since the signal going to the target and returning had a propagation loss proportional to the range raised to the fourth power, a powerful transmitter and large antennas were required. A digital computer with considerable capability (new at that time) was necessary for analyzing the data. In 1950, their first experimental system was able to detect rocket launches 600 miles (965.6 km) away at Cape Canaveral, and the cloud from a nuclear explosion in Nevada 1700 miles (2,735.9 km) distant.
In the early 1970s, a joint American-British project, code named Cobra Mist
, used a 10-MW OTH radar at Orfordness (the birthplace of British radar), England, in an attempt to detect aircraft and missile launchings over the Western USSR. Because of US-USSR ABM agreements, this was abandoned within two years. In the same time period, the Soviets were developing a similar system; this successfully detected a missile launch at 2500 km (1,553.4 mi). By 1976, this had matured into an operational system named Duga (“Arc” in English), but known to western intelligence as Steel Yard and called Woodpecker
by radio amateurs and others who suffered from its interference – the transmitter was estimated to have a power of 10 MW. Australia, Canada, and France also developed OTH radar systems.
With the advent of satellite
s with early-warning capabilities, the military lost most of its interest in OTH radars. However, in recent years, this technology has been reactivated for detecting and tracking ocean shipping in applications such as maritime reconnaissance and drug enforcement.
Systems using an alternate technology have also been developed for over-the-horizon detection. Due to diffraction
, electromagnetic surface wave
s are scattered to the rear of objects, and these signals can be detected in a direction opposite from high-powered transmissions. Called OTH-SW (SW for Surface Wave), Russia is using such a system to monitor the Sea of Japan
, and Canada has a system for coastal surveillance.
(ATC) – the introduction of radar. In 1946, the Civil Aeronautics Administration (CAA) unveiled an experimental radar-equipped tower for control of civil flights. By 1952, the CAA had begun its first routine use of radar for approach and departure control. Four years later, it placed a large order for long-range radars for use in en route ATC; these had the capability, at higher altitudes, to see aircraft within 200 nautical miles (370 km). In 1960, it became required for aircraft flying in certain areas to carry a radar transponder
that identified the aircraft and helped improve radar performance. Since 1966, the responsible agency has been called the Federal Aviation Administration
(FAA).
A Terminal Radar Approach Control
(TRACON) is an ATC facility usually located within the vicinity of a large airport. In the US Air Force it is known as RAPCON (Radar Approach Control), and in the US Navy as a RATCF (Radar Air Traffic Control Facility). Typically, the TRACON controls aircraft within a 30 to 50 nautical mile (56 to 93 km) radius of the airport at an altitude between 10,000 to 15,000 feet (3,000 to 4,600 m). This uses one or more Airport Surveillance Radar
s (ASR-7, 8, & 9), sweeping the sky once every few seconds.
The Digital Airport Surveillance Radar
(DASR) is a newer TRACOM radar system, replacing the old analog systems with digital technology. The civilian nomenclature for this radar is the ASR-11, and AN/GPN-30 is used by the military. Two radar systems are included. The primary is an X-Band (~2.8 GHz) system with 25 kW pulse power. It provides 3-D tracking of target aircraft and also measures rainfall intensity. The secondary is a P-Band (~1.05 GHz) system with a peak-power of about 25 kW. It uses a transponder set to interrogate aircraft and receive operational data. The antennas for both systems rotate atop a tall tower.
was established in 1870 with a specific mission:
In fulfilling this mission, the Weather Bureau established the first radio network in the United States – possibly in the world – shortly after the Galveston hurricane of 1900, one of the greatest natural disaster in America’s history. The continued use of technologies carried into the post-war era with the use of radar for meteorological monitoring. Today, the name “radar” is, to most people, tied to weather reports and warnings via the television.
The WSR-1
(Weather Surveillance Radar-1) was one of the first weather radars. This was a modified version of the AN/APS-2F
radar, which the Weather Bureau acquired from the Navy. The WSR-1A, WSR-3, and WSR-4 were also variants of this radar. The Weather Bureau later became the National Weather Service
(NWS), and is now an agency of the National Oceanic and Atmospheric Administration
(NOAA).
The WSR-57
(Weather Surveillance Radar – 1957) was the first weather radar designed specifically for a national warning network. Using WWII technology based on vacuum tubes, it gave only coarse reflectivity data and no velocity information. Operating at 2.89 GHz (S-Band), it had a peak-power of 410 kW and a maximum range of about 580 mi (933.4 km). AN/FPS-41 was the military designation for the WSR-57.
The next significant change was the WSR-74
series, beginning operations in 1974. There were two types: the WSR-74S, for replacements and filling gaps in the WSR-57 national network, and the WSR-74C, primarily for local use. Both were transistor-based, and their primary technical difference was indicated by the letter, S-Band (better suited for long range) and C-Band, respectively.
Until the 1990s, there were 128 of the WSR-57 and WSR-74 model radars were spread across the country in the NWS radar network. They were gradually replaced by the WSR-88D (Weather Surveillance Radar – 1988, Doppler), commonly known as NEXRAD
(Next Generation Radar). There are now over 150 NEXRAD sites networked in the United States and selected overseas locations.
The WSR-88D has a klystron
-based 2.7-3.0-GHz (S-Band) transmitter producing 750 kW peak-power into a parabolic-dish antenna. The PRF is selectable between 318 and 1304 Hz. The system provides reflectivity data at 0.25 km by 0.5 degree to 460 km (285.8 mi) range, and Doppler data at 0.25 km by 0.5 degree to 230 km (142.9 mi) range.
In 1998, the NWS began using the Advanced Weather Interactive Processing System
(AWIPS). This is a technologically advanced, interactive computer system that integrates data from the NEXRAD network with satellite imagery
and surface observations for preparing forecasts and issuing warnings. With upgrades, this provides the images now well known to weather television watchers.
, dating from the early days of radar and still the most common type of display, provides a map of the targets surrounding the radar location. If the radar antenna on an aircraft is aimed downward, a map of the terrain is generated, and the larger the antenna, the greater the image resolution. After centimeter radar came into being, downward-looking radars – the H2S
( L-Band) and H2X
(C-Band) – provided real-time maps used by the U.S. and Great Britain in bombing runs over Europe at night and through dense clouds.
In 1951, Carl Wiley led a team at Goodyear Aircraft Corporation (later Goodyear Aerospace
) in developing a technique for greatly expanding and improving the resolution of radar-generated images. Called synthetic aperture radar
(SAR), an ordinary-sized antenna fixed to the side of an aircraft is used with highly complex signal processing to give an image that would otherwise require a much larger, scanning antenna; thus, the name synthetic aperture. As each pulse is emitted, it is radiated over a lateral band onto the terrain. The return is spread in time, due to reflections from features at different distances. Motion of the vehicle along the flight path gives the horizontal increments. The amplitude and phase of returns are combined by the signal processor using Fourier transform
techniques in forming the image. The overall technique is closely akin to optical holography
.
Through the years, many variations of the SAR have been made with diversified applications resulting. In initial systems, the signal processing was too complex for on-board operation; the signals were recorded and processed later. Processors using optical techniques were then tried for generating real-time images, but advances in high-speed electronics now allow on-board processes for most applications. Early systems gave a resolution in tens of meters, but more recent airborne systems provide resolutions to about 10 cm. Current ultra-wideband
systems have resolutions of a few millimeters.
. This is a small, usually hand-held, Doppler radar
that is used to detect the speed of objects, especially trucks and automobiles in regulating traffic, as well as pitched baseballs, runners, or other moving objects in sports. This device can also be used to measure the surface speed of water and continuously manufactured materials. A radar gun does not return information regarding the object's position; it uses the Doppler effect
to measure the speed of a target. First developed in 1954, most radar guns operate with very low power in the X or Ku Bands. Some use infrared
radiation or laser
light; these are usually called LIDAR
. A related technology for velocity measurements in flowing liquids or gasses is called laser Doppler velocimetry
; this technology dates from the mid-1960s.
(PRF), a shorter pulse results in a higher peak power. Harmonic analysis
shows that the narrower the pulse, the wider the band of frequencies that contain the energy, leading to such systems also being called wide-band radars. In the early days, the electronics for generating and receiving these pulses was not available; thus, essentially no applications of this were initially made.
By the 1970s, advances in electronics led to renewed interest in what was often called short-pulse radar. With further advances, it became practical to generate pulses having a width on the same order as the period of the RF carrier (T = 1/f). This is now generally called impulse radar.
The first significant application of this technology was in ground-penetrating radar
(GPR). Developed in the 1970s, GPR is now used for structural foundation analysis, archeological mapping, treasure hunting, unexploded ordinance identification, and other shallow investigations. This is possible because impulse radar can concisely locate the boundaries between the general media (the soil) and the desired target. The results, however, are non-unique and are highly dependant upon the skill of the operator and the subsequent interpretation of the data.
In dry or otherwise favorable soil and rock, penetration up to 300 feet (91.4 m) is often possible. For distance measurements at these short ranges, the transmitted pulse is usually only one radio-frequency cycle in duration; With a 100 MHz carrier and a PRF of 10 kHz (typical parameters), the pulse duration is only 10 ns (nanosecond). leading to the "impulse" designation. A variety of GPR systems are commercially available in back-pack and wheeled-cart versions with pulse-power up to a kilowatt.
With continued development of electronics, systems with pulse durations measured in picosecond
s became possible. Applications are as varied as security and motion sensors, building stud-finders, collision-warning devices, and cardiac-dynamics monitors. Some of these devices are match-box sized, including a long-life power source.
had this as a major objective as he developed a radar in Hungary. Sadly, his radar telescope was taken away by the conquering Soviet army and had to be rebuilt, thus delaying the experiment. Under Project Diana
conducted by the Army’s Evans Signal Laboratory in New Jersey, a modified SCR-271 radar (the fixed-position version of the SCR-270
) operating at 110 MHz with 3 kW peak-power, was used in receiving echoes from the Moon on January 10, 1946. Zoltán Bay accomplished this on the following February 6.
Radio astronomy
also had its start following WWII, and many scientists involved in radar development then entered this field. A number of radio observatories were constructed during the following years; however, because of the additional cost and complexity of involving transmitters and associated receiving equipment, very few were dedicated to radar astronomy. In fact, essentially all major radar astronomy activities have been conducted as adjuncts to radio astronomy observatories.
The radio telescope
at the Arecibo Observatory
, opened in 1963, is the largest in the world. Owned by the U.S. National Science Foundation
and contractor operated, it is used primarily for radio astronomy, but equipment is available for radar astronomy. This includes transmitters operating at 47 MHz, 439 MHz, and 2.38 GHz, all with very-high pulse power. It has a 305-m (1,000-ft) primary reflector
fixed in position; the secondary reflector
is on tracks to allow precise pointing to different parts of the sky. Many significant scientific discoveries have been made using the Arecibo radar telescope, including mapping of surface roughness of Mars
and observations of Saturn
s and its largest moon, Titan
. In 1989, the observatory radar-imaged an asteroid
for the first time in history.
Several spacecraft orbiting the Moon, Mercury, Venus, Mars, and Saturn have carried radars for surface mapping; a ground-penetration radar was carried on the Mars Express
mission. Radar systems on a number of aircraft and orbiting spacecraft have mapped the entire Earth for various purposes; on the Shuttle Radar Topography Mission
, the entire planet was mapped at a 30-m resolution.
The Jodrell Bank Observatory, an operation of the University of Manchester
in Great Britain, was originally started by Bernard Lovell
to be a radar astronomy facility. It initially used a war-surplus GL-II radar system operating at 71 MHz (4.2 m). The first observations were of ionized trails in the Geminids
meteor shower during December 1945. While the facility soon evolved to become the third largest radio observatory in the world, some radar astronomy continued. The largest (250-ft or 76-m in diameter) of their three fully steerable radio telescopes became operational just in time to radar track Sputnik 1
, the first artificial satellite, in October 1957.
James Clerk Maxwell
James Clerk Maxwell of Glenlair was a Scottish physicist and mathematician. His most prominent achievement was formulating classical electromagnetic theory. This united all previously unrelated observations, experiments and equations of electricity, magnetism and optics into a consistent theory...
's seminal work on electromagnetism
Electromagnetism
Electromagnetism is one of the four fundamental interactions in nature. The other three are the strong interaction, the weak interaction and gravitation...
. However, it was not until the early 20th century that systems able to use these principles were becoming widely available, and it was German engineer Christian Huelsmeyer who first used them to build a simple ship detection device intended to help avoid collisions in fog (Reichspatent Nr. 165546). Numerous similar systems were developed over the next two decades.
The name radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...
comes from the acronym RADAR, coined in 1940 by the U.S. Navy for public reference to their highly classified work in Radio Detection And Ranging. Thus, a true radar system must both detect and provide range (distance) information for a target. Before 1934, no single system gave this performance; some systems were omni-directional and provided ranging information, while others provided rough directional information but not range. A key development was the use of pulses that were timed to provide ranging, which were sent from large antennas that provided accurate directional information. Combining the two allowed for accurate plotting of targets.
Worldwide differential in antecedence
In the 1934–1939 period, eight nations developed, independently and in great secrecy, systems of this type: the United StatesUnited States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, Great Britain
Great Britain
Great Britain or Britain is an island situated to the northwest of Continental Europe. It is the ninth largest island in the world, and the largest European island, as well as the largest of the British Isles...
, Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
, the USSR, Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, the Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
, France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
, and Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
. In addition, Great Britain had shared their basic information with four Commonwealth countries: Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, and South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
, and these countries had also developed indigenous radar systems. During the war, Hungary
Hungary
Hungary , officially the Republic of Hungary , is a landlocked country in Central Europe. It is situated in the Carpathian Basin and is bordered by Slovakia to the north, Ukraine and Romania to the east, Serbia and Croatia to the south, Slovenia to the southwest and Austria to the west. The...
was added to this list.
Progress during the war was rapid and of great importance, probably one of the decisive factors for the victory of the Allies
Allies of World War II
The Allies of World War II were the countries that opposed the Axis powers during the Second World War . Former Axis states contributing to the Allied victory are not considered Allied states...
. By the end of hostilities, the United States, Great Britain, Germany, the USSR, and Japan had a wide diversity of land- and sea-based radars as well as small airborne systems. After the war, radar use was widened to numerous fields including: civil aviation
Civil aviation
Civil aviation is one of two major categories of flying, representing all non-military aviation, both private and commercial. Most of the countries in the world are members of the International Civil Aviation Organization and work together to establish common standards and recommended practices...
, marine navigation, radar gun
Radar gun
A radar speed gun is a small doppler radar unit used to measure the speed of moving objects, including vehicles, pitched baseballs, runners and other moving objects. Radar speed guns may be hand-held, vehicle-mounted or static...
s for police, meteorology
Meteorology
Meteorology is the interdisciplinary scientific study of the atmosphere. Studies in the field stretch back millennia, though significant progress in meteorology did not occur until the 18th century. The 19th century saw breakthroughs occur after observing networks developed across several countries...
and even medicine.
Significance
The place of radar in the larger story of science and technology is argued differently by different authors. On the one hand, radar contributed very little to theory, which was largely known since the days of Maxwell and Hertz. Therefore radar did not advance science, but was simply a matter of technology and engineering. Maurice Ponte, one of the developers of radar in France, states:- Le principe fondamental du radar appartient au patrimoine commun des physiciens : ce qui demeure en fin de compte au crédit réel des techniciens se mesure à la réalisation effective de matériels opérationnels., or roughly
- The fundamental principle of the radar belongs to the common patrimony of the physicists : after all, what is left to the real credit of the technicians is measured by the effective realisation of operational materials.
But others point out the immense practical consequences of the development of radar. Far more than the atomic bomb, radar contributed to Allied victory in World War II. Robert Buderi states that it was also the precursor of much modern technology. From a review of his book:
. . . radar has been the root of a wide range of achievements since the war, producing a veritable family tree of modern technologies. Because of radar, astronomers can map the contours of far-off planets, physicians can see images of internal organs, meteorologists can measure rain falling in distant places, air travel is hundreds of times safer than travel by road, long-distance telephone calls are cheaper than postage, computers have become ubiquitous and ordinary people can cook their daily dinners in the time between sitcoms, with what used to be called a radar range.
Heinrich Hertz
In 1887 the German physicistPhysicist
A physicist is a scientist who studies or practices physics. Physicists study a wide range of physical phenomena in many branches of physics spanning all length scales: from sub-atomic particles of which all ordinary matter is made to the behavior of the material Universe as a whole...
Heinrich Hertz (1857–1894) began experimenting with electromagnetic waves in his laboratory. He found that these waves could be transmitted through different types of materials, and were reflected by others, such as conductor
Electrical conductor
In physics and electrical engineering, a conductor is a material which contains movable electric charges. In metallic conductors such as copper or aluminum, the movable charged particles are electrons...
s and dielectric
Dielectric
A dielectric is an electrical insulator that can be polarized by an applied electric field. When a dielectric is placed in an electric field, electric charges do not flow through the material, as in a conductor, but only slightly shift from their average equilibrium positions causing dielectric...
s. The existence of electromagnetic waves was predicted earlier by the Scottish physicist James Clerk Maxwell
James Clerk Maxwell
James Clerk Maxwell of Glenlair was a Scottish physicist and mathematician. His most prominent achievement was formulating classical electromagnetic theory. This united all previously unrelated observations, experiments and equations of electricity, magnetism and optics into a consistent theory...
(1831–79), but it was Hertz who first succeeded in generating and detecting what were soon called radio waves
Radio waves
Radio waves are a type of electromagnetic radiation with wavelengths in the electromagnetic spectrum longer than infrared light. Radio waves have frequencies from 300 GHz to as low as 3 kHz, and corresponding wavelengths from 1 millimeter to 100 kilometers. Like all other electromagnetic waves,...
.
Guglielmo Marconi
The development of the wireless or radio is often attributed to Guglielmo MarconiGuglielmo Marconi
Guglielmo Marconi was an Italian inventor, known as the father of long distance radio transmission and for his development of Marconi's law and a radio telegraph system. Marconi is often credited as the inventor of radio, and indeed he shared the 1909 Nobel Prize in Physics with Karl Ferdinand...
(1874–1937). Although he was not the first to "invent" this technology, it might be said that he was the greatest early promoter of practical radio systems and their applications. In a paper read before the Institution of Electrical Engineers in London on March 3, 1899, Marconi described radio beacon experiments he had conducted in Salisbury Plain. Concerning this lecture, in a 1922 paper he wrote:
- I also described tests carried out in transmitting a beam of reflected waves across country . . . and pointed out the possibility of the utility of such a system if applied to lighthouses and lightships, so as to enable vessels in foggy weather to locate dangerous points around the coasts...
- It [now] seems to me that it should be possible to design [an] apparatus by means of which a ship could radiate or project a divergent beam of these rays in any desired direction, which rays, if coming across a metallic object, such as another steamer or ship, would be reflected back to a receiver screened from the local transmitter on the sending ship, and thereby immediately reveal the presence and bearing of the other ship in fog or thick weather.
This paper and a speech presenting the paper to a joint meeting of the Institute of Radio Engineers and the American Institute of Electrical Engineers in New York City on June 20, 1922, is often cited as the seminal event which began widespread interest in the development of radar.
Christian Huelsmeyer
In 1904 Christian Huelsmeyer (1881–1957) gave public demonstrations in GermanyGermany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
and the Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
of the use of radio echoes
Echo (phenomenon)
In audio signal processing and acoustics, an echo is a reflection of sound, arriving at the listener some time after the direct sound. Typical examples are the echo produced by the bottom of a well, by a building, or by the walls of an enclosed room and an empty room. A true echo is a single...
to detect ship
Ship
Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...
s so that collisions could be avoided. His device consisted of a simple spark gap
Spark gap
A spark gap consists of an arrangement of two conducting electrodes separated by a gap usually filled with a gas such as air, designed to allow an electric spark to pass between the conductors. When the voltage difference between the conductors exceeds the gap's breakdown voltage, a spark forms,...
used to generate a signal that was aimed using a dipole antenna
Dipole antenna
A dipole antenna is a radio antenna that can be made of a simple wire, with a center-fed driven element. It consists of two metal conductors of rod or wire, oriented parallel and collinear with each other , with a small space between them. The radio frequency voltage is applied to the antenna at...
with a cylindrical parabolic reflector
Parabolic reflector
A parabolic reflector is a reflective device used to collect or project energy such as light, sound, or radio waves. Its shape is that of a circular paraboloid, that is, the surface generated by a parabola revolving around its axis...
. When a signal reflected from a ship was picked up by a similar antenna attached to the separate coherer
Coherer
The coherer was a primitive form of radio signal detector used in the first radio receivers during the wireless telegraphy era at the beginning of the twentieth century. Invented around 1890 by French scientist Édouard Branly, it consisted of a tube or capsule containing two electrodes spaced a...
receiver
Receiver (radio)
A radio receiver converts signals from a radio antenna to a usable form. It uses electronic filters to separate a wanted radio frequency signal from all other signals, the electronic amplifier increases the level suitable for further processing, and finally recovers the desired information through...
, a bell sounded. During bad weather or fog, the device would be periodically "spun" to check for nearby ships. The apparatus detected presence of ships up to 3 km, and Huelsmeyer planned to extend its capability to 10 km. It did not provide range (distance) information, only warning of a nearby object. He patented the device, called the telemobiloscope, but due to lack of interest by the naval authorities the invention was not put into production.
Huelsmeyer also received a patent amendment for estimating the range to the ship. Using a vertical scan of the horizon with the telemobiloscope mounted on a tower, the operator would find the angle at which the return was the most intense and deduce, by simple triangulation, the approximate distance. This is in contrast to the later development of pulsed radar, which determines distance directly.
Nikola Tesla
One of the hundreds of concepts generated by Nikola TeslaNikola Tesla
Nikola Tesla was a Serbian-American inventor, mechanical engineer, and electrical engineer...
(1856–1943) included principles regarding frequency and power levels for primitive radio-location units. In an interview published in The Electrical Experimenter, August 1917, Tesla gave the following:
- For instance, by their [standing electromagnetic waves] use we may produce at will, from a sending station, an electrical effect in any particular region of the globe; [with which] we may determine the relative position or course of a moving object, such as a vessel at sea, the distance traversed by the same, or its speed.
Tesla also proposed the use of these standing electromagnetic waves
Standing wave
In physics, a standing wave – also known as a stationary wave – is a wave that remains in a constant position.This phenomenon can occur because the medium is moving in the opposite direction to the wave, or it can arise in a stationary medium as a result of interference between two waves traveling...
along with pulsed reflected surface wave
Surface wave
In physics, a surface wave is a mechanical wave that propagates along the interface between differing media, usually two fluids with different densities. A surface wave can also be an electromagnetic wave guided by a refractive index gradient...
s to determine the relative position, speed, and course of a moving object and other modern concepts of radar. Tesla had first proposed that radio location techniques might help find submarine
Submarine
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...
s (for which it is not well-suited) with a fluorescent screen indicator.
United States
In the United States, both the Navy and Army needed means of remotely locating enemy ships and aircraft. In 1930, both services initiated the development of radio equipment that could meet this need. There was little coordination of these efforts; thus, they will be described separately.United States Navy
In the autumn of 1922, Albert H. TaylorAlbert H. Taylor
Albert Hoyt Taylor was an American electrical engineer who made important early contributions to the development of radar.-Biography:...
and Leo C. Young
Leo C. Young
Leo C. Young was an American radio engineer who had many accomplishments during a long career at the U.S. Naval Research Laboratory...
at the U.S. Naval Aircraft Radio Laboratory were conducting communication experiments when they noticed that a wooden ship in the Potomac River
Potomac River
The Potomac River flows into the Chesapeake Bay, located along the mid-Atlantic coast of the United States. The river is approximately long, with a drainage area of about 14,700 square miles...
was interfering with their signals; in effect, they had demonstrated the first multistatic radar
Multistatic radar
A multistatic radar system contains multiple spatially diverse monostatic radar or bistatic radar components with a shared area of coverage. An important distinction systems based on these individual radar geometries is the added requirement for some level of data fusion to take place between...
, a system that uses separated transmitting and receiving antennas and detects targets due to changes in the signal. In 1930, Lawrence A. Hyland
Lawrence A. Hyland
Lawrence A. "Pat" Hyland was an American electrical engineer. He is one of several people credited with major contributions to the invention of radar, but is probably best known as the man who transformed Hughes Aircraft from Howard Hughes' aviation "hobby shop" into one of the world's leading...
working with Taylor and Young, now at the U.S. Naval Research Laboratory (NRL) in Washington, D.C., used a similar arrangement of radio equipment to detect a passing aircraft. This led to a proposal by Taylor for using this technique for detecting ships and aircraft.
A simple wave-interference apparatus can detect the presence of an object, but it cannot determine its location
Location (geography)
The terms location and place in geography are used to identify a point or an area on the Earth's surface or elsewhere. The term 'location' generally implies a higher degree of can certainty than "place" which often has an ambiguous boundary relying more on human/social attributes of place identity...
or velocity
Velocity
In physics, velocity is speed in a given direction. Speed describes only how fast an object is moving, whereas velocity gives both the speed and direction of the object's motion. To have a constant velocity, an object must have a constant speed and motion in a constant direction. Constant ...
. That had to await the invention of pulsed radar, and later, additional encoding techniques to extract this information from a CW signal. When Taylor's group at the NRL were unsuccessful in getting interference radio accepted as a detection means, Young suggested trying pulsing techniques. This would also allow the direct determination of range to the target. The British and the American research groups were independently aware of the advantages of such an approach, but the problem was to develop the timing equipment to make it feasible.
Robert Morris Page
Robert Morris Page
Robert Morris Page was an American physicist who was a leading figure in the development of radar technology. Later, Page served as the Director of Research for the U.S. Naval Research Laboratory.-Life and career:...
was assigned by Taylor to implement Young's suggestion. Page designed a transmitter operating at 60 MHz and pulsed 10 μs
Microsecond
A microsecond is an SI unit of time equal to one millionth of a second. Its symbol is µs.A microsecond is equal to 1000 nanoseconds or 1/1000 millisecond...
in duration and 90 μs between pulses. In December 1934, the apparatus was used to detect a plane at a distance of one mile (1.6 km) flying up and down the Potomac. Although the detection range was small and the indications on the oscilloscope monitor were almost indistinct, it demonstrated the basic concept of a pulsed radar system. Based on this, Page, Taylor, and Young are usually credited with building and demonstrating the world’s first true radar.
An important subsequent development by Page was the duplexer, a device that allowed the transmitter and receiver to use the same antenna without over-whelming or destroying the sensitive receiver circuitry. This also solved the problem associated with synchronization of separate transmitter and receiver antennas which is critical to accurate position determination of long-range targets.
The experiments with pulsed radar were continued, primarily in improving the receiver for handling the short pulses. In June 1936, the NRL's first prototype radar system, now operating at 28.6 MHz, was demonstrated to government officials, successfully tracking an aircraft at distances up to 25 miles (40.2 km). Their radar was based on low frequency
Low frequency
Low frequency or low freq or LF refers to radio frequencies in the range of 30 kHz–300 kHz. In Europe, and parts of Northern Africa and of Asia, part of the LF spectrum is used for AM broadcasting as the longwave band. In the western hemisphere, its main use is for aircraft beacon,...
signals, at least by today's standards, and thus required large antennas
Antenna (radio)
An antenna is an electrical device which converts electric currents into radio waves, and vice versa. It is usually used with a radio transmitter or radio receiver...
, making it impractical for ship or aircraft mounting.
Antenna size is inversely proportional to the operating frequency; therefore, the operating frequency of the system was increased to 200 MHz, allowing much smaller antennas. The frequency of 200 MHz was the highest possible with existing transmitter tubes and other components. The new system was successfully tested at the NRL in April 1937, That same month, the first sea-borne testing was conducted. The equipment was temporarily installed on the USS Leary
USS Leary (DD-158)
USS Leary was a Wickes-class destroyer in the United States Navy during World War II. She was named for Lieutenant Clarence F. Leary USNRF , posthumously awarded the Navy Cross in World War I....
, with a Yagi antenna
Yagi antenna
A Yagi-Uda array, commonly known simply as a Yagi antenna, is a directional antenna consisting of a driven element and additional parasitic elements...
mounted on a gun barrel for sweeping the field of view.
Based on success of the sea trials, the NRL further improved the system. Page developed the ring oscillator
Ring oscillator
A ring oscillator is a device composed of an odd number of NOT gates whose output oscillates between two voltage levels, representing true and false...
, allowing multiple output tubes and increasing the pulse-power to 15 kW in 5-µs pulses. A 20-by-23 feet (7 m), stacked-dipole “bedspring” antenna was used. In laboratory test during 1938, the system, now designated XAF
XAF RADAR
The XAF Radar was an experiment radar constructed in 1938, survived World War II as a historical artifact, and is now placed on exhibit at the Historical Electronics Museum, located in Linthicum, Maryland-Creation and development:...
, detected planes at ranges up to 100 miles (160.9 km). It was installed on the battleship USS New York for sea trials starting in January 1939, and became the first operational radio detection and ranging set in the U.S. fleet.
In May 1939, a contract was awarded to RCA
RCA
RCA Corporation, founded as the Radio Corporation of America, was an American electronics company in existence from 1919 to 1986. The RCA trademark is currently owned by the French conglomerate Technicolor SA through RCA Trademark Management S.A., a company owned by Technicolor...
for production. Designated CXAM
CXAM radar
The CXAM radar system was the first production radar system deployed on United States Navy ships. It followed several earlier prototype systems, such as the NRL radar installed in April 1937 on the destroyer ; its successor, the XAF, installed in December 1938 on the battleship ; and the first...
, deliveries started in May 1940. The acronym RADAR was coined from "Radio Detection And Ranging" as a cover reference to this highly secret technology. One of the first CXAM systems was placed aboard the USS California, a battleship that was sunk in the Japanese attack on Pearl Harbor on December 7, 1941.
United States Army
As the Great DepressionGreat Depression
The Great Depression was a severe worldwide economic depression in the decade preceding World War II. The timing of the Great Depression varied across nations, but in most countries it started in about 1929 and lasted until the late 1930s or early 1940s...
started, economic conditions led the U.S. Army Signal Corps to consolidate its widespread laboratory operations to Fort Monmouth, New Jersey. On June 30, 1930, these were designated the Signal Corps Laboratories
Signal Corps Laboratories
Signal Corps Laboratories was formed on June 30, 1930, as part of the U.S. Army Signal Corps at Fort Monmouth, New Jersey. Through the years, the SCL had a number of changes in name, but remained the operation providing research and development services for the Signal Corps.-Background:At the...
(SCL) and Lt. Colonel (Dr.) William R. Blair
William R. Blair
William Richards Blair was an American scientist and Army Officer who led the U.S. Signal Corps Laboratories during its formative years. He is often called the "Father of Army Radar."-Career and achievements:...
was appointed the SCL Director.
Among other activities, the SCL was made responsible for research in the detection of aircraft by acoustical and infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
radiation means. Blair had performed his doctoral research in the interaction of electromagnet waves with solid materials, and naturally gave attention to this type of detection. Initially, attempts were made to detect infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
radiation, either from the heat of aircraft engines or as reflected from large searchlights with infrared filters, as well as from radio signals generated by the engine ignition.
Some success was made in the infrared detection, but little was accomplished using radio. In 1932, progress at the Naval Research Laboratory (NRL) on radio interference for aircraft detection was passed on to the Army. While it does not appear that any of this information was used by Blair, the SCL did undertake a systematic survey of what was then known throughout the world about the methods of generating, modulating, and detecting radio signals in the microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
region.
The SCL's first definitive efforts in radio-based target detection started in 1934 when the Chief of the Army Signal Corps, after seeing a microwave demonstration by RCA
RCA
RCA Corporation, founded as the Radio Corporation of America, was an American electronics company in existence from 1919 to 1986. The RCA trademark is currently owned by the French conglomerate Technicolor SA through RCA Trademark Management S.A., a company owned by Technicolor...
, suggested that radio-echo techniques be investigated. The SCL called this technique radio position-finding (RPF). Based on the previous investigations, the SCL first tried microwaves. During 1934 and 1935, tests of microwave RPF equipment resulted in Doppler-shifted signals being obtained, initially at only a few hundred feet distance and later greater than a mile. These tests involved a bi-static arrangement, with the transmitter at one end of the signal path and the receiver at the other, and the reflecting target passing through or near the path.
Blair was evidently not aware of the success of a pulsed system at the NRL in December 1934. In an internal 1935 note, Blair had commented:
- Consideration is now being given to the scheme of projecting an interrupted sequence of trains of oscillations against the target and attempting to detect the echoes during the interstices between the projections.
In 1936, W. Delmar Hershberger, SCL’s Chief Engineer at that time, started a modest project in pulsed microwave transmission. Lacking success with microwaves, Hershberger visited the NRL (where he had earlier worked) and saw a demonstration of their pulsed set. Back at the SCL, he and Robert H. Noyes built an experimental apparatus using a 75 watt, 110 MHz (2.73 m) transmitter with pulse modulation and a receiver patterned on the one at the NRL. A request for project funding was turned down by the War Department
United States Department of War
The United States Department of War, also called the War Department , was the United States Cabinet department originally responsible for the operation and maintenance of the United States Army...
, but $75,000 for support was diverted from a previous appropriation for a communication project.
In October 1936, Paul E. Watson
Paul E. Watson
Paul E. Watson was a pioneer researcher in the development of radar. Born in Bangor, Maine, Watson was a civilian engineer employed by the U.S. Army Signal Corps from the late 1920s. In 1936, he was named Chief Engineer of a Signal Corps research group at Camp Evans in Fort Monmouth, New Jersey...
became the SCL Chief Engineer and led the project. A field setup near the coast was made with the transmitter and receiver separated by a mile. On December 14, 1936, the experimental set detected at up to 7 mi (11.3 km) range aircraft flying in and out of New York City
New York City
New York is the most populous city in the United States and the center of the New York Metropolitan Area, one of the most populous metropolitan areas in the world. New York exerts a significant impact upon global commerce, finance, media, art, fashion, research, technology, education, and...
.
Work then began on a prototype system. Ralph I. Cole headed receiver work and William S. Marks lead transmitter improvements. Separate receivers and antennas were used for azimuth and elevation
Elevation
The elevation of a geographic location is its height above a fixed reference point, most commonly a reference geoid, a mathematical model of the Earth's sea level as an equipotential gravitational surface ....
detection. Both receiving and the transmitting antennas used large arrays of dipole
Dipole
In physics, there are several kinds of dipoles:*An electric dipole is a separation of positive and negative charges. The simplest example of this is a pair of electric charges of equal magnitude but opposite sign, separated by some distance. A permanent electric dipole is called an electret.*A...
wires on wooden frames. The system output was intended to aim a searchlight
Searchlight
A searchlight is an apparatus that combines a bright light source with some form of curved reflector or other optics to project a powerful beam of light of approximately parallel rays in a particular direction, usually constructed so that it can be swiveled about.-Military use:The Royal Navy used...
. The first demonstration of the full set was made on the night of May 26, 1937. A bomber was detected and then illuminated by the searchlight. The observers included the Secretary of War, Henry A. Woodring; he was so impressed that the next day orders were given for the full development of the system. Congress gave an appropriation of $250,000.
The frequency was increased to 200 MHz (1.5 m). The transmitter used 16 tubes in a ring oscillator
Ring oscillator
A ring oscillator is a device composed of an odd number of NOT gates whose output oscillates between two voltage levels, representing true and false...
circuit (developed at the NRL), producing about 75 kW peak power. Major James C. Moore was assigned to head the complex electrical and mechanical design of lobe switching
Lobe switching
Lobe switching is a method used on early radar sets to improve tracking accuracy. It used two slightly separated antenna elements to send the beam slightly to either side of the midline of the antenna, switching between the two to find which one gave the stronger return, thereby indicating which...
antennas. Engineers from Western Electric
Western Electric
Western Electric Company was an American electrical engineering company, the manufacturing arm of AT&T from 1881 to 1995. It was the scene of a number of technological innovations and also some seminal developments in industrial management...
and Westinghouse
Westinghouse Electric (1886)
Westinghouse Electric was an American manufacturing company. It was founded in 1886 as Westinghouse Electric Company and later renamed Westinghouse Electric Corporation by George Westinghouse. The company purchased CBS in 1995 and became CBS Corporation in 1997...
were brought in to assist in the overall development. Designated SCR-268, a prototype was successfully demonstrated in late 1938 at Fort Monroe
Fort Monroe
Fort Monroe was a military installation in Hampton, Virginia—at Old Point Comfort, the southern tip of the Virginia Peninsula...
, Virginia. Production of SCR-268 sets was started by Western Electric in 1939, and it entered service in early 1941.
Even before the SCR-268 entered service, it had been greatly improved. In a project led by Major (Dr.) Harold A. Zahl
Harold A. Zahl
Harold A. Zahl was an American physicist who had a 35-year career with the U.S. Army Signal Corps Laboratories, making major contributions to radar development.-Career and accomplishments:...
, two new configurations evolved – the SCR-270 (mobile) and the SCR-271 (fixed-site). Operation at 106 MHz (2.83 m) was selected, and a single water-cooled tube provided 8 kW (100 kW pulsed) output power. Westinghouse received a production contract, and started deliveries near the end of 1940.
The Army deployed five of the first SCR-270 sets around the island of Oahu
Oahu
Oahu or Oahu , known as "The Gathering Place", is the third largest of the Hawaiian Islands and most populous of the islands in the U.S. state of Hawaii. The state capital Honolulu is located on the southeast coast...
in Hawaii
Hawaii
Hawaii is the newest of the 50 U.S. states , and is the only U.S. state made up entirely of islands. It is the northernmost island group in Polynesia, occupying most of an archipelago in the central Pacific Ocean, southwest of the continental United States, southeast of Japan, and northeast of...
. At 7:02 on the morning of December 7, 1941, one of these radars detected a flight of aircraft at a range of 136 miles (218.9 km) due north. The observation was passed on to an aircraft warning center where it was misidentified as a flight of U.S. bombers known to be approaching from the mainland. The alarm went unheeded, and at 7:48, the Japanese aircraft first struck at Pearl Harbor.
Great Britain
Robert Watson-Watt
Sir Robert Alexander Watson-Watt, KCB, FRS, FRAeS is considered by many to be the "inventor of radar". Development of radar, initially nameless, was first started elsewhere but greatly expanded on 1 September 1936 when Watson-Watt became...
joined the Meteorological Office
Met Office
The Met Office , is the United Kingdom's national weather service, and a trading fund of the Department for Business, Innovation and Skills...
as a meteorologist, working at an outstation at Aldershot
Aldershot
Aldershot is a town in the English county of Hampshire, located on heathland about southwest of London. The town is administered by Rushmoor Borough Council...
in Hampshire
Hampshire
Hampshire is a county on the southern coast of England in the United Kingdom. The county town of Hampshire is Winchester, a historic cathedral city that was once the capital of England. Hampshire is notable for housing the original birthplaces of the Royal Navy, British Army, and Royal Air Force...
. Over the next 20 years, he studied atmospheric phenomena and developed the use of radio signals generated by lightning
Lightning
Lightning is an atmospheric electrostatic discharge accompanied by thunder, which typically occurs during thunderstorms, and sometimes during volcanic eruptions or dust storms...
strikes to map out the position of thunderstorm
Thunderstorm
A thunderstorm, also known as an electrical storm, a lightning storm, thundershower or simply a storm is a form of weather characterized by the presence of lightning and its acoustic effect on the Earth's atmosphere known as thunder. The meteorologically assigned cloud type associated with the...
s. The difficulty in pinpointing the direction of these fleeting signals led to the use of rotatable directional antennas, and in 1923 the use of oscilloscope
Oscilloscope
An oscilloscope is a type of electronic test instrument that allows observation of constantly varying signal voltages, usually as a two-dimensional graph of one or more electrical potential differences using the vertical or 'Y' axis, plotted as a function of time,...
s in order to display the signals. An operator would periodically rotate the antenna and look for "spikes" on the oscilloscope to find the direction of a storm. The operation eventually moved to the outskirts of Slough
Slough
Slough is a borough and unitary authority within the ceremonial county of Royal Berkshire, England. The town straddles the A4 Bath Road and the Great Western Main Line, west of central London...
in Berkshire
Berkshire
Berkshire is a historic county in the South of England. It is also often referred to as the Royal County of Berkshire because of the presence of the royal residence of Windsor Castle in the county; this usage, which dates to the 19th century at least, was recognised by the Queen in 1957, and...
, and in 1927 formed the Radio Research Station (RRS), Slough, an entity under the Department of Scientific and Industrial Research
Department of Scientific and Industrial Research
Several countries have organizations called the Department of Scientific and Industrial Research, abbreviated DSIR.-United Kingdom:...
(DSIR). Watson Watt was appointed the RSS Superintendent.
As war clouds gathered over Great Britain, the likelihood of air raids and the threat of invasion by air and sea drove a major effort in applying science and technology to defence. In November 1934, the Air Ministry
Air Ministry
The Air Ministry was a department of the British Government with the responsibility of managing the affairs of the Royal Air Force, that existed from 1918 to 1964...
established the Committee for Scientific Survey of Air Defence (CSSAD) with the official function of considering "how far recent advances in scientific and technical knowledge can be used to strengthen the present methods of defence against hostile aircraft." Commonly called the “Tizard Committee” after its Chairman, Sir Henry Tizard
Henry Tizard
Sir Henry Thomas Tizard FRS was an English chemist and inventor and past Rector of Imperial College....
, this group had a profound influence on technical developments in Great Britain.
H. E. Wimperis, Director of Scientific Research at the Air Ministry and a member of the Tizard Committee, had read about Nikola Tesla
Nikola Tesla
Nikola Tesla was a Serbian-American inventor, mechanical engineer, and electrical engineer...
's claim of inventing a 'death ray
Death ray
The death ray or death beam was a theoretical particle beam or electromagnetic weapon of the 1920s through the 1930s that was claimed to have been invented independently by Nikola Tesla, Edwin R. Scott, Harry Grindell Matthews, and Graichen, as well as others...
.' Watson Watt, Superintendent of the RSS, Slough, was now well established as an authority in the field of radio, and in January 1935, Wimperis contacted him asking if radio might be used for such a device. After discussing this with his scientific assistant, Arnold F. 'Skip' Wilkins
Arnold Frederic Wilkins
Arnold Frederic Wilkins O.B.E., was a pioneer in developing the use of radar.-Early life:...
, Watson Watt wrote back that this was unlikely, but added the following comment: Attention is being turned to the still difficult, but less unpromising, problem of radio detection and numerical considerations on the method of detection by reflected radio waves will be submitted when required.
Over the following several weeks, Wilkins considered the radio detection problem. He outlined an approach and backed it with detailed calculations of necessary transmitter power, reflection characteristics of an aircraft, and needed receiver sensitivity. Watson Watt sent this information to the Air Ministry on February 12, 1935, in a secret report titled "The Detection of Aircraft by Radio Methods."
Northamptonshire
Northamptonshire is a landlocked county in the English East Midlands, with a population of 629,676 as at the 2001 census. It has boundaries with the ceremonial counties of Warwickshire to the west, Leicestershire and Rutland to the north, Cambridgeshire to the east, Bedfordshire to the south-east,...
. On February 26, 1935, a Handley Page Heyford
Handley Page Heyford
The Handley Page Heyford was a twin-engine British biplane bomber of the 1930s. Although it had a short service life, it equipped several squadrons of the RAF as one of the most important British bombers of the mid-1930s, and was the last biplane heavy bomber to serve with the RAF.-Design and...
bomber flew along a path between the receiving station and the transmitting towers of a BBC
BBC
The British Broadcasting Corporation is a British public service broadcaster. Its headquarters is at Broadcasting House in the City of Westminster, London. It is the largest broadcaster in the world, with about 23,000 staff...
shortwave
Shortwave
Shortwave radio refers to the upper MF and all of the HF portion of the radio spectrum, between 1,800–30,000 kHz. Shortwave radio received its name because the wavelengths in this band are shorter than 200 m which marked the original upper limit of the medium frequency band first used...
station in nearby Daventry
Daventry
Daventry is a market town in Northamptonshire, England, with a population of 22,367 .-Geography:The town is also the administrative centre of the larger Daventry district, which has a population of 71,838. The town is 77 miles north-northwest of London, 13.9 miles west of Northampton and 10.2...
. The aircraft reflected the 6 MHz (49 m) BBC signal, and this was readily detected by Doppler
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
-beat interference at ranges up to 8 mi (12.9 km). This convincing test, known as the Daventry Experiment, was witnessed by a representative from the Air Ministry, and led to the immediate authorization to build a full demonstration system.
Based on pulsed transmission as used for probing the ionosphere
Ionosphere
The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...
. a preliminary system was designed and built at the RRS by the team. Their existing transmitter had a peak power of about 1 kW, and Wilkins had estimated that 100 kW would be needed. Edward George Bowen
Edward George Bowen
Edward George 'Taffy' Bowen, CBE, FRS was a British physicist who made a major contribution to the development of radar, and so helped win both the Battle of Britain and the Battle of the Atlantic...
was added to the team to design and build such a transmitter. Bowens’ transmitter operated at 6 MHz (50 m), had a pulse-repetition rate of 25 Hz, a pulse width of 25 μs
Microsecond
A microsecond is an SI unit of time equal to one millionth of a second. Its symbol is µs.A microsecond is equal to 1000 nanoseconds or 1/1000 millisecond...
, and approached the desired power.
Orfordness, a narrow, 19 miles (30.6 km) peninsula
Peninsula
A peninsula is a piece of land that is bordered by water on three sides but connected to mainland. In many Germanic and Celtic languages and also in Baltic, Slavic and Hungarian, peninsulas are called "half-islands"....
in Suffolk
Suffolk
Suffolk is a non-metropolitan county of historic origin in East Anglia, England. It has borders with Norfolk to the north, Cambridgeshire to the west and Essex to the south. The North Sea lies to the east...
along the coast of the North Sea
North Sea
In the southwest, beyond the Straits of Dover, the North Sea becomes the English Channel connecting to the Atlantic Ocean. In the east, it connects to the Baltic Sea via the Skagerrak and Kattegat, narrow straits that separate Denmark from Norway and Sweden respectively...
, was selected as the test site. Here the equipment would be openly operated in the guise of an ionospheric monitoring station. In mid-May, 1935, the equipment was moved to Orfordness. Six wooden towers were erected, two for stringing the transmitting antenna, and four for corners of crossed receiving antennas. In June, general testing of the equipment began.
On June 17, the first target was detected—a Supermarine Scapa
Supermarine Scapa
-See also:...
flying boat at 17 mi (27.4 km) range. It is historically correct that on June 17, 1935, radio-based detection and ranging was first demonstrated in Great Britain. Watson Watt, Wilkins, and Bowen are generally credited with initiating what would later be called radar in this nation.
In December 1935, the British Treasury appropriated £60,000 for a five-station system called Chain Home
Chain Home
Chain Home was the codename for the ring of coastal Early Warning radar stations built by the British before and during the Second World War. The system otherwise known as AMES Type 1 consisted of radar fixed on top of a radio tower mast, called a 'station' to provide long-range detection of...
(CH), covering approaches to the Thames Estuary
Thames Estuary
The Thames Mouth is the estuary in which the River Thames meets the waters of the North Sea.It is not easy to define the limits of the estuary, although physically the head of Sea Reach, near Canvey Island on the Essex shore is probably the western boundary...
. The secretary of the Tizard Committee, Albert Percival Rowe, coined the acronym RDF as a cover for the work, meaning Range and Direction Finding but suggesting the already well-known Radio Direction Finding
Radio direction finder
A radio direction finder is a device for finding the direction to a radio source. Due to low frequency propagation characteristic to travel very long distances and "over the horizon", it makes a particularly good navigation system for ships, small boats, and aircraft that might be some distance...
.
In 1940 John Randall (physicist)
John Randall (physicist)
Sir John Turton Randall, FRS, FRSE, was a British physicist and biophysicist, credited with radical improvement of the cavity magnetron, an essential component of centimetric wavelength radar, which was one of the keys to the Allied victory in the Second World War. It is also the key component of...
and Harry Boot
Harry Boot
Henry Albert Howard "Harry" Boot was an English physicist who with Sir John Randall and James Sayers developed the cavity magnetron, which was one of the keys to the Allied victory in the Second World War.-Biography:...
developed the Cavity magnetron
Cavity magnetron
The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field. The 'resonant' cavity magnetron variant of the earlier magnetron tube was invented by John Randall and Harry Boot in 1940 at the University of...
which made one centimeter radar a reality. This device, the size of a small dinner plate, could be carried easily on aircraft and the short wavelength meant that the antenna would also be small and hence suitable for mounting on aircraft. The short wavelength and high power made it very effective at spotting submarines from the air.
Air Ministry
In March 1936 the work at Orfordness was moved to Bawdsey ManorBawdsey Manor
Bawdsey Manor stands at a prominent position at the mouth of the River Deben close to the village of Bawdsey in Suffolk, England, about 118 km northeast of London....
, nearby on the mainland. Until this time, the work had officially still been under the DSIR, but was now transferred to the Air Ministry. At the new Bawdsey Research Station, the CH equipment was assembled as a prototype. There were equipment problems when the Royal Air Force
Royal Air Force
The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...
(RAF) first exercised the prototype station in September 1936. These were cleared by the next April, and the Air Ministry started plans for a larger network of stations.
Initial hardware at CH stations was as follows: The transmitter operated on four pre-selected frequencies between 20 and 55 MHz, adjustable within 15 seconds, and delivered a peak power of 200 kW. The pulse duration was adjustable between 5 to 25 μs, with a repetition rate selectable as either 25 or 50 Hz. For synchronization of all CH transmitters, the pulse generator was locked to the 50 Hz of the British power grid. Four 360 feet (109.7 m) steel towers supported transmitting antennas, and four 240 feet (73.2 m) wooden towers supported cross-dipole arrays at three different levels. A goniometer
Goniometer
A goniometer is an instrument that either measures an angle or allows an object to be rotated to a precise angular position. The term goniometry is derived from two Greek words, gōnia, meaning angle, and metron, meaning measure....
was used to improve the directional accuracy from the multiple receiving antennas.
By the summer of 1937, 20 initial CH stations were in check-out operation. A major RAF exercise was performed before the end of the year, and was such a success that £10,000,000 was appropriated by the Treasury for an eventual full chain of coastal stations. At the start of 1938, the RAF took over control of all CH stations, and the network began regular operations.
In May 1938, Rowe replaced Watson Watt as Superintendent at Bawdsey. In addition to the work on CH and successor systems, there was now major work in airborne RDF equipment. This was led by E. G. Bowen and centered on 200-MHz (1.5 m) sets. The higher frequency allowed smaller antennas, appropriate for aircraft installation.
From the initiation of RDF work at Orfordness, the Air Ministry had kept the British Army and the Royal Navy generally informed; this led to both of these forces having their own RDF developments.
British Army
In 1931, at the at the Woolwich Research Station of the Army’s Signals Experimental Establishment (SEE), W. A. S. ButementW. A. S. Butement
William Alan Stewart Butement , was a defence scientist and public servant. A native of New Zealand, he made extensive contributions to radar development in Great Britain during World War II, served as the first chief scientist for the Australian Defence Scientific Service, then ended his...
and P. E. Pollard had examined pulsed 600 MHz (50-cm) signals for detection of ships. Although they prepared a memorandum on this subject and performed preliminary experiments, for undefined reasons the War Office did not give it consideration.
As the Air Ministry’s work on RDF progressed, Colonel Peter Worlledge of the Royal Engineer and Signals Board met with Watson Watt and was briefed on the RDF equipment and techniques being developed at Orfordness. His report, “The Proposed Method of Aeroplane Detection and Its Prospects,” led the SEE to set up an “Army Cell” at Bawdsey in October 1936. This was under E. Talbot Paris and the staff included Butement and Pollard. The Cell’s work emphasize two general types of RDF equipment: gun-laying (GL) systems for assisting anti-aircraft guns and searchlights, and coastal- defense (CD) systems for directing coastal artillery and defense of Army bases overseas.
Pollard led the first project, a gun-laying RDF code-named Mobile Radio Unit (MRU). This truck-mounted system was designed a small version of a CH station. It operated at 23 MHz (13 m) with a power of 300 kW. A single 105 feet (32 m) tower supported a transmitting antenna, as well as two receiving antennas set orthogonally for estimating the signal bearing. In February 1937, a developmental unit detected an aircraft at 60 m (96 km) range. The Air Ministry also adopted this system as a mobile auxiliary to the CH system.
In early 1938, Butement started the development of a CD system based on Bowen’s evolving 200-MHz (1.5-m) airborne sets. The transmitter had a 400 Hz pulse rate, a 2-μs pulse width, and 50 kW power (later increased to 150 kW). Although many of Bowen’s transmitter and receiver components were used, the system would not be airborne so there were no limitations on antenna size.
Primary credit for introducing beamed RDF systems in Great Britain must be given to Butement. For the CD, he developed a large dipole array, 10 feet (3 m) high and 24 feet (7.3 m) wide, giving much narrower beams and higher gain. This could be rotated at a speed up to 1.5 revolutions per minute. For greater directional accuracy, lobe switching
Lobe switching
Lobe switching is a method used on early radar sets to improve tracking accuracy. It used two slightly separated antenna elements to send the beam slightly to either side of the midline of the antenna, switching between the two to find which one gave the stronger return, thereby indicating which...
on the receiving antennas was adopted. As a part of this development, he formulated the first – at least in Great Britain – mathematical relationship that would later become well known as the “radar range equation.”
By May 1939, the CD RDF could detect aircraft flying as low as 500 feet (152.4 m) and at a range of 25 mi (40.2 km). With an antenna 60 feet (18.3 m) above sea level, it could determine the range of a 2,000-ton ship at 24 mi (38.6 km) and with an angular accuracy of as little as a quarter of a degree.
Royal Navy
Although the Royal Navy maintained close contact with the Air Ministry work at Bawdsey, they chose to establish their own RDF development at the Experimental Department of His Majesty’s Signal School (HMSS) in PortsmouthPortsmouth
Portsmouth is the second largest city in the ceremonial county of Hampshire on the south coast of England. Portsmouth is notable for being the United Kingdom's only island city; it is located mainly on Portsea Island...
, Hampshire
Hampshire
Hampshire is a county on the southern coast of England in the United Kingdom. The county town of Hampshire is Winchester, a historic cathedral city that was once the capital of England. Hampshire is notable for housing the original birthplaces of the Royal Navy, British Army, and Royal Air Force...
, on the south coast.
The HMSS started RDF work in September 1935. Initial efforts, under R. F. Yeo, were in wavelengths ranging between 75 MHz (4 m) and 1.2 GHz (25 cm). All of the work was under the utmost secrecy; it could not even be discussed with other scientists and engineers at Portsmouth. A 75 MHz range-only set was eventually developed and designated Type 79X. Basic tests were done using a training ship, but the operation was unsatisfactory.
In August 1937, the RDF development at the HMSS changed, with many of their best researchers brought into the activity. John D. S. Rawlinson was made responsible for improving the Type 79X. To increase the efficiency, he decreased the frequency to 43 MHz (7 m). Designated Type 79Y, it had separate, stationary transmitting and receiving antennas.
Prototypes of the Type 79Y air-warning system were successfully tested at sea in early 1938. The detection range on aircraft was between 30 and 50 mi (48 and 80 km), depending on height. The systems were then placed into service in August on the cruiser HMS Sheffield
HMS Sheffield (C24)
HMS Sheffield was one of the Southampton sub class of the Town-class cruisers of the Royal Navy during the Second World War. She took part in actions against several major German warships. Unlike most Royal Navy ships of her time, her fittings were constructed from stainless steel instead of the...
and in October on the battleship HMS Rodney. These were the first vessels in the Royal Navy with RDF systems.
Germany
A radio-based device for remotely indicating the presence of ships was built in Germany by Christian Hülsmeyer in 1904. Often referred to as the first radar system, this did not directly measure the range (distance) to the target, and thus did not meet the criteria to be given this name.Over the following three decades in invention-rich Germany, a number of radio-based detection systems were developed, but none were true radars. This situation changed as World War II loomed closer. Developments in three leading industries are described.
GEMA
In the early 1930s, physicist Rudolf KühnholdRudolf Kühnhold
Rudolf Kühnhold was an experimental physicist who is often given credit for initiating research that led to the Funkmessgerät in Germany.-Early life:...
, Scientific Director at the Kriegsmarine
Kriegsmarine
The Kriegsmarine was the name of the German Navy during the Nazi regime . It superseded the Kaiserliche Marine of World War I and the post-war Reichsmarine. The Kriegsmarine was one of three official branches of the Wehrmacht, the unified armed forces of Nazi Germany.The Kriegsmarine grew rapidly...
(German Navy) Nachrichtenmittel-Versuchsanstalt (NVA—Experimental Institute of Communication Systems) in Kiel
Kiel
Kiel is the capital and most populous city in the northern German state of Schleswig-Holstein, with a population of 238,049 .Kiel is approximately north of Hamburg. Due to its geographic location in the north of Germany, the southeast of the Jutland peninsula, and the southwestern shore of the...
, was attempting to improve the acoustical methods of underwater detection of ships. He concluded that the desired accuracy in measuring distance to targets could be attained only by using pulsed electromagnetic waves.
During 1933, Kühnhold first attempted to test this concept with a transmitting and receiving set that operated in the microwave
Microwave
Microwaves, a subset of radio waves, have wavelengths ranging from as long as one meter to as short as one millimeter, or equivalently, with frequencies between 300 MHz and 300 GHz. This broad definition includes both UHF and EHF , and various sources use different boundaries...
region at 13.5 cm (2.22 GHz). The transmitter used a Barkhausen-Kurz tube
Barkhausen-Kurz tube
The Barkhausen-Kurz tube, also called the B-K oscillator, was commonly used in early electronic systems operating in the ultra-high frequency portion of the radio spectrum.-Development:...
(the first microwave generator) that produced only 0.1 watt. Unsuccessful with this, he asked for assistance from Paul-Gunther Erbslöh and Hans-Karl Freiherr von Willisen, amateur radio operators who were developing a VHF system for communications. They enthusiastically agreed, and in January 1934, formed a company, Gesellschaft für Elektroakustische und Mechanische Apparate ((GEMA)), for the effort. From the start, the firm was always called simply GEMA.
Work on a Funkmessgerät für Untersuchung (radio measuring device for reconnaissance) began in earnest at GEMA. Hans Hollmann
Hans Hollmann
Hans Erich Hollmann was a German electronic specialist who made several breakthroughs in the development of radar....
and Theodor Schultes, both affiliated with the prestigious Heinrich Hertz Institute in Berlin
Berlin
Berlin is the capital city of Germany and is one of the 16 states of Germany. With a population of 3.45 million people, Berlin is Germany's largest city. It is the second most populous city proper and the seventh most populous urban area in the European Union...
, were added as consultants. The first apparatus used a split-anode magnetron purchased from Philips
Philips
Koninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....
in the Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
. This provided about 70 W at 50 cm (600 MHz), but suffered from frequency instability. Hollmann built a regenerative
Regenerative circuit
The regenerative circuit or "autodyne" allows an electronic signal to be amplified many times by the same vacuum tube or other active component such as a field effect transistor. It consists of an amplifying vacuum tube or transistor with its output connected to its input through a feedback...
receiver and Schultes developed Yagi antenna
Yagi antenna
A Yagi-Uda array, commonly known simply as a Yagi antenna, is a directional antenna consisting of a driven element and additional parasitic elements...
s for transmitting and receiving. In June 1934, large vessels passing through the Kiev Harbor were detected by Doppler-beat interference at a distance of about 2 km (1.2 mi). In October, strong reflections were observed from an aircraft that happened to fly through the beam; this opened consideration of targets other than ships.
Kühnhold then shifted the GEMA work to a pulse-modulated system. A new 50 cm (600 MHz) Philips magnetron with better frequency stability was used. It was modulated with 2- μs
Microsecond
A microsecond is an SI unit of time equal to one millionth of a second. Its symbol is µs.A microsecond is equal to 1000 nanoseconds or 1/1000 millisecond...
pulses at a PRF of 2000 Hz. The transmitting antenna was an array of 10 pairs of dipoles with a reflecting mesh. The wide-band regenerative receiver used Acorn tubes from RCA, and the receiving antenna had three pairs of dipoles and incorporated lobe switching
Lobe switching
Lobe switching is a method used on early radar sets to improve tracking accuracy. It used two slightly separated antenna elements to send the beam slightly to either side of the midline of the antenna, switching between the two to find which one gave the stronger return, thereby indicating which...
. A blocking device (a duplexer), shut the receiver input when the transmitter pulsed. A Braun tube (a CRT) was used for displaying the range.
The equipment was first tested at a NVA site at the Lübecker Bay near Pelzerhaken. During May 1935, it detected returns from woods across the bay at a range of 15 km (9.3 mi). It had limited success, however, in detecting a research ship, Welle, only a short distance away. The receiver was then rebuilt, becoming a super-regenerative set with two intermediate-frequency stages. With this improved receiver, the system readily tracked vessels at up to 8 km (5 mi) range.
In September 1935, a demonstration was given to the Commander-in-Chief of the Kriegsmarine. The system performance was excellent; the range was read off the Braun tube with a tolerance of 50 meters (less than 1 percent variance), and the lobe switching allowed a directional accuracy of 0.1 degree. Historically, this marked the first naval vessel equipped with radar. Although this apparatus was not put into production, GEMA was funded to develop similar systems operating around 50 cm (500 MHz). These became the Seetakt for the Kriegsmarine and the Freya
Freya radar
Freya was an early warning radar deployed by Germany during World War II, named after the Norse Goddess Freyja. During the war over a thousand stations were built. A naval version operating on a slightly different wavelength was also developed as Seetakt...
for the Luftwaffe (German Air Force).
Kühnhold remained with the NVA but also consulted with GEMA. He is considered by many in Germany as the Father of Radar. During 1933-6, Hollmann wrote the first comprehensive treatise on microwaves, Physik und Technik der ultrakurzen Wellen (Physics and Technique of Ultrashort Waves), Springer 1938.
Telefunken
In 1933, when Kühnhold at the NVA was first experimenting with microwaves, he had sought information from TelefunkenTelefunken
Telefunken is a German radio and television apparatus company, founded in Berlin in 1903, as a joint venture of Siemens & Halske and the Allgemeine Elektricitäts-Gesellschaft...
on microwave tubes. (Telefunken was the largest supplier of radio products in Germany) There, Wilhelm Tolmé Runge
Wilhelm Runge
Wilhelm Tolmé Runge was an electrical engineer and physicist who had a major involvement in developing radar systems in Germany.-Early life:...
had told him that no vacuum tubes were available for these frequencies. In fact, Runge was already experimenting with high-frequency transmitters and had Telefunken’s tube department working on cm-wavelength devices.
In the summer of 1935, Runge, now Director of Telefunken’s Radio Research Laboratory, initiated an internally funded project in radio-based detection. Using Barkhausen-Kurz tubes, a 50 cm (600 MHz) receiver and 0.5-W transmitter were built. With the antennas placed flat on the ground some distance apart, Runge arranged for an aircraft to fly overhead and found that the receiver gave a strong Doppler-beat interference signal.
Runge, now with Hans Hollmann as a consultant, continued in developing a 1.8 m (170 MHz) system using pulse-modulation. Wilhelm Stepp developed a transmit-receive device (a duplexer) for allowing a common antenna. Stepp also code-named the system Darmstadt after his home town, starting the practice in Telefunken of giving the systems names of cities. The system, with only a few watts transmitter power, was first tested in February 1936, detecting an aircraft at about 5 km (3.1 mi) distance. This led the Luftwaffe to fund the development of a 50 cm (600 MHz) gun-laying system, the Würzburg.
Lorenz
Since before the First World War, Standard Elektrik Lorenz had been the main supplier of communication equipment for the German military and was the main rival of Telefunken. In late 1935, when Lorenz found that Runge at Telefunken was doing research in radio-based detection equipment, they started a similar activity under Gottfried Müller. A pulse-modulated set called Einheit für Abfragung (DFA - Device for Detection) was built. It used a type DS-310 tube (similar to the Acorn) operating at 70 cm (430 MHz) and about 1 kW power, it had identical transmitting and receiving antennas made with rows of half-wavelength dipoles backed by a reflecting screen.In early 1936, initial experiments gave reflections from large buildings at up to about 7 km (4.3 mi). The power was doubled by using two tubes, and in mid-1936, the equipment was set up on cliffs near Kiel, and good detections of ships at 7 km (4.3 mi) and aircraft at 4 km (2.5 mi) were attained.
The success of this experimental set was reported to the Kriegsmarine, but they showed no interest; they were already fully engaged with GEMA for similar equipment. Also, because of extensive agreements between Lorenz and many foreign countries, the naval authorities had reservations concerning the company handling classified work. The DFA was then demonstrated to the Heer (German Army), and they contracted with Lorenz for developing Kurfürst (Cure prince), a system for supporting Flugzeugabwehrkanone (Flak, anti-aircraft guns).
USSR
In 1895, Alexander Stepanovich PopovAlexander Stepanovich Popov
Alexander Stepanovich Popov was a Russian physicist who was the first person to demonstrate the practical application of electromagnetic waves....
, a physics instructor at the Imperial Russian Navy
Imperial Russian Navy
The Imperial Russian Navy refers to the Tsarist fleets prior to the February Revolution.-First Romanovs:Under Tsar Mikhail Feodorovich, construction of the first three-masted ship, actually built within Russia, was completed in 1636. It was built in Balakhna by Danish shipbuilders from Holstein...
school in Kronstadt
Kronstadt
Kronstadt , also spelled Kronshtadt, Cronstadt |crown]]" and Stadt for "city"); is a municipal town in Kronshtadtsky District of the federal city of St. Petersburg, Russia, located on Kotlin Island, west of Saint Petersburg proper near the head of the Gulf of Finland. Population: It is also...
, developed an apparatus using a coherer
Coherer
The coherer was a primitive form of radio signal detector used in the first radio receivers during the wireless telegraphy era at the beginning of the twentieth century. Invented around 1890 by French scientist Édouard Branly, it consisted of a tube or capsule containing two electrodes spaced a...
tube for detecting distant lightning strikes. The next year, he added a spark-gap transmitter
Spark-gap transmitter
A spark-gap transmitter is a device for generating radio frequency electromagnetic waves using a spark gap.These devices served as the transmitters for most wireless telegraphy systems for the first three decades of radio and the first demonstrations of practical radio were carried out using them...
and demonstrated the first radio communication set in Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
. During 1897, while testing this in communicating between two ships in the Baltic Sea
Baltic Sea
The Baltic Sea is a brackish mediterranean sea located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and...
, he took note of an interference beat caused by the passage of a third vessel. In his report, Popov wrote that this phenomenon might be used for detecting objects, but he did nothing more with this observation.
In a few years following the 1917 Russian Revolution and the establishment the Union of Soviet Socialist Republics (USSR or Soviet Union) in 1924, Germany’s Luftwaffe
Luftwaffe
Luftwaffe is a generic German term for an air force. It is also the official name for two of the four historic German air forces, the Wehrmacht air arm founded in 1935 and disbanded in 1946; and the current Bundeswehr air arm founded in 1956....
had aircraft capable of penetrating deep into Soviet territory. Thus, the detection of aircraft at night or above clouds was of great interest to the Voiska Protivo-vozdushnoi aborony (PVO, Air Defense Forces) of the Raboche-Krest'yanskaya Krasnaya Armiya (RKKA, Workers’–Peasants’ Red Army
Red Army
The Workers' and Peasants' Red Army started out as the Soviet Union's revolutionary communist combat groups during the Russian Civil War of 1918-1922. It grew into the national army of the Soviet Union. By the 1930s the Red Army was among the largest armies in history.The "Red Army" name refers to...
).
The PVO depended on optical devices for locating targets, and had physicist Pavel K. Oshchepkov
Pavel K. Oshchepkov
Pavel Kondratyevich Oshchepkov was a Russian physicist who had a leading role in the development of radio-location in the USSR. During the Great Purge he was sent to a Gulag labor camp for 10 years...
conducting research in possible improvement of these devices. In June 1933, Oshchepkov changed his research from optics to radio techniques and started the development of a razvedyvlatl’naya elektromagnitnaya stantsiya (reconnaissance electromagnetic station). In a short time, Oshchepkov was made responsible for a PVO experino-tekknicheskii sektor (technical expertise sector) devoted to radiolokatory (radio-location) techniques as well as heading a Special Construction Bureau (SCB) in Leningrad
Leningrad
Leningrad is the former name of Saint Petersburg, Russia.Leningrad may also refer to:- Places :* Leningrad Oblast, a federal subject of Russia, around Saint Petersburg* Leningrad, Tajikistan, capital of Muminobod district in Khatlon Province...
(formerly St. Petersberg).
Radio-Location Beginnings
The Glavnoe artilkeriisko upravlenie (GAU, Main Artillery Administration) was considered the “brains” of the Red Army. It not only had competent engineers and physicists on its central staff, but also had a number of scientific research institutes. Thus, the GAU was also assigned the aircraft detection problem, and Lt. Gen. M. M. Lobanov was placed in charge.After examining existing optical and acoustical equipment, Lobanov also turned to radio-location techniques. For this he approached the Tsentral’naya radiolaboratoriya (TsRL, Central Radio Laboratory) in Leningrad. Here, Yu. K. Korovin was conducting research on VHF communications, and had built a 50 cm (600 MHz), 0.2 W transmitter using a Barkhausen-Kurz tube
Barkhausen-Kurz tube
The Barkhausen-Kurz tube, also called the B-K oscillator, was commonly used in early electronic systems operating in the ultra-high frequency portion of the radio spectrum.-Development:...
. For testing the concept, Korovin arranged the transmitting and receiving antennas along the flight path of an aircraft. On January 3, 1934, a Doppler
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
signal was received by reflections from the aircraft at some 600 m range and 100–150 m altitude.
For further research in detection methods, a major conference on this subject was arranged for the PVO by the Rossiiskaya Akademiya Nauk (RAN, Russian Academy of Sciences
Russian Academy of Sciences
The Russian Academy of Sciences consists of the national academy of Russia and a network of scientific research institutes from across the Russian Federation as well as auxiliary scientific and social units like libraries, publishers and hospitals....
). The conference was held in Leningrad in mid-January, 1934, and chaired by Abram Fedorovich Ioffe, Director of the Leningrad Physical-Technical Institute (LPTI). Ioffe was generally considered the top Russian physicist of his time. All types of detection techniques were discussed, but radio-location received the greatest attention.
To distribute the conference findings to a wider audience, the proceedings were published the following month in a journal. This included all of the then-existing information on radio-location in the USSR, available (in Russian language) to researchers in this field throughout the world.
Recognizing the potential value of radio-location to the military, the GAU made a separate agreement with the Leningrad Electro-Physics Institute (LEPI), for a radio-location system. This technical effort was led by B. K. Shembel. The LEPI had built a transmitter and receiver to study the radio-reflection characteristics of various materials and targets. Shemlbel readily made this into an experimental bi-static
Bistatic radar
Bistatic radar is the name given to a radar system which comprises a transmitter and receiver which are separated by a distance that is comparable to the expected target distance. Conversely, a radar in which the transmitter and receiver are collocated is called a monostatic radar...
radio-location system called Bistro (Rapid).
The Bistro transmitter, operating at 4.7 m (64 MHz), produced near 200 W and was frequency-modulated by a 1 kHz tone. A fixed transmitting antenna gave a broad coverage of what was called a radiozkzn (radio screen). A regenerative
Regenerative circuit
The regenerative circuit or "autodyne" allows an electronic signal to be amplified many times by the same vacuum tube or other active component such as a field effect transistor. It consists of an amplifying vacuum tube or transistor with its output connected to its input through a feedback...
receiver, located some distance from the transmitter, had a dipole antenna mounted on a hand-driven reciprocating mechanism. An aircraft passing into the screened zone would reflect the radiation, and the receiver would detect the Doppler-interference beat between the transmitted and reflected signals.
Bistro was first tested during the summer of 1934. With the receiver up to 11 km away from the transmitter, the set could only detect an aircraft entering a screen at about 3 km (1.9 mi) range and a under 1,000 m. With improvements, it was believed to have a potential range of 75 km, and five sets were ordered in October for field trials. Bistro is often cited as the USSR’s first radar system; however, it was incapable of directly measuring range and thus could not be so classified.
LEPI and TsRL were both made a part of Nauchno-issledovatel institut-9 (NII-9, Scientific Research Institute #9), a new GAU organization opened in Leningrad in 1935. Mikhail A. Bonch-Bruyevich, a renowned radio physicist previously with TsRL and the University of Leningrad, was named the NII-9 Scientific Director.
Research on magnetrons began at Kharkov University in Ukraine
Ukraine
Ukraine is a country in Eastern Europe. It has an area of 603,628 km², making it the second largest contiguous country on the European continent, after Russia...
during the mid-1920s. Before the end of the decade this had resulted in publications with worldwide distribution, such as the German journal Annalen der Physik
Annalen der Physik
Annalen der Physik is one of the oldest physics journals worldwide. The journal publishes original, peer-reviewed papers in the areas of experimental, theoretical, applied and mathematical physics and related areas...
(Annals of Physics). Based on this work, Ioffe recommended that a portion of the LEPI be transferred to the city of Kharkov, resulting in the Ukrainian Institute of Physics and Technology (LIPT) being formed in 1930. Within the LIPT, the Laboratory of Electromagnetic Oscillations (LEMO), headed by Abram A. Slutskin
Abram A. Slutskin
Abram A. Slutskin was a Russian scientist and professor who had a major role in shaping radio science in the Soviet Union. He was a pioneer in cavity magnetron development and the application of these devices in radio-location systems....
, continued with magnetron development. Led by Aleksandr S. Usikov, a number of advanced segmented-anode magnetrons evolved. (It is noted that these and other early magnetrons developed in the USSR suffered from frequency instability, a problem in their use in Soviet radar systems.)
In 1936, one of Usikov’s magnetrons producing about 7 W at 18 cm (1.7 GHz) was used by Shembel at the NII-9 as a transmitter in a radioiskatel (radio-seeker) called Burya (Storm). Operating similarly to Bistro, the range of detection was about 10 km, and provided azimuth and elevation coordinates estimated to within 4 degrees. No attempts were made to make this intro a pulsed system, thus, it could not provide range and was not qualified to be classified as a radar. It was, however, the first microwave radio-detection system.
While work by Shembel and Bonch-Bruyevich on continuous-wave systems was taking place at NII-9, Oshehepkov at the SCB and V. V. Tsimbalin of Ioffe’s LPTI were pursuing a pulsed system. In 1936, they built a radio-location set operating at 4 m (75 MHz) with a peak-power of about 500 W and a 10-μs pulse duration. Before the end of the year, tests using separated transmitting and receiving sites resulted in an aircraft being detected at 7 km. In April 1937, with the peak-pulse power increased to 1 kW and the antenna separation also increased, test showed a detection range of near 17 km at a height of 1.5 km. Although a pulsed system, it was not capable of directly providing range – the technique of using pulses for determining range had not yet been developed.
Pre-War Radio-Location Systems
In June 1937, all of the work in Leningrad on radio-location suddenly stopped. The infamous Great PurgeGreat Purge
The Great Purge was a series of campaigns of political repression and persecution in the Soviet Union orchestrated by Joseph Stalin from 1936 to 1938...
of dictator Joseph Stalin
Joseph Stalin
Joseph Vissarionovich Stalin was the Premier of the Soviet Union from 6 May 1941 to 5 March 1953. He was among the Bolshevik revolutionaries who brought about the October Revolution and had held the position of first General Secretary of the Communist Party of the Soviet Union's Central Committee...
swept over the military high commands and its supporting scientific community. The PVO chief was executed. Oshchepkov, charged with “high crime,” was sentenced to 10 years at a Gulag
Gulag
The Gulag was the government agency that administered the main Soviet forced labor camp systems. While the camps housed a wide range of convicts, from petty criminals to political prisoners, large numbers were convicted by simplified procedures, such as NKVD troikas and other instruments of...
penal labor camp. NII-9 as an organization was saved, but Shenbel was dismissed and Bonch-Bruyevich was named the new director.
The Nauchnoissledovatel skii ispytalel nyi institut suyazi RKKA (NIIIS-KA, Scientific Research Institute of Signals of the Red Army), had initially opposed research in radio-location, favoring instead acoustical techniques. However, this portion of the Red Army gained power as a result of the Great Purge, and did an about face, pressing hard for speedy development of radio-location systems. They took over Oshchepkov’s laboratory and were made responsible for all existing and future agreements for research and factory production.
Writing later about the Purge and subsequent effects, General Lobanov commented that it led to the development being placed under a single organization, and the rapid reorganization of the work to accomplish needed results.
At Oshchepkov’s former laboratory, work with the 4 m (75 MHz) pulsed-transmission system was continued by A. I. Shestako. Through pulsing, the transmitter produced a peak power of 1 kW, the highest level thus far generated. In July 1938, a fixed-position, bi-static experimental system detected an aircraft at about 30 km range at heights of 500 m, and at 95 km range, for high-flying targets at 7.5 km altitude. The system was still incapable of directly determining the range.
The project was then taken up by Ioffe’s LPTI, resulting in the development of a mobile system designated Redut (Redoubt). An arrangement of new transmitter tubes was used, giving near 50 kW peak-power with a 10 μs pulse-duration. Yagi
Yagi antenna
A Yagi-Uda array, commonly known simply as a Yagi antenna, is a directional antenna consisting of a driven element and additional parasitic elements...
antennas were adopted for both transmitting and receiving.
The Redut was first field tested in October 1939, at a site near Sevastopol
Sevastopol
Sevastopol is a city on rights of administrative division of Ukraine, located on the Black Sea coast of the Crimea peninsula. It has a population of 342,451 . Sevastopol is the second largest port in Ukraine, after the Port of Odessa....
, a port in Ukraine on the coast of the Black Sea
Black Sea
The Black Sea is bounded by Europe, Anatolia and the Caucasus and is ultimately connected to the Atlantic Ocean via the Mediterranean and the Aegean seas and various straits. The Bosphorus strait connects it to the Sea of Marmara, and the strait of the Dardanelles connects that sea to the Aegean...
. This testing was in part to show the NKKF (Soviet Navy) the value of early-warning radio-location for protecting strategic ports. With the equipment on a cliff about 160 meters above sea level, a flying boat was detected at ranges up to 150 km. The Yagi antennas were spaced about 1,000 meters; thus, close coordination was required to aim them in synchronization.
At the NII-9 under Bonch-Bruyevich, scientists developed two types of very advanced microwave generators. In 1938, a linear-beam, velocity-modulated vacuum tube (a klystron
Klystron
A klystron is a specialized linear-beam vacuum tube . Klystrons are used as amplifiers at microwave and radio frequencies to produce both low-power reference signals for superheterodyne radar receivers and to produce high-power carrier waves for communications and the driving force for modern...
) was developed by Nikolay Devyatkov
Nikolay Devyatkov
Nikolay Devyatkov — was a Soviet/Russian scientist and inventor of microwave vacuum tubes and medical equipment. Full Member of the USSR/Russian Academy of Sciences . Professor of the Moscow Institute of Physics and Technology.Most Devyatkov's scientific papers apply to a microwave vacuum tubes...
, based on designs from Kharkpv. This device produced about 25 W at 15–18 cm (2.0–1.7 GHz) and was later used in experimental systems. Devyatkov followed this with a simpler, single-resonator device (a reflex klystron). At this same time, D. E. Malyarov and N. F. Alekseyev were building a series of magnetrons, also based on designs from Kharkov; the best of these produced 300 W at 9 cm (3 GHz).
Also at NII-9, D. S. Stogov was placed in charge of the improvements to the Bistro system. Redesignated as Reven (Rhubarb), it was tested in August 1938, but was only marginally better than the predecessor. With additional minor operational improvements, it was made into a mobile system called Radio Ulavlivatel Samoletov (RUS, Radio Catcher of Aircraft), soon designated as RUS-1. This continuous-wave, bi-static system had a truck-mounted transmitter operating at 4.7 m (64 MHz) and two truck-mounted receivers.
Although the RUS-1 transmitter was in a cabin on the rear of a truck, the antenna had to be strung between external poles anchored to the ground. A second truck carrying the electrical generator and other equipment was backed against the transmitter truck. Two receivers were used, each in a truck-mounted cabin with a dipole antenna on a rotatable pole extended overhead. In use, the receiver trucks were placed about 40 km apart; thus, with two positions, it would be possible to make a rough estimate of the range by triangulation
Triangulation
In trigonometry and geometry, triangulation is the process of determining the location of a point by measuring angles to it from known points at either end of a fixed baseline, rather than measuring distances to the point directly...
on a map.
The RUS-1 system was tested and put into production in 1939, then entered service in 1940, becoming the first deployed radio-location system in the Red Army. A total of about 45 RUS-1 systems were built at the Svetlana Factory in Leningrad before the end of 1941, and deployed along the western USSR borders and in the Far East. Without direct ranging capability, however, the military found the RUS-1 to be of little value.
Even before the demise of efforts in Leningrad, the NIIIS-KA had contracted with the UIPT in Kharkov to investigate a pulsed radio-location system for anti-aircraft applications. This led the LEMO, in March 1937, to start an internally funded project with the code name Zenit (a popular football team at the time). The transmitter development was led by Usikov, supplier of the magnetron used earlier in the Burya. For the Zenit, Usikov used a 60 cm (500 MHz) magnetron pulsed at 10–20 μs duration and providing 3 kW pulsed power, later increased to near 10 kW. Semion Braude
Semion Braude
Semion Yakovlevich Braude was a Ukrainian physicist and radio astronomer.Of Ashkenazi Jewish descent, Buaude was born in Poltava, Ukraine, and pursued his higher education at the Kharkov University , receiving his undergraduate degree from the Physics and Mathematics Department in 1932...
led the development of a superheterodyne receiver
Superheterodyne receiver
In electronics, a superheterodyne receiver uses frequency mixing or heterodyning to convert a received signal to a fixed intermediate frequency, which can be more conveniently processed than the original radio carrier frequency...
using a tunable magnetron as the local oscillator
Local oscillator
A local oscillator is an electronic device used to generate a signal normally for the purpose of converting a signal of interest to a different frequency using a mixer. This process of frequency conversion, also referred to as heterodyning, produces the sum and difference frequencies of the...
. The system had separate transmitting and receiving antennas set about 65 m apart, built with dipoles backed by 3-meter parabolic reflectors.
Zenit was first tested in October 1938. In this, a medium-sized bomber was detected at a range of 3 km. The testing was observed by the NIIIS-KA and found to be sufficient for starting a contracted effort. An agreement was made in May 1939, specifying the required performance and calling for the system to be ready for production by 1941. The transmitter was increased in power, the antennas had selsens added to allow them to track, and the receiver sensitivity was improved by using an RCA
RCA
RCA Corporation, founded as the Radio Corporation of America, was an American electronics company in existence from 1919 to 1986. The RCA trademark is currently owned by the French conglomerate Technicolor SA through RCA Trademark Management S.A., a company owned by Technicolor...
955 acorn triode as the local oscillator.
A demonstration of the improved Zenit was given in September 1940. In this, it was shown that the range, altitude, and azimuth of an aircraft flying at heights between 4,000 and 7,000 meters could be determined at up to 25 km distance. The time required for these measurements, however, was about 38 seconds, far too long for use by anti-aircraft batteries. Also, with the antennas aimed at a low angle, there was a dead zone of some distance caused by interference from ground-level reflections. While this performance was not satisfactory for immediate gun-laying applications, it was the first full three-coordinate radio-location system in the Soviet Union and showed the way for future systems.
Work at the LEMO continued on Zenit, particularly in converting it into a single-antenna system designated Rubin. This effort, however, was disrupted by the invasion of the USSR by Germany in June 1941. In a short while, the development activities at Kharkov were ordered to be evacuated into the Far East. The research efforts in Leningrad were similarly dispersed.
After eight years of effort by highly qualified physicists and engineers, the USSR entered World War II without a fully developed and fielded radar system.
Japan
As a sea-faring nation, Japan had an early interest in wireless (radio) communications. The first known use of wireless telegraphyWireless telegraphy
Wireless telegraphy is a historical term used today to apply to early radio telegraph communications techniques and practices, particularly those used during the first three decades of radio before the term radio came into use....
in warfare at sea was by the Imperial Japanese Navy
Imperial Japanese Navy
The Imperial Japanese Navy was the navy of the Empire of Japan from 1869 until 1947, when it was dissolved following Japan's constitutional renunciation of the use of force as a means of settling international disputes...
, in defeating the Russian Imperial Fleet in 1904. There was an early interest in equipment for radio direction-finding, for use in both navigation and military surveillance. The Imperial Navy developed an excellent receiver for this purpose in 1921, and soon most of the Japanese warships had this equipment.
In the two decades between the two World Wars, radio technology in Japan made advancements on a par with that in the western nations. There were often impediments, however, in transferring these advancements into the military. For a long time, the Japanese had believed they had the best fighting capability of any military force in the world. The military leaders, who were then also in control of the government, sincerely felt that the weapons, aircraft, and ships that they had built were fully sufficient and, with these as they were, the Japanese Army and Navy were invincible. In 1936, Japan joined Nazi Germany
Nazi Germany
Nazi Germany , also known as the Third Reich , but officially called German Reich from 1933 to 1943 and Greater German Reich from 26 June 1943 onward, is the name commonly used to refer to the state of Germany from 1933 to 1945, when it was a totalitarian dictatorship ruled by...
and Fascist Italy
Italian Fascism
Italian Fascism also known as Fascism with a capital "F" refers to the original fascist ideology in Italy. This ideology is associated with the National Fascist Party which under Benito Mussolini ruled the Kingdom of Italy from 1922 until 1943, the Republican Fascist Party which ruled the Italian...
in a Tripartite Pact
Tripartite Pact
The Tripartite Pact, also the Three-Power Pact, Axis Pact, Three-way Pact or Tripartite Treaty was a pact signed in Berlin, Germany on September 27, 1940, which established the Axis Powers of World War II...
.
Technology Background
Radio engineering was strong in Japan’s higher education institutions, especially the Imperial (government-financed) universities. This included undergraduate and graduate study, as well as academic research in this field. Special relationships were established with foreign universities and institutes, particularly in Germany, with Japanese teachers and researchers often going overseas for advanced study.The academic research tended toward the improvement of basic technologies, rather than their specific applications. There was considerable research in high-frequency and high-power oscillators, such as the magnetron
Cavity magnetron
The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field. The 'resonant' cavity magnetron variant of the earlier magnetron tube was invented by John Randall and Harry Boot in 1940 at the University of...
, but the application of these devices was generally left to industrial and military researchers.
One of Japan’s best-known radio researchers in the 1920s-30s era was Professor Hidetsugu Yagi
Hidetsugu Yagi
Hidetsugu Yagi was a Japanese electrical engineer. When working at Tohoku University, he wrote several important articles that introduced a new antenna design by his colleague Shintaro Uda to the English-speaking world.The Yagi antenna, patented in 1926, allows directional communication using...
. After graduate study in Germany, England, and America, Yagi joined Tohoku University where his research centered on antennas and oscillators for high-frequency communications. A summary of the radio research work at Tohoku University was contained in a 1928 seminal paper by Yagi.
Jointly with Shintaro Uda
Shintaro Uda
Japanese inventor. Assistant of professor Hidetsugu Yagi at Tohoku University, where they invented the Yagi-Uda antenna in 1926. In February 1926, Yagi and Uda published their first report on the wave projector antenna in a Japanese publication. Yagi applied for patents on the new antenna both in...
, one Yagi’s first doctoral students, a radically new antenna emerged. It had a number of parasitic elements (directors and reflectors) and would come to be known as the Yagi-Uda or Yagi antenna
Yagi antenna
A Yagi-Uda array, commonly known simply as a Yagi antenna, is a directional antenna consisting of a driven element and additional parasitic elements...
. A U.S. patent, issued in May 1932, was assigned to RCA
RCA
RCA Corporation, founded as the Radio Corporation of America, was an American electronics company in existence from 1919 to 1986. The RCA trademark is currently owned by the French conglomerate Technicolor SA through RCA Trademark Management S.A., a company owned by Technicolor...
. To this day, this is the most widely used directional antenna
Directional antenna
A directional antenna or beam antenna is an antenna which radiates greater power in one or more directions allowing for increased performance on transmit and receive and reduced interference from unwanted sources....
worldwide.
The cavity magnetron
Cavity magnetron
The cavity magnetron is a high-powered vacuum tube that generates microwaves using the interaction of a stream of electrons with a magnetic field. The 'resonant' cavity magnetron variant of the earlier magnetron tube was invented by John Randall and Harry Boot in 1940 at the University of...
was also of interest to Yagi. This HF
High frequency
High frequency radio frequencies are between 3 and 30 MHz. Also known as the decameter band or decameter wave as the wavelengths range from one to ten decameters . Frequencies immediately below HF are denoted Medium-frequency , and the next higher frequencies are known as Very high frequency...
(~10-MHz) device had been invented in 1921 by Albert W. Hull at General Electric
General Electric
General Electric Company , or GE, is an American multinational conglomerate corporation incorporated in Schenectady, New York and headquartered in Fairfield, Connecticut, United States...
, and Yagi was convinced that it could function in the VHF or even the UHF region. In 1927, Kinjiro Okabe
Kinjiro Okabe
was a Japanese electrical engineering researcher and professor who made major contributions to magnetron and radar development.One of Japan’s best-known radio researchers in the 1920s-30s era was Professor Hidetsugu Yagi, who was initially at Tohoku University. Kinjiro Okabe was one of Yagi’s first...
, another of Yagi’s early doctoral students, developed a split-anode device that ultimately generated oscillations at wavelengths down to about 12 cm (2.5 GHz).
Researchers at other Japanese universities and institutions also started projects in magnetron development, leading to improvements in the split-anode device. These included Kiyoshi Morita at the Tokyo Institute of Technology
Tokyo Institute of Technology
The Tokyo Institute of Technology is a public research university located in Greater Tokyo Area, Japan. Tokyo Tech is the largest institution for higher education in Japan dedicated to science and technology. Tokyo Tech enrolled 4,850 undergaraduates and 5006 graduate students for 2009-2010...
, and Tsuneo Ito at Tokoku University.
Shigeru Nakajima at Japan Radio Company
Japan Radio Company
is a Japanese company specialising in the field of wireless electronics for the communications industry.- History :Established in 1915, the company has produced a wide variety of products including marine electronics, measuring equipment for telecommunications, broadcast radio equipment, and...
(JRC) saw a commercial potential of these devices and began the further development and subsequent very profitable production of magnetrons for the medical dielectric heating
Dielectric heating
Dielectric heating, also known as electronic heating, RF heating, high-frequency heating and diathermy, is the process in which a high-frequency alternating electric field, or radio wave or microwave electromagnetic radiation heats a dielectric material. At higher frequencies, this heating is...
(diathermy) market. The only military interest in magnetrons was shown by Yoji Ito
Yoji Ito
was an engineer and scientist that had a major role in the Japanese development of magnetrons and the Radio Range Finder .-Early years:...
at the Naval Technical Research Institute (NTRI).
The NTRI was formed in 1922, and became fully operational in 1930. Located at Meguro, Tokyo
Meguro, Tokyo
is one of the 23 special wards of Tokyo, Japan. It calls itself Meguro City in English.Meguro hosts fifteen foreign embassies and consulates. One of Tokyo's most exclusive residential neighborhoods is located in Meguro....
, near the Tokyo Institute of Technology, first-rate scientists, engineers, and technicians were engaged in activities ranging from designing giant submarines to building new radio tubes. Included were all of the precursors of radar, but this did not mean that the heads of the Imperial Navy accepted these accomplishments.
In 1936, Tsuneo Ito (no relationship to Yoji Ito) developed an 8-split-anode magnetron that produced about 10 W at 10 cm (3 GHz). Based on its appearance, it was named Tachibana (or Mandarin, an orange citrus fruit). Tsuneo Ito also joined the NTRI and continued his research on magnetrons in association with Yoji Ito. In 1937, they developed the technique of coupling adjacent segments (called push-pull), resulting in frequency stability, an extremely important magnetron breakthrough.
By early 1939, NTRI/JRC had jointly developed a 10-cm (3-GHz), stable-frequency Mandarin-type magnetron (No. M3) that, with water cooling, could produce 500-W power. In the same time period, magnetrons were built with 10 and 12 cavities operating as low as 0.7 cm (40 GHz). The configuration of the M3 magnetron was essentially the same as that used later in the magnetron developed by Boot and Randall
Harry Boot
Henry Albert Howard "Harry" Boot was an English physicist who with Sir John Randall and James Sayers developed the cavity magnetron, which was one of the keys to the Allied victory in the Second World War.-Biography:...
at Birmingham University in early 1940, including the improvement of strapped cavities. Unlike the high-power magnetron in Great Britain, however, the initial device from the NTRI generated only a few hundred watts.
In general, there was no lack of scientific and engineering capabilities in Japan; their warships and aircraft clearly showed high levels of technical competency. They were ahead of Great Britain in the development of magnetrons, and their Yagi antenna was the world standard for VHF systems. It was simply that the top military leaders failed to recognize how the application of radio in detection and ranging – what was often called the Radio Range Finder (RRF) – could be of value, particularly in any offensive role; offense not defense, totally dominated their thinking.
Imperial Army
In 1938, engineers from the Research Office of Nippon Electric Company (NECNEC
, a Japanese multinational IT company, has its headquarters in Minato, Tokyo, Japan. NEC, part of the Sumitomo Group, provides information technology and network solutions to business enterprises, communications services providers and government....
) were making coverage tests on high-frequency transmitters when rapid fading of the signal was observed. This occurred whenever an aircraft passed over the line between the transmitter and receiving meter. Masatsugu Kobayashi, the Manager of NEC’s Tube Department, recognized that this was due to the beat-frequency interference of the direct signal and the Doppler-shifted signal reflected from the aircraft.
Kobayashi suggested to the Army Science Research Institute that this phenomenon might be used as an aircraft warning method. Although the Army had rejected earlier proposals for using radio-detection techniques, this one had appeal because it was based on an easily understandable method and would require little developmental cost and risk to prove its military value. NEC assigned Kinji Satake of their Research Institute to develop a system called the Bi-static Doppler Interference Detector (BDID).
For testing the prototype system, it was set up on an area recently occupied by Japan along the coast of China. The system operated between 4.0-7.5 MHz (75–40 m) and involved a number of widely spaced stations; this formed a radio screen that could detect the presence (but nothing more) of an aircraft at distances up to 500 km (310.7 mi). The BDID was the Imperial Army’s first deployed radio-based detection system, placed into operation in early 1941.
A similar system was developed by Satake for the Japanese homeland. Information centers received oral warnings from the operators at BDID stations, usually spaced between 65 and 240 km (40 and 150 mi). To reduce homing vulnerability – a great fear of the military – the transmitters operated with only a few watts power. Although originally intended to be temporary until better systems were available, they remained in operation throughout the war. It was not until after the start of war the Imperial Army had equipment that could be called radar.
Imperial Navy
In the mid-1930s, some of the technical specialists in the Imperial Navy became interested in the possibility of using radio to detect aircraft. For consultation, they turned to Professor Yagi who, then the Director of the Radio Research Laboratory at Osaka Imperial University. Yagi suggested that this might be done by examining the Doppler frequency-shift in a reflected signal.Funding was provided to the Osaka Laboratory for experimental investigation of this technique. Kinjiro Okabe, the inventor of the split-anode magnetron and who had followed Yagi to Osaka, led the effort. Theoretical analyses indicated that the reflections would be greater if the wavelength was approximately the same as the size of aircraft structures. Thus, a VHF transmitter and receiver with Yagi antennas separated some distance were used for the experiment.
In 1936, Okabe successfully detected a passing aircraft by the Doppler-interference method; this was the first recorded demonstration in Japan of aircraft detection by radio. With this success, Okabe’s research interest switched from magnetrons to VHF equipment for target detection. This, however, did not lead to any significant funding. The top levels of the Imperial Navy believed that any advantage of using radio for this purpose were greatly outweighed by enemy intercept and disclosure of the sender’s presence.
Historically, warships in formation used lights and horns to avoid collision at night or when in fog. Newer techniques of VHF radio communications and direction-finding might also be used, but all of these methods were highly vulnerable to enemy interception. At the NTRI, Yoji Ito proposed that the UHF signal from a magnetron might be used to generate a very narrow beam that would have a greatly reduced chance of enemy detection.
Development of microwave system for collision avoidance started in 1939, when funding was provided by the Imperial Navy to JRC for preliminary experiments. In a cooperative effort involving Yoji Ito of the NTRI and Shigeru Nakajima of JRC, an apparatus using a 3-cm (10-GHz) magnetron with frequency modulation was designed and built. The equipment was used in an attempt to detect reflections from tall structures a few kilometers away. This experiment gave poor results, attributed to the very low power from the magnetron.
The initial magnetron was replaced by one operating at 16 cm (1.9 GHz) and with considerably higher power. The results were then much better, and in October 1940, the equipment obtained clear echoes from a ship in Tokyo Bay
Tokyo Bay
is a bay in the southern Kantō region of Japan. Its old name was .-Geography:Tokyo Bay is surrounded by the Bōsō Peninsula to the east and the Miura Peninsula to the west. In a narrow sense, Tokyo Bay is the area north of the straight line formed by the on the Miura Peninsula on one end and on...
at a distance of about 10 km (6.2 mi). There was still no commitment by top Japanese naval officials for using this technology aboard warships. Nothing more was done at this time, but late in 1941, the system was adopted for limited use.
In late 1940, Japan arranged for two technical missions to visit Germany and exchange information about their developments in military technology. Commander Yoji Ito represented the Navy’s interest in radio applications, and Lieutenant Colonel Kinji Satake did the same for the Army. During a visit of several months, they exchanged significant general information, as well as limited secret materials in some technologies, but little directly concerning radio-detection techniques. Neither side even mentioned magnetrons, but the Germans did apparently disclose their use of pulsed techniques.
After receiving the reports from the technical exchange in Germany, as well as intelligence reports concerning the success of Great Britain with firing using RDF, the Naval General Staff reversed itself and tentatively accepted pulse-transmission technology. On August 2, 1941, even before Yoji Ito returned to Japan, funds were allocated for the initial development of pulse-modulated radars. Commander Chuji Hashimoto of the NTRI was responsible for initiating this activity.
A prototype set operating at 4.2 m (71 MHz) and producing about 5 kW was completed on a crash basis. With the NTRI in the lead, the firm NEC and the Research Laboratory of Japan Broadcasting Corporation (NHK
NHK
NHK is Japan's national public broadcasting organization. NHK, which has always identified itself to its audiences by the English pronunciation of its initials, is a publicly owned corporation funded by viewers' payments of a television license fee....
) made major contributions to the effort. Kenjiro Takayanagi
Kenjiro Takayanagi
was a Japanese pioneer in the development of television. Although he failed to gain much recognition in the West, he built the world's first all-electronic television receiver, and is referred to as "the father of Japanese television".-Career:...
, Chief Engineer of NHK’s experimental television station and called “the father of Japanese television,” was especially helpful in rapidly developing the pulse-forming and timing circuits, as well as the receiver display. In early September 1941, the prototype set was first tested; it detected a single bomber at 97 km (60.3 mi) and a flight of aircraft at 145 km (90.1 mi).
The system, Japan’s first full Radio Range Finder (RRF – radar), was designated Mark 1 Model 1. Contracts were given to three firms for serial production; NEC built the transmitters and pulse modulators, Japan Victor the receivers and associated displays, and Fuji Electrical the antennas and their servo drives. The system operated at 3.0 m (100 MHz) with a peak-power of 40 kW. Dipole arrays with matte+-type reflectors were used in separate antennas for transmitting and receiving.
In November 1941, the first manufactured RRF was placed into service as a land-based early-warning system at Katsuura, Chiba
Katsuura, Chiba
is a city located in southern part of Chiba Prefecture, Japan. Katsuura city is famous for Katsuura Fishing Port, which features one of the top three largest morning markets in Japan. As of February 2010, the city has an estimated population of 20,570 and the density of 218 persons per km²...
, a town on the Pacific coast about 100 km (62.1 mi) from Tokyo. A large system, it weighed close to 8,700 kg (19,000 lb). The detection range was about 130 km (80.8 mi) for single aircraft and 250 km (155.3 mi) for groups.
Netherlands
Early radio-based detection in the NetherlandsNetherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
were along two independent lines: one a microwaves system at the firm Philips and the other a VHF system at a laboratory of the Armed Forces.
The Philips
Philips
Koninklijke Philips Electronics N.V. , more commonly known as Philips, is a multinational Dutch electronics company....
Company in Eindhoven, Netherlands
Netherlands
The Netherlands is a constituent country of the Kingdom of the Netherlands, located mainly in North-West Europe and with several islands in the Caribbean. Mainland Netherlands borders the North Sea to the north and west, Belgium to the south, and Germany to the east, and shares maritime borders...
, operated Natuurkundig Laboratorium (NatLab) for fundamental research related to its products. NatLab researcher Klass Posthumus developed a magnetron split into four elements.
In developing a communication system using this magnetron, C.H.J.A. Stall was testing the transmission by using parabolic
Parabolic reflector
A parabolic reflector is a reflective device used to collect or project energy such as light, sound, or radio waves. Its shape is that of a circular paraboloid, that is, the surface generated by a parabola revolving around its axis...
transmitting and receiving antennas set side-by-side, both aimed at a large plate some distance away. To overcome frequency instability of the magnetron, pulse modulation was used. It was found that the plate reflected a strong signal.
Recognizing the potential importance of this as a detection device, NatLab arranged a demonstration for the Koninklijke Marine (Royal Netherlands Navy
Royal Netherlands Navy
The Koninklijke Marine is the navy of the Netherlands. In the mid-17th century the Dutch Navy was the most powerful navy in the world and it played an active role in the wars of the Dutch Republic and later those of the Batavian Republic and the Kingdom of the Netherlands...
). This was conducted in 1937 across the entrance to the main naval port at Marsdiep
Marsdiep
The Marsdiep is a deep tide-race between Den Helder and Texel in the Netherlands, and running southwards between sandbanks. That gap connects the North Sea and the Waddenzee....
. Reflections from sea waves obscured the return from the target ship, but the Navy was sufficiently impressed to initiate sponsorship of the research. In 1939, an improved set was demonstrated at Wijk aan Zee, detecting a vessel at a distance of 3.2 km (2 mi).
A prototype system was built by Philips, and plans were started by the firm Nederlandse Seintoestellen Fabriek (a Philips subsidiary) for building a chain of warning stations to protect the primary ports. Some field testing of the prototype was conducted, but the project was discontinued when Germany invaded the Netherlands on May 10, 1940. Within the NatLab, however, the work was continued in great secrecy until 1942.
During the early 1930s, there were widespread rumours of a “death ray” being developed. The Dutch Parliament set up a Committee for the Applications of Physics in Weaponry under G.J. Elias to examine this potential, but the Committee quickly discounted death rays. The Committee did, however, establish the Laboratorium voor Fysieke Ontwikkeling (LFO, Laboratory for Physical Development), dedicated to supporting the Netherlands Armed Forces.
Operating in great secrecy, the LFO opened a facility called the Meetgebouw (Measurements Building) located on the Plain of Waalsdorp. In 1934, J.L.W.C. von Weiler joined the LFO and, with S.G. Gratama, began research on a 1.25-m (240-MHz) communication system to be used in artillery spotting.
In 1937, while tests were being conducted on this system, a passing flock of birds disturbed the signal. Realizing that this might be a potential method for detecting aircraft, the Minister of War ordered continuation of the experiments. Weiler and Gratama set about developing a system for directing searchlights and aiming anti-aircraft guns.
The experimental “electrical listening device” operated at 70 cm (430 MHz) and used pulsed transmission at an RPF of 10 kHz. A transmit-receive blocking circuit was developed to allow a common antenna. The received signal was displayed on a CR tube with a circular time base. This set was demonstrated to the Army in April 1938 and detected an aircraft at a range of 18 km (11.2 mi). The set was rejected, however, because it could not withstand the harsh environment of Army combat conditions.
The Navy was more receptive. Funding was provided for final development, and Max Staal was added to the team. To maintain secrecy, they divided the development into parts. The transmitter was built at the Delft Technical College
Delft University of Technology
Delft University of Technology , also known as TU Delft, is the largest and oldest Dutch public technical university, located in Delft, Netherlands...
and the receiver at the University of Leiden. Ten sets would be assembled under the personal supervision of J.J.A. Schagen van Leeuwen, head of the firm Hazemeijer Fabriek van Signaalapparaten.
The prototype had a peak-power of 1 kW, and used a pulse length of 2 to 3 μs with a 10- to 20 kHz PRF. The receiver was a super-heterodyne type using Acorn tubes and a 6 MHz IF stage. The antenna consisted of 4 rows of 16 half-wave dipoles backed by a 3- by 3-meter mesh screen. The operator used a bicycle-type drive to rotate the antenna, and the elevation could be changed using a hand crank.
Several sets were completed, and one was put into operation on the Malievelt in The Hague
The Hague
The Hague is the capital city of the province of South Holland in the Netherlands. With a population of 500,000 inhabitants , it is the third largest city of the Netherlands, after Amsterdam and Rotterdam...
just before the Netherlands fell to Germany in May 1940. The set worked well, spotting enemy aircraft during the first days of fighting. To prevent capture, operating units and plans for the system were destroyed. Von Weiler and Max Staal fled to England aboard one of the last ships able to leave, carrying two disassembled sets with them. Later, Gratama and van Leeuwen also escaped to England.
France
In 1927, French physicists Camille Gutton and Emile Pierret experimented with magnetrons and other devices generating wavelengths going down to 16 cm. Camille's son, Henri Gutton, was with the Compagnie Générale de Télégraphie Sans FilThomson-CSF
Thomson-CSF was a major electronics and defence contractor. In December 2000 it was renamed Thales Group.-History:In 1879 Elihu Thomson and Edwin Houston formed the Thomson-Houston Electric Company in the United States....
(CSF) where he and Robert Warneck improved his father's magnetrons.
Emile Girardeau
Emile Girardeau
Émile Girardeau was a French engineer, famous for being the first person to patent the original system of frequencies that is used today and known as the radar...
,the head of the CSF, recalled in testimony that they were at the time intending to build radio-detection systems "conceived according to the principles stated by Tesla.The " In 1934,following systematic studies on the magnetron the research of the CSF, headed by Maurice Ponte submitted a patent application for a device for detecting obstacles using continuous radiation of ultra-short wavelengths produced by a magnetron.These were still CW systems and depended on Doppler
Doppler
-Doppler effect and its applications:* Doppler effect* Doppler beaming* Doppler broadening* Doppler cooling** Doppler cooling limit* Doppler echocardiography** Doppler ultrasound, also called Doppler sonography** Transcranial doppler* Doppler fetal monitor...
interference for detection .However antennas were collocated The device was measuring distance and azimuth but not directly as in the later "radar" on a screen (1939), but it was the first patent of an operational radio-detection apparatus using centimetric wavelengths.
The system was tested in late 1934 aboard the cargo ship Oregon, with two transmitters working at 80 cm and 16 cm wavelengths. Coastlines and boats were detected from a range of 10-12 nautical miles. The shortest wavelength was chosen for the final design, which equipped the liner SS Normandie
SS Normandie
SS Normandie was an ocean liner built in Saint-Nazaire, France for the French Line Compagnie Générale Transatlantique. She entered service in 1935 as the largest and fastest passenger ship afloat; she is still the most powerful steam turbo-electric-propelled passenger ship ever built.Her novel...
as early as mid-1935 for operational use.
In late 1937, Maurice Elie at SFR developed a means of pulse-modulating transmitter tubes. This led to a new 16-cm system with a peak power near 500 W and a pulse width of 6 μs. . French and U.S. patents were filed in December 1939. The system was planned to be sea-tested aboard the Normandie, but this was cancelled at the outbreak of war.
Pierre David at the Laboratori National de Radioelectricite (National Laboratory of Radioelectricity, LNR) experimented with reflected radio signals at about a meter wavelength. Starting in 1931, he observed that aircraft caused interference to the signals. The LNR then initiated research on a detection technique called barrage électromagnétique (electromagnetic curtain). While this could indicate the general location of penetration, precise determination of direction and speed was not possible.
In 1936, the Défense Aérienne de Territoire (Defence of Air Territory), ran tests on David’s electromagnetic curtain. In the tests, the system detected most of the entering aircraft, but too many were missed. As the war grew closer, the need for an aircraft detection was critical. David realized the advantages of a pulsed system, and in October 1938 he designed a 50 MHz, pulse-modulated system with a peak-pulse power of 12 kW. This was built by the firm SADIR.
France declared war on Germany on September 1, 1939, and there was a great need for an early-warning detection system. The SADIR system was taken to near Toulon
Toulon
Toulon is a town in southern France and a large military harbor on the Mediterranean coast, with a major French naval base. Located in the Provence-Alpes-Côte-d'Azur region, Toulon is the capital of the Var department in the former province of Provence....
, and detected and measured the range of invading aircraft as far as 55 km (34.2 mi). The SFR pulsed system was set up near Paris where it detected aircraft at ranges up to 130 km (80.8 mi). To further improve the SFR system, Henri Gutton and Warnecke developed a 500-cm (600-MHz) magnetron with an oxide-coated cathode that produced 500 W. In May 1940, just before the Germans arrived, several of the new magnetrons were taken to Great Britain where their oxide-coated cathods were incorporated to improve the Boots and Randall magnetron.
Italy
Guglielmo MarconiGuglielmo Marconi
Guglielmo Marconi was an Italian inventor, known as the father of long distance radio transmission and for his development of Marconi's law and a radio telegraph system. Marconi is often credited as the inventor of radio, and indeed he shared the 1909 Nobel Prize in Physics with Karl Ferdinand...
initiated the research in Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
on radio-based detection technology. In 1933, while participating with his Italian firm in experiments with a 600 MHz communications link across Rome
Rome
Rome is the capital of Italy and the country's largest and most populated city and comune, with over 2.7 million residents in . The city is located in the central-western portion of the Italian Peninsula, on the Tiber River within the Lazio region of Italy.Rome's history spans two and a half...
, he noted transmission disturbances caused by moving objects adjacent to its path. This led to the development at his laboratory at Cornegliano of a 330-MHz (0.91-m) CW Doppler detection system that he called radioecometro. Barkhausen-Kurz tube
Barkhausen-Kurz tube
The Barkhausen-Kurz tube, also called the B-K oscillator, was commonly used in early electronic systems operating in the ultra-high frequency portion of the radio spectrum.-Development:...
s were used in both the transmitter and receiver.
In May 1935, Marconi demonstrated his system to the Fascist dictator Benito Mussolini
Benito Mussolini
Benito Amilcare Andrea Mussolini was an Italian politician who led the National Fascist Party and is credited with being one of the key figures in the creation of Fascism....
and members of the military General Staff; however the output power was insufficient for military use. While Marconi’s demonstration raised considerable interest, little more was done with his apparatus.
Mussolini directed that radio-based detection technology be further developed, and it was assigned to the Regio Instituto Electrotecnico e delle Comunicazioni (RIEC, Royal Institute for Electro-technics and Communications). The RIEC had been established in 1916 on the campus of the Italian Naval Academy
Accademia Navale di Livorno
The Italian Naval Academy is a coeducational military university in Leghorn , which is responsible for the technical training of military officers of the Italian Navy.-The Hospital of St. James:...
in Livorno
Livorno
Livorno , traditionally Leghorn , is a port city on the Tyrrhenian Sea on the western edge of Tuscany, Italy. It is the capital of the Province of Livorno, having a population of approximately 160,000 residents in 2009.- History :...
. Lieutenant Ugo Tiberio, a physics and radio-technology instructor at the Academy, was assigned to head the project on a part-time basis.
Tiberio prepared a report on developing an experimental apparatus that he called telemetro radiofonico del rivelatore (RDT, Radio-Detector Telemetry). The report, submitted in mid-1936, included what was later known as the radar range equation. When the work got underway, Nello Carrara, a civilian physics instructor who had been doing research at the RIEC in microwaves, was added to be responsible for developing the RDT transmitter.
Before the end of 1936, Tiberio and Carrara had demonstrated the EC-1, the first Italian RDT system. This had an FM
Frequency modulation
In telecommunications and signal processing, frequency modulation conveys information over a carrier wave by varying its instantaneous frequency. This contrasts with amplitude modulation, in which the amplitude of the carrier is varied while its frequency remains constant...
transmitter operating at 200 MHz (1.5 m) with a single parabolic
Parabolic antenna
A parabolic antenna is an antenna that uses a parabolic reflector, a curved surface with the cross-sectional shape of a parabola, to direct the radio waves. The most common form is shaped like a dish and is popularly called a dish antenna or parabolic dish...
cylinder antenna. It detected by mixing the transmitted and the Doppler-shifted reflected signals, resulting in an audible tone.
The EC-1 did not provide a range measurement; to add this capability, development of a pulsed system was initiated in 1937. Captain Alfeo Brandimarte joined the group and primarily designed the first pulsed system, the EC-2. This operated at 175 MHz (1.7 m) and used a single antenna made with a number of equi-phased dipoles. The detected signal was intended to be displayed on an oscilloscope. There were many problems, and the system never reached the testing stage.
Work then turned to developing higher power and operating frequencies. Carrara, in cooperation with the firm FIVRE, developed a magnetron-like device. This was composed of a pair of triodes connected to a resonate cavity and produced 10 kW at 425 MHz (70 cm). It was used in designing two versions of the EC-3, one for shipboard and the other for coastal defense.
Italy, joining Germany, entered WWII in September 1939 without an operational RDT. A breadboard of the EC-3 was built and tested from atop a building at the Academy, but most RDT work was stopped as direct support of the war took priority.
Other Nations
In early 1939, the British Government invited representatives from the most technically advanced Commonwealth Nations to visit England for briefings and demonstrations on the highly secret RDF (radar) technology. Based on this, RDF developments were started in AustraliaAustralia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, and South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
by September 1939. In addition, this technology was independently developed in Hungary
Hungary
Hungary , officially the Republic of Hungary , is a landlocked country in Central Europe. It is situated in the Carpathian Basin and is bordered by Slovakia to the north, Ukraine and Romania to the east, Serbia and Croatia to the south, Slovenia to the southwest and Austria to the west. The...
early in the war period.
In Australia, the Radiophysics Laboratory was established at Sydney University under the Council for Scientific and Industrial Research; John H. Piddington was responsible for RDF development. The first project was a 200-MHz (1.5-m) shore-defense system for the Australian Army
Australian Army
The Australian Army is Australia's military land force. It is part of the Australian Defence Force along with the Royal Australian Navy and the Royal Australian Air Force. While the Chief of Defence commands the Australian Defence Force , the Army is commanded by the Chief of Army...
. Designated ShD, this was first tested in September 1941, and eventually installed at 17 ports. Following the Japanese attack on Pearl Harbor
Attack on Pearl Harbor
The attack on Pearl Harbor was a surprise military strike conducted by the Imperial Japanese Navy against the United States naval base at Pearl Harbor, Hawaii, on the morning of December 7, 1941...
, the Royal Australian Air Force
Royal Australian Air Force
The Royal Australian Air Force is the air force branch of the Australian Defence Force. The RAAF was formed in March 1921. It continues the traditions of the Australian Flying Corps , which was formed on 22 October 1912. The RAAF has taken part in many of the 20th century's major conflicts...
urgently needed an air-warning system, and Piddington’s team, using the ShD as a basis, put the AW Mark I together in five days. It was being installed in Darwin, Northern Territory
Darwin, Northern Territory
Darwin is the capital city of the Northern Territory, Australia. Situated on the Timor Sea, Darwin has a population of 127,500, making it by far the largest and most populated city in the sparsely populated Northern Territory, but the least populous of all Australia's capital cities...
, when Australia received the first Japanese attack on February 19, 1942. A short time later, it was converted to a light-weight transportable version, the LW-AW Mark II; this was used by the Australian forces, as well as the U.S. Army, in early island landings in the South Pacific.
The early RDF developments in Canada were at the Radio Section of the National Research Council of Canada
National Research Council of Canada
The National Research Council is an agency of the Government of Canada which conducts scientific research and development.- History :...
. Using commercial components and with essentially no further assistance from Great Britain, John Tasker Henderson led a team in developing the Night Watchman, a surface-warning system for the Royal Canadian Navy
Royal Canadian Navy
The history of the Royal Canadian Navy goes back to 1910, when the naval force was created as the Naval Service of Canada and renamed a year later by King George V. The Royal Canadian Navy is one of the three environmental commands of the Canadian Forces...
to protect the entrance to the Halifax Harbour
Halifax Harbour
Halifax Harbour is a large natural harbour on the Atlantic coast of Nova Scotia, Canada, located in the Halifax Regional Municipality.-Harbour description:The harbour is called Jipugtug by the Mi'kmaq first nation, anglisized as Chebucto...
. Successfully tested in July 1940, this set operated at 200 MHz (1.5 m), had a 1 kW output with a pulse length of 0.5 μs, and used a relatively small, fixed antenna. This was followed by a ship-borne set designated Surface Warning 1st Canadian (SW1C) with the antenna hand-rotated; this was first tested at sea in mid-May 1941, For coastal defense by the Canadian Army
Canadian Forces Land Force Command
The Canadian Army , previously called Land Force Command, is responsible for army operations within the Canadian Forces. The current size of the Army is 19,500 regular soldiers and 16,000 reserve soldiers, for a total of around 35,500 soldiers...
, a 200 MHz set with a transmitter similar to the Night Watchman was developed. Designated CD, it used a large, rotating antenna atop a 70 feet (21.3 m) wooden tower. The CD was put into operation in January 1942.
Ernest Marsden
Ernest Marsden
Sir Ernest Marsden was an English-New Zealand physicist. He was born in East Lancashire, living in Rishton and educated at Queen Elizabeth's Grammar School, Blackburn, where an inter-house trophy rewarding academic excellence bears his name.He met Ernest Rutherford at the University of Manchester...
represented New Zealand at the briefings in England, and then established two facilities for RDF development – one in Wellington
Wellington
Wellington is the capital city and third most populous urban area of New Zealand, although it is likely to have surpassed Christchurch due to the exodus following the Canterbury Earthquake. It is at the southwestern tip of the North Island, between Cook Strait and the Rimutaka Range...
at the Radio Section of the Central NZ Post Office, and another at Canterbury University College in Christchurch
Christchurch
Christchurch is the largest city in the South Island of New Zealand, and the country's second-largest urban area after Auckland. It lies one third of the way down the South Island's east coast, just north of Banks Peninsula which itself, since 2006, lies within the formal limits of...
. Charles N. Watson-Munro led the development of land-based and airborne sets at Wellington, while Frederick W. G. White led the development of shipboard sets at Christchurch.
Before the end of 1939, the Wellington group had converted an existing 180-MHz (1.6-m), 1 kW transmitter to produce 2-μs pulses and tested it to detect large vessels at up to 30 km; this was designated CW (Coastal Watching). A similar set, designated CD (Coast Defense) used a CRT for display and had lobe-switching on the receiving antenna; this was deployed in Wellington in late 1940. A partially completed ASV 200 MHz set was brought from Great Britain by Marsden, and another group at Wellington built this into an aircraft set for the Royal New Zealand Air Force
Royal New Zealand Air Force
The Royal New Zealand Air Force is the air arm of the New Zealand Defence Force...
; this was first flown in early 1940. At Christchurch, there was a smaller staff and work went slower, but by July 1940, a 430-MHz (70-cm), 5 kW set was tested. Two types, designated SW (Ship Warning) and SWG (Ship Warning, Gunnery), were placed into service by the Royal New Zealand Navy
Royal New Zealand Navy
The Royal New Zealand Navy is the maritime arm of the New Zealand Defence Force...
starting in August 1941. In all some 44 types were developed in New Zealand during WW11.
South Africa did not have a representative at the 1939 meetings in England, but in mid-September, as Ernest Marsden was returning by ship to New Zealand, Basil F. J. Schonland
Basil Schonland
Sir Basil Ferdinand Jamieson Schonland CBE FRS was the first president of the South African Council for Scientific and Industrial Research.-Birth and Parentage:...
came aboard and received three days of briefings. Schonland, a world authority on lightning and Director of the Bernard Price Institute of Geophysics at Witwatersrand University, immediately started an RDF development using amateur radio components and Institute’s lightning-monitoring equipment. Designated JB (for Johannesburg
Johannesburg
Johannesburg also known as Jozi, Jo'burg or Egoli, is the largest city in South Africa, by population. Johannesburg is the provincial capital of Gauteng, the wealthiest province in South Africa, having the largest economy of any metropolitan region in Sub-Saharan Africa...
), the 90-MHz (3.3-m), 500-W mobile system was tested in November 1939, just two months after its start. The prototype was operated in Durban
Durban
Durban is the largest city in the South African province of KwaZulu-Natal and the third largest city in South Africa. It forms part of the eThekwini metropolitan municipality. Durban is famous for being the busiest port in South Africa. It is also seen as one of the major centres of tourism...
before the end of 1939, detecting ships and aircraft at distances up to 80 km, and by the next March a system was fielded by anti-aircraft brigades of the South African Defence Force
South African Defence Force
The South African Defence Force was the South African armed forces from 1957 until 1994. The former Union Defence Force was renamed to the South African Defence Force in the Defence Act of 1957...
.
In Hungary, Zoltán Lajos Bay
Zoltán Lajos Bay
Zoltán Lajos Bay was a Hungarian physicist, professor, and engineer who developed microwave technology, including tungsten lamps. He was the first person to observe radar echoes from the Moon...
was a Professor of Physics at the Technical University of Budapest as well as the Research Director of Egyesült Izzolampa (IZZO), a radio and electrical manufacturing firm. In late 1942, IZZO was directed by the Minister of Defense to develop a radio-location (rádiólokáció, radar) system. Using journal papers on ionospheric measurements for information on pulsed transmission, Bay developed a system called Sas (Eagle) around existing communications hardware.
The Sas operated at 120 MHz (2.5 m) and was in a cabin with separate transmitting and receiving dipole arrays attached; the assembly was all on a rotatable platform. According to published records, the system was tested in 1944 atop Mount János and had a range of “better than 500 km.” A second Sas was installed at another location. There is no indication that either Sas installation was ever in regular service. After the war, Bay used a modified Sas to successfully bounce a signal off the moon.
World War II Radar
At the start of World War IIWorld War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...
in September 1939, both the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...
and Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...
knew of each other's ongoing efforts in radio navigation
Radio navigation
Radio navigation or radionavigation is the application of radio frequencies to determine a position on the Earth. Like radiolocation, it is a type of radiodetermination.The basic principles are measurements from/to electric beacons, especially...
and its countermeasures – the "Battle of the beams
Battle of the beams
The Battle of the Beams was a period early in the Second World War when bombers of the German Air Force used a number of increasingly accurate systems of radio navigation for night bombing. British "scientific intelligence" at the Air Ministry fought back with a variety of increasingly effective...
". Also, both nations were generally aware of, and intensely interested in, the other's developments in radio-based detection and tracking, and engaged in an active campaign of espionage
Espionage
Espionage or spying involves an individual obtaining information that is considered secret or confidential without the permission of the holder of the information. Espionage is inherently clandestine, lest the legitimate holder of the information change plans or take other countermeasures once it...
and false leaks about their respective equipment. By the time of the Battle of Britain
Battle of Britain
The Battle of Britain is the name given to the World War II air campaign waged by the German Air Force against the United Kingdom during the summer and autumn of 1940...
, both sides were deploying range and direction-finding units (radars) and control stations as part of integrated air defense capability. However, the German Funkmessgerät (radio measuring device) systems could not assist in an offensive role and was thus not supported by Adolf Hitler
Adolf Hitler
Adolf Hitler was an Austrian-born German politician and the leader of the National Socialist German Workers Party , commonly referred to as the Nazi Party). He was Chancellor of Germany from 1933 to 1945, and head of state from 1934 to 1945...
. Also, the Luftwaffe
Luftwaffe
Luftwaffe is a generic German term for an air force. It is also the official name for two of the four historic German air forces, the Wehrmacht air arm founded in 1935 and disbanded in 1946; and the current Bundeswehr air arm founded in 1956....
did not sufficiently appreciate the importance of British Range and Direction Finding
Range and Direction Finding
Range and Direction Finding was the initial technique and hardware in Great Britain that eventually came to be called 'radar.'Since the earliest days of radio , the signals had been used in direction finding on land, sea, and in the air...
(RDF) stations as part of RAF
Royal Air Force
The Royal Air Force is the aerial warfare service branch of the British Armed Forces. Formed on 1 April 1918, it is the oldest independent air force in the world...
's air defense capability, contributing to their failure.
While the United Kingdom and Germany led in pre-war advances in the use of radio for detection and tracking of aircraft, there were also developments in the United States, the Soviet Union, and Japan. Wartime systems in all of these nations will be summarized. The acronym RADAR (for RAdio Detection And Ranging) was coined by the U.S. Navy in 1940, and the subsequent name "radar" was soon widely used.
Post-WWII Radar
World War II, which gave impetus to the great surge in radar development, ended between the Allies and Germany in May 1945, followed by Japan in August. With this, radar activities in Germany and Japan ceased for a number of years. In other countries, particularly the United States, Great Britain, and the USSR, the politically unstable post-war years saw continued radar improvements for military applications. In fact, these three nations all made significant efforts in bringing scientists and engineers from Germany to work in their weapon programs; in the U.S., this was under Operation PaperclipOperation Paperclip
Operation Paperclip was the Office of Strategic Services program used to recruit the scientists of Nazi Germany for employment by the United States in the aftermath of World War II...
.
Even before the end of the war, various project directed toward non-military applications of radar and closely related technologies were initiated. The US Army Air Forces and the British RAF had made wartime advances in using radar for handling aircraft landing, and this was rapidly expanded into the civil sector. The field of radio astronomy
Radio astronomy
Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The initial detection of radio waves from an astronomical object was made in the 1930s, when Karl Jansky observed radiation coming from the Milky Way. Subsequent observations have identified a number of...
was one of the related technologies; although discovered before the war, it immediately flourished in the late 1940s with many scientists around the world establishing new careers based on their radar experience.
Four techniques, highly important in post-war radars, were matured in the late 1940s-early 1950s: pulse Doppler, monopulse, phased array, and synthetic aperture; the first three were known and even used during wartime developments, but were matured later.
- Pulse-Doppler radarPulse-doppler radarPulse-Doppler is a 4D radar system capable of detecting both target 3D location as well as measuring radial velocity . It uses the Doppler effect to avoid overloading computers and operators as well as to reduce power consumption...
(often known as moving target indication or MTI), uses the Doppler-shifted signals from targets to better detect moving targets in the presence of clutter. - Monopulse radarMonopulse radarMonopulse radar is an adaptation of conical scanning radar which sends additional information in the radar signal in order to avoid problems caused by rapid changes in signal strength. The system also makes jamming more difficult...
(also called simultaneous lobing) was conceived by Robert PageRobert Morris PageRobert Morris Page was an American physicist who was a leading figure in the development of radar technology. Later, Page served as the Director of Research for the U.S. Naval Research Laboratory.-Life and career:...
at the NRL in 1943. With this, the system derives error-angle information from a single pulse, greatly improving the tracking accuracy. - Phased-array radarPhased arrayIn wave theory, a phased array is an array of antennas in which the relative phases of the respective signals feeding the antennas are varied in such a way that the effective radiation pattern of the array is reinforced in a desired direction and suppressed in undesired directions.An antenna array...
has the many segments of a large antenna separately controlled, allowing the beam to be quickly directed. This greatly reduces the time necessary to change the beam direction from one point to another, allowing almost simultaneous tracking of multiple targets while maintaining overall surveillance. - Synthetic-aperture radar (SAR), was invented in the early 1950s at Goodyear Aircraft Corporation. Using a single, relatively small antenna carried on an aircraft, a SAR combines the returns from each pulse to produce a high-resolution image of the terrain comparable that that obtained by a much larger antenna. SAR has wide applications, particularly in mapping and remote sensingRemote sensingRemote sensing is the acquisition of information about an object or phenomenon, without making physical contact with the object. In modern usage, the term generally refers to the use of aerial sensor technologies to detect and classify objects on Earth by means of propagated signals Remote sensing...
.
One of the early applications of digital computers
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
was in switching the signal phase in elements of large phased-array antennas. As smaller computers came into being, these were quickly applied to digital signal processing
Digital signal processing
Digital signal processing is concerned with the representation of discrete time signals by a sequence of numbers or symbols and the processing of these signals. Digital signal processing and analog signal processing are subfields of signal processing...
using algorithms for improve radar performance.
Other advances in radar systems and applications in the decades following WWII are far too many to be included herein. The following sections are intended to provide representative samples.
Military Radars
In the United States, the Rad Lab at MIT officially closed at the end of 1945. The Naval Research Laboratory (NRL) and the Army’s Evans Signal Laboratory continued with new activities in centimeter radar development. The United States Air ForceUnited States Air Force
The United States Air Force is the aerial warfare service branch of the United States Armed Forces and one of the American uniformed services. Initially part of the United States Army, the USAF was formed as a separate branch of the military on September 18, 1947 under the National Security Act of...
(USAF) – separated from the Army in 1946 – concentrated radar research at their Cambridge Research Center (CRC) at Hanscom Field
Hanscom Air Force Base
Hanscom Air Force Base is a United States Air Force base located approximately south-southwest of Bedford, Massachusetts. The facility is a joint use civil airport/military base with Hanscom Field which provides general aviation and charter service.The host unit at Hanscom is the non-flying...
, Massachusetts. In 1951, MIT opened the Lincoln Laboratory
Lincoln Laboratory
MIT Lincoln Laboratory, located in Lexington, Massachusetts, is a United States Department of Defense research and development center chartered to apply advanced technology to problems of national security. Research and development activities focus on long-term technology development as well as...
for joint developments with the CRC. While the Bell Telephone Laboratories embarked on major communications upgrades, they continued with the Army in radar for their ongoing Nike air-defense program
In Great Britain, the RAF’s Telecommunications Research Establishment
Telecommunications Research Establishment
The Telecommunications Research Establishment was the main United Kingdom research and development organization for radio navigation, radar, infra-red detection for heat seeking missiles, and related work for the Royal Air Force during World War II and the years that followed. The name was...
(TRE) and the Army’s Radar Research and Development Establishment
Signals Research and Development Establishment
The Signals Research and Development Establishment was a British government military research establishment, based in Christchurch, Dorset from 1948 until it merged with the Royal Radar Establishment in Malvern, Worcestershire to form the Royal Signals and Radar Establishment in 1980...
(RRDE) both continued at reduced levels at Malvern, Worcestershire
Malvern, Worcestershire
Malvern is a town and civil parish in Worcestershire, England, governed by Malvern Town Council. As of the 2001 census it has a population of 28,749, and includes the historical settlement and commercial centre of Great Malvern on the steep eastern flank of the Malvern Hills, and the former...
, then in 1953 were combined to form the Radar Research Establishment. In 1948, all of the Royal Navy’s radio and radar R&D activities were combined to form the Admiralty Signal and Radar Establishment
HMS Mercury (shore establishment)
HMS Mercury was a shore establishment of the Royal Navy, and the site of the Royal Navy Signals School and Combined Signals School. There was also a subsidiary branch, HMS Mercury II.-Establishment and history:...
, located near Portsmouth
Portsmouth
Portsmouth is the second largest city in the ceremonial county of Hampshire on the south coast of England. Portsmouth is notable for being the United Kingdom's only island city; it is located mainly on Portsea Island...
, Hampshire
Hampshire
Hampshire is a county on the southern coast of England in the United Kingdom. The county town of Hampshire is Winchester, a historic cathedral city that was once the capital of England. Hampshire is notable for housing the original birthplaces of the Royal Navy, British Army, and Royal Air Force...
. The USSR, although devastated by the war, immediately embarked on the development of new weapons, including radars.
During the Cold War
Cold War
The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...
period following WWII, the primary "axis" of combat shifted to lie between the United States and the Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....
. By 1949, both sides had nuclear weapons carried by bombers. To provide early warning of an attack, both deployed huge radar networks of increasing sophistication at ever-more remote locations. In the West, the first such system was the Pinetree Line
Pinetree Line
The Pinetree Line was a series of radar stations located across the northern United States and southern Canada at about the 50th parallel north, along with a number of other stations located on the Atlantic and Pacific coasts. Run by NORAD , over half were manned by United States Air Force...
, deployed across Canada in the early 1950s, backed up with radar picket
Radar picket
A radar picket is a radar-equipped ship, submarine, aircraft, or vehicle used to increase the radar detection range around a force to protect it from surprise attack. Often several detached radar units encircle a force to provide increased cover in all directions.-World War II:Radar picket ships...
s on ships and oil platforms off the east and west coasts.
The Pinetree Line initially used vintage pulsed radars and was soon supplemented with the Mid-Canada Line
Mid-Canada Line
The Mid-Canada Line, also known as the McGill Fence, was a line of radar stations across the "middle" of Canada to provide early warning of a Soviet bomber attack on North America. It was built to supplement the less-advanced Pinetree Line, which was located further south...
(MCL). Soviet technology improvements made these Lines inadequate and, in a construction project involving 25,000 persons, the Distant Early Warning Line
Distant Early Warning Line
The Distant Early Warning Line, also known as the DEW Line or Early Warning Line, was a system of radar stations in the far northern Arctic region of Canada, with additional stations along the North Coast and Aleutian Islands of Alaska, in addition to the Faroe Islands, Greenland, and Iceland...
(DEW Line) was completed in 1957. Stretching from Alaska
Alaska
Alaska is the largest state in the United States by area. It is situated in the northwest extremity of the North American continent, with Canada to the east, the Arctic Ocean to the north, and the Pacific Ocean to the west and south, with Russia further west across the Bering Strait...
to Baffin Island
Baffin Island
Baffin Island in the Canadian territory of Nunavut is the largest island in the Canadian Arctic Archipelago, the largest island in Canada and the fifth largest island in the world. Its area is and its population is about 11,000...
and covering over 6000 miles (9,656 km), the DEW Line consisted of 63 stations with AN/FPS-19 high-power, pulsed, L-Band radars, most augmented by AN/FPS-23 pulse-Doppler systems. The Soviet Unit tested its first Intercontinental Ballistic Missile
Intercontinental ballistic missile
An intercontinental ballistic missile is a ballistic missile with a long range typically designed for nuclear weapons delivery...
(ICBM) in August 1957, and in a few years the early-warning role was passed almost entirely to the more capable DEW Line.
Both the U.S. and the Soviet Union then had ICBMs with nuclear warheads, and each began the development of a major anti-ballistic missile (ABM) system. In the USSR, this was the Fakel V-1000, and for this they developed powerful radar systems. This was eventually deployed around Moscow as the A-35 anti-ballistic missile system
A-35 anti-ballistic missile system
The A-35 anti-ballistic missile system, or A-35 Aldan, was a Soviet military battle management radar complex deployed around Moscow to intercept enemy missiles targeting the city or its surrounding areas. In development since the 1960s and in operation from 1971 until the 1990s, It featured the...
, supported by radars designated by NATO as the Cat House
Cat House radar
The Cat House Soviet radar system was part of the Soviet radar system originally based in the former Soviet Union, what is today Russia. The 'Cat House' system is a long range early detection radar built to detect American ballistic missiles fired at Moscow.-System:Cat House was one part of a...
, Dog House, and Hen House.
In 1957, the U.S. Army initiated an ABM system first called Nike-X; this passed through several names, eventually becoming the Safeguard Program
Safeguard Program
The Safeguard Program was a United States Army anti-ballistic missile system developed during the late 1960s. Safeguard was designed to protect U.S. ICBM missile sites from counterforce attack, thus preserving the option of an unimpeded retaliatory strike. Safeguard used much of the same technology...
. For this, there was a long-range Perimeter Acquisition Radar (PAR) and a shorter-range, more precise Missile Site Radar (MSR).
The PAR was housed in a 128 feet (39 m)-high nuclear-hardened building with one face sloping 25 degrees facing north. This contained 6,888 antenna elements separated in transmitting and receiving phased arrays. The L-Band transmitter used 128 long-life traveling-wave tubes (TWTs), having a combined power in the megawatt range The PAR could detect incoming missiles outside the atmosphere at distances up to 1800 miles (2,896.8 km).
The MSR had an 80 feet (24.4 m), truncated pyramid structure, with each face holding a phased-array antenna 13 feet (4 m) in diameter and containing 5,001 array elements used for both transmitting and receiving. Operating in the S-Band, the transmitter used two klystron
Klystron
A klystron is a specialized linear-beam vacuum tube . Klystrons are used as amplifiers at microwave and radio frequencies to produce both low-power reference signals for superheterodyne radar receivers and to produce high-power carrier waves for communications and the driving force for modern...
s functioning in parallel, each with megawatt-level power. The MSR could search for targets from all directions, acquiring them at up to 300 miles (482.8 km) range.
One Safeguard site, intended to defend Minuteman ICBM
LGM-30 Minuteman
The LGM-30 Minuteman is a U.S. nuclear missile, a land-based intercontinental ballistic missile . As of 2010, the version LGM-30G Minuteman-III is the only land-based ICBM in service in the United States...
missile silos near the Grand Forks AFB in North Dakota
North Dakota
North Dakota is a state located in the Midwestern region of the United States of America, along the Canadian border. The state is bordered by Canada to the north, Minnesota to the east, South Dakota to the south and Montana to the west. North Dakota is the 19th-largest state by area in the U.S....
, was finally completed in October 1975, but the U.S. Congress withdrew all funding after it was operational but a single day. During the following decades, the U.S. Army and the U.S. Air Force developed a variety of large radar systems, but the long-serving BTL gave up military development work in the 1970s.
A modern radar developed by of the U.S. Navy that should be noted is the AN/SPY-1
AN/SPY-1
The AN/SPY-1 is a US naval radar system manufactured by Lockheed Martin. The array is a passive electronically scanned system and is a key component of the Aegis Combat System. The system is computer controlled, using four complementary antennas to provide 360 degree coverage...
. First fielded in 1973, this S-Band, 6 MW system has gone through a number of variants and is a major component of the Aegis Combat System
Aegis combat system
The Aegis Combat System is an integrated naval weapons system developed by the Missile and Surface Radar Division of RCA, and now produced by Lockheed Martin...
. An automatic detect-and-track system, it is computer controlled using four complementary three-dimensional passive electronically scanned array
Passive electronically scanned array
A passive electronically scanned array , contrary to its active counterpart AESA, is a phased array which has a central radiofrequency source , sending energy into phase shift modules, which then send energy into the various emitting elements in the front of the antenna...
antennas to provide hemispherical coverage.
Radar signals, traveling with line-of-sight propagation
Line-of-sight propagation
Line-of-sight propagation refers to electro-magnetic radiation or acoustic wave propagation. Electromagnetic transmission includes light emissions traveling in a straight line...
, normally have a range to ground targets limited by the visible horizon
Horizon
The horizon is the apparent line that separates earth from sky, the line that divides all visible directions into two categories: those that intersect the Earth's surface, and those that do not. At many locations, the true horizon is obscured by trees, buildings, mountains, etc., and the resulting...
, or less than about 10 miles (16.1 km). Airborne targets can be detected by ground-level radars at greater ranges, but, at best, several hundred miles. Since the beginning of radio, it had been known that signals of appropriate frequencies (3 to 30 MHz) could be “bounced” from the ionosphere
Ionosphere
The ionosphere is a part of the upper atmosphere, comprising portions of the mesosphere, thermosphere and exosphere, distinguished because it is ionized by solar radiation. It plays an important part in atmospheric electricity and forms the inner edge of the magnetosphere...
and received at considerable distances. As long-range bombers and missiles came into being, there was a need to have radars give early warnings at great ranges. In the early 1950s, a team at the Naval Research Laboratory came up with the Over-the-Horizon (OTH) radar
Over-the-horizon radar
Over-the-horizon radar, or OTH , is a design concept for radar systems to allow them to detect targets at very long ranges, typically up to thousands of kilometers...
for this purpose.
To distinguish targets from other reflections, it was necessary to use a phase-Doppler system. Very sensitive receivers with low-noise amplifier
Low-noise amplifier
Low-noise amplifier is an electronic amplifier used to amplify possibly very weak signals . It is usually located very close to the detection device to reduce losses in the feedline. This active antenna arrangement is frequently used in microwave systems like GPS, because coaxial cable feedline is...
s had to be developed. Since the signal going to the target and returning had a propagation loss proportional to the range raised to the fourth power, a powerful transmitter and large antennas were required. A digital computer with considerable capability (new at that time) was necessary for analyzing the data. In 1950, their first experimental system was able to detect rocket launches 600 miles (965.6 km) away at Cape Canaveral, and the cloud from a nuclear explosion in Nevada 1700 miles (2,735.9 km) distant.
In the early 1970s, a joint American-British project, code named Cobra Mist
Cobra Mist
Cobra Mist was the codename for an Anglo-American experimental over-the-horizon radar station at Orford Ness, Suffolk, England . It was known technically as AN/FPS-95 and sometimes referred to as System 441a; a reference to the project as a whole. Cobra Mist was part of a small number of "Cobra"...
, used a 10-MW OTH radar at Orfordness (the birthplace of British radar), England, in an attempt to detect aircraft and missile launchings over the Western USSR. Because of US-USSR ABM agreements, this was abandoned within two years. In the same time period, the Soviets were developing a similar system; this successfully detected a missile launch at 2500 km (1,553.4 mi). By 1976, this had matured into an operational system named Duga (“Arc” in English), but known to western intelligence as Steel Yard and called Woodpecker
Russian Woodpecker
The Russian Woodpecker was a notorious Soviet signal that could be heard on the shortwave radio bands worldwide between July 1976 and December 1989. It sounded like a sharp, repetitive tapping noise, at 10 Hz, giving rise to the "Woodpecker" name...
by radio amateurs and others who suffered from its interference – the transmitter was estimated to have a power of 10 MW. Australia, Canada, and France also developed OTH radar systems.
With the advent of satellite
Satellite
In the context of spaceflight, a satellite is an object which has been placed into orbit by human endeavour. Such objects are sometimes called artificial satellites to distinguish them from natural satellites such as the Moon....
s with early-warning capabilities, the military lost most of its interest in OTH radars. However, in recent years, this technology has been reactivated for detecting and tracking ocean shipping in applications such as maritime reconnaissance and drug enforcement.
Systems using an alternate technology have also been developed for over-the-horizon detection. Due to diffraction
Diffraction
Diffraction refers to various phenomena which occur when a wave encounters an obstacle. Italian scientist Francesco Maria Grimaldi coined the word "diffraction" and was the first to record accurate observations of the phenomenon in 1665...
, electromagnetic surface wave
Surface wave
In physics, a surface wave is a mechanical wave that propagates along the interface between differing media, usually two fluids with different densities. A surface wave can also be an electromagnetic wave guided by a refractive index gradient...
s are scattered to the rear of objects, and these signals can be detected in a direction opposite from high-powered transmissions. Called OTH-SW (SW for Surface Wave), Russia is using such a system to monitor the Sea of Japan
Sea of Japan
The Sea of Japan is a marginal sea of the western Pacific Ocean, between the Asian mainland, the Japanese archipelago and Sakhalin. It is bordered by Japan, North Korea, Russia and South Korea. Like the Mediterranean Sea, it has almost no tides due to its nearly complete enclosure from the Pacific...
, and Canada has a system for coastal surveillance.
Civil Aviation Radars
The post-war years saw the beginning of a revolutionary development in Air Traffic ControlAir traffic control
Air traffic control is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other...
(ATC) – the introduction of radar. In 1946, the Civil Aeronautics Administration (CAA) unveiled an experimental radar-equipped tower for control of civil flights. By 1952, the CAA had begun its first routine use of radar for approach and departure control. Four years later, it placed a large order for long-range radars for use in en route ATC; these had the capability, at higher altitudes, to see aircraft within 200 nautical miles (370 km). In 1960, it became required for aircraft flying in certain areas to carry a radar transponder
Transponder (aviation)
A transponder is an electronic device that produces a response when it receives a radio-frequency interrogation...
that identified the aircraft and helped improve radar performance. Since 1966, the responsible agency has been called the Federal Aviation Administration
Federal Aviation Administration
The Federal Aviation Administration is the national aviation authority of the United States. An agency of the United States Department of Transportation, it has authority to regulate and oversee all aspects of civil aviation in the U.S...
(FAA).
A Terminal Radar Approach Control
Terminal Control Center
A terminal radar approach control is an air traffic control facility usually located within the vicinity of a large airport. Typically, the TRACON controls aircraft within a 20-50 nautical mile radius of the major airport and a number of "satellite airports" between surface and up to between and...
(TRACON) is an ATC facility usually located within the vicinity of a large airport. In the US Air Force it is known as RAPCON (Radar Approach Control), and in the US Navy as a RATCF (Radar Air Traffic Control Facility). Typically, the TRACON controls aircraft within a 30 to 50 nautical mile (56 to 93 km) radius of the airport at an altitude between 10,000 to 15,000 feet (3,000 to 4,600 m). This uses one or more Airport Surveillance Radar
Airport Surveillance Radar
An airport surveillance radar is a radar system used at airports to detect and display the position of aircraft in the terminal area.-Digital Airport Surveillance Radar :...
s (ASR-7, 8, & 9), sweeping the sky once every few seconds.
The Digital Airport Surveillance Radar
Airport Surveillance Radar
An airport surveillance radar is a radar system used at airports to detect and display the position of aircraft in the terminal area.-Digital Airport Surveillance Radar :...
(DASR) is a newer TRACOM radar system, replacing the old analog systems with digital technology. The civilian nomenclature for this radar is the ASR-11, and AN/GPN-30 is used by the military. Two radar systems are included. The primary is an X-Band (~2.8 GHz) system with 25 kW pulse power. It provides 3-D tracking of target aircraft and also measures rainfall intensity. The secondary is a P-Band (~1.05 GHz) system with a peak-power of about 25 kW. It uses a transponder set to interrogate aircraft and receive operational data. The antennas for both systems rotate atop a tall tower.
Weather Radar
The U.S. Weather BureauNational Weather Service
The National Weather Service , once known as the Weather Bureau, is one of the six scientific agencies that make up the National Oceanic and Atmospheric Administration of the United States government...
was established in 1870 with a specific mission:
- To provide for taking meteorological observations at the military stations in the interior of the continent and at other points in the States and Territories...and for giving notice on the northern [Great] Lakes and on the seacoast by magnetic telegraph and marine signals, of the approach and force of storms.
In fulfilling this mission, the Weather Bureau established the first radio network in the United States – possibly in the world – shortly after the Galveston hurricane of 1900, one of the greatest natural disaster in America’s history. The continued use of technologies carried into the post-war era with the use of radar for meteorological monitoring. Today, the name “radar” is, to most people, tied to weather reports and warnings via the television.
The WSR-1
WSR-1
The WSR-1 or Weather Surveillance Radar-1 was one of the first weather radars. The WSR-1 series was a modified version of the AN/APS-2F radar, which the Weather Bureau acquired from the Navy. The WSR-1A, WSR-3, and WSR-4 were also variants of this radar.-----Radar Sites:...
(Weather Surveillance Radar-1) was one of the first weather radars. This was a modified version of the AN/APS-2F
AN/APS-2F
The AN/APS-2 radar began as a military aircraft radar. Some of the USA's first weather radars were modified APS-2F radars.- Radar history :The US Weather Bureau obtained 25 AN/APS-2F aircraft radars from the Navy in 1946. The radars were modified for meteorological use and put into operation at a...
radar, which the Weather Bureau acquired from the Navy. The WSR-1A, WSR-3, and WSR-4 were also variants of this radar. The Weather Bureau later became the National Weather Service
National Weather Service
The National Weather Service , once known as the Weather Bureau, is one of the six scientific agencies that make up the National Oceanic and Atmospheric Administration of the United States government...
(NWS), and is now an agency of the National Oceanic and Atmospheric Administration
National Oceanic and Atmospheric Administration
The National Oceanic and Atmospheric Administration , pronounced , like "noah", is a scientific agency within the United States Department of Commerce focused on the conditions of the oceans and the atmosphere...
(NOAA).
The WSR-57
WSR-57
WSR-57 radars were the USA's main weather surveillance radar for over 35 years. The National Weather Service operated a network of this model radar across the country, watching for severe weather.-History:...
(Weather Surveillance Radar – 1957) was the first weather radar designed specifically for a national warning network. Using WWII technology based on vacuum tubes, it gave only coarse reflectivity data and no velocity information. Operating at 2.89 GHz (S-Band), it had a peak-power of 410 kW and a maximum range of about 580 mi (933.4 km). AN/FPS-41 was the military designation for the WSR-57.
The next significant change was the WSR-74
WSR-74
WSR-74 RADARs were Weather Surveillance Radars designed in 1974 for the National Weather Service. They were added to the existing network of the WSR-57 model to improve forecasts and severe weather warnings...
series, beginning operations in 1974. There were two types: the WSR-74S, for replacements and filling gaps in the WSR-57 national network, and the WSR-74C, primarily for local use. Both were transistor-based, and their primary technical difference was indicated by the letter, S-Band (better suited for long range) and C-Band, respectively.
Until the 1990s, there were 128 of the WSR-57 and WSR-74 model radars were spread across the country in the NWS radar network. They were gradually replaced by the WSR-88D (Weather Surveillance Radar – 1988, Doppler), commonly known as NEXRAD
NEXRAD
NEXRAD or Nexrad is a network of 159 high-resolution Doppler weather radars operated by the National Weather Service, an agency of the National Oceanic and Atmospheric Administration within the United States Department of Commerce...
(Next Generation Radar). There are now over 150 NEXRAD sites networked in the United States and selected overseas locations.
The WSR-88D has a klystron
Klystron
A klystron is a specialized linear-beam vacuum tube . Klystrons are used as amplifiers at microwave and radio frequencies to produce both low-power reference signals for superheterodyne radar receivers and to produce high-power carrier waves for communications and the driving force for modern...
-based 2.7-3.0-GHz (S-Band) transmitter producing 750 kW peak-power into a parabolic-dish antenna. The PRF is selectable between 318 and 1304 Hz. The system provides reflectivity data at 0.25 km by 0.5 degree to 460 km (285.8 mi) range, and Doppler data at 0.25 km by 0.5 degree to 230 km (142.9 mi) range.
In 1998, the NWS began using the Advanced Weather Interactive Processing System
Advanced Weather Interactive Processing System
The Advanced Weather Interactive Processing System is a technologically-advanced processing, display, and telecommunications system that is the cornerstone of the United States National Weather Service's operations....
(AWIPS). This is a technologically advanced, interactive computer system that integrates data from the NEXRAD network with satellite imagery
Satellite imagery
Satellite imagery consists of photographs of Earth or other planets made by means of artificial satellites.- History :The first images from space were taken on sub-orbital flights. The U.S-launched V-2 flight on October 24, 1946 took one image every 1.5 seconds...
and surface observations for preparing forecasts and issuing warnings. With upgrades, this provides the images now well known to weather television watchers.
Mapping Radar
The plan position indicatorPlan position indicator
The plan position indicator , is the most common type of radar display. The radar antenna is usually represented in the center of the display, so the distance from it and height above ground can be drawn as concentric circles...
, dating from the early days of radar and still the most common type of display, provides a map of the targets surrounding the radar location. If the radar antenna on an aircraft is aimed downward, a map of the terrain is generated, and the larger the antenna, the greater the image resolution. After centimeter radar came into being, downward-looking radars – the H2S
H2S radar
H2S was the first airborne, ground scanning radar system. It was developed in Britain in World War II for the Royal Air Force and was used in various RAF bomber aircraft from 1943 to the 1990s. It was designed to identify targets on the ground for night and all-weather bombing...
( L-Band) and H2X
H2X radar
H2X radar was an American development of the British H2S radar, the first ground mapping radar to be used in combat. It was used by the USAAF during World War II as a navigation system for daylight overcast and nighttime operations...
(C-Band) – provided real-time maps used by the U.S. and Great Britain in bombing runs over Europe at night and through dense clouds.
In 1951, Carl Wiley led a team at Goodyear Aircraft Corporation (later Goodyear Aerospace
Goodyear Aerospace
Goodyear Aerospace Corporation was the aerospace and defense subsidiary of Goodyear.-Early Years:The company began as Goodyear Tire & Rubber Co.’s Aeronautics Department and renamed in 1917 as the Goodyear Zeppelin Corporation set up to construct dirigibles for the US military...
) in developing a technique for greatly expanding and improving the resolution of radar-generated images. Called synthetic aperture radar
Synthetic aperture radar
Synthetic-aperture radar is a form of radar whose defining characteristic is its use of relative motion between an antenna and its target region to provide distinctive long-term coherent-signal variations that are exploited to obtain finer spatial resolution than is possible with conventional...
(SAR), an ordinary-sized antenna fixed to the side of an aircraft is used with highly complex signal processing to give an image that would otherwise require a much larger, scanning antenna; thus, the name synthetic aperture. As each pulse is emitted, it is radiated over a lateral band onto the terrain. The return is spread in time, due to reflections from features at different distances. Motion of the vehicle along the flight path gives the horizontal increments. The amplitude and phase of returns are combined by the signal processor using Fourier transform
Fourier transform
In mathematics, Fourier analysis is a subject area which grew from the study of Fourier series. The subject began with the study of the way general functions may be represented by sums of simpler trigonometric functions...
techniques in forming the image. The overall technique is closely akin to optical holography
Holography
Holography is a technique that allows the light scattered from an object to be recorded and later reconstructed so that when an imaging system is placed in the reconstructed beam, an image of the object will be seen even when the object is no longer present...
.
Through the years, many variations of the SAR have been made with diversified applications resulting. In initial systems, the signal processing was too complex for on-board operation; the signals were recorded and processed later. Processors using optical techniques were then tried for generating real-time images, but advances in high-speed electronics now allow on-board processes for most applications. Early systems gave a resolution in tens of meters, but more recent airborne systems provide resolutions to about 10 cm. Current ultra-wideband
Ultra-wideband
Ultra-wideband is a radio technology that can be used at very low energy levels for short-range high-bandwidth communications by using a large portion of the radio spectrum. UWB has traditional applications in non-cooperative radar imaging...
systems have resolutions of a few millimeters.
Other Radars and Applications
There are many other post-war radar systems and applications. Only a few will be noted.Radar Gun
The most widespread radar device today is undoubtedly the radar gunRadar gun
A radar speed gun is a small doppler radar unit used to measure the speed of moving objects, including vehicles, pitched baseballs, runners and other moving objects. Radar speed guns may be hand-held, vehicle-mounted or static...
. This is a small, usually hand-held, Doppler radar
Doppler radar
A Doppler radar is a specialized radar that makes use of the Doppler effect to produce velocity data about objects at a distance. It does this by beaming a microwave signal towards a desired target and listening for its reflection, then analyzing how the frequency of the returned signal has been...
that is used to detect the speed of objects, especially trucks and automobiles in regulating traffic, as well as pitched baseballs, runners, or other moving objects in sports. This device can also be used to measure the surface speed of water and continuously manufactured materials. A radar gun does not return information regarding the object's position; it uses the Doppler effect
Doppler effect
The Doppler effect , named after Austrian physicist Christian Doppler who proposed it in 1842 in Prague, is the change in frequency of a wave for an observer moving relative to the source of the wave. It is commonly heard when a vehicle sounding a siren or horn approaches, passes, and recedes from...
to measure the speed of a target. First developed in 1954, most radar guns operate with very low power in the X or Ku Bands. Some use infrared
Infrared
Infrared light is electromagnetic radiation with a wavelength longer than that of visible light, measured from the nominal edge of visible red light at 0.74 micrometres , and extending conventionally to 300 µm...
radiation or laser
Laser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
light; these are usually called LIDAR
LIDAR
LIDAR is an optical remote sensing technology that can measure the distance to, or other properties of a target by illuminating the target with light, often using pulses from a laser...
. A related technology for velocity measurements in flowing liquids or gasses is called laser Doppler velocimetry
Laser Doppler velocimetry
Laser Doppler Velocimetry , also known as Laser Doppler Anemometry , is the technique of using the Doppler shift in a laser beam to measure the velocity in transparent or semi-transparent fluid flows, or the linear or vibratory motion of opaque, reflecting, surfaces.-Technology origin:With the...
; this technology dates from the mid-1960s.
Impulse Radar
As pulsed radars were initially being developed, the use of very narrow pulses was examined. The pulse length governs the accuracy of distance measurement by radar – the shorter the pulse, the greater the precision. Also, for a given pulse repetition frequencyPulse repetition frequency
Pulse repetition frequency or Pulse repetition rate is the number of pulses per time unit . It is a measure or specification mostly used within various technical disciplines Pulse repetition frequency (PRF) or Pulse repetition rate (PRR) is the number of pulses per time unit (e.g. Seconds). It...
(PRF), a shorter pulse results in a higher peak power. Harmonic analysis
Harmonic analysis
Harmonic analysis is the branch of mathematics that studies the representation of functions or signals as the superposition of basic waves. It investigates and generalizes the notions of Fourier series and Fourier transforms...
shows that the narrower the pulse, the wider the band of frequencies that contain the energy, leading to such systems also being called wide-band radars. In the early days, the electronics for generating and receiving these pulses was not available; thus, essentially no applications of this were initially made.
By the 1970s, advances in electronics led to renewed interest in what was often called short-pulse radar. With further advances, it became practical to generate pulses having a width on the same order as the period of the RF carrier (T = 1/f). This is now generally called impulse radar.
The first significant application of this technology was in ground-penetrating radar
Ground-penetrating radar
Ground-penetrating radar is a geophysical method that uses radar pulses to image the subsurface. This nondestructive method uses electromagnetic radiation in the microwave band of the radio spectrum, and detects the reflected signals from subsurface structures...
(GPR). Developed in the 1970s, GPR is now used for structural foundation analysis, archeological mapping, treasure hunting, unexploded ordinance identification, and other shallow investigations. This is possible because impulse radar can concisely locate the boundaries between the general media (the soil) and the desired target. The results, however, are non-unique and are highly dependant upon the skill of the operator and the subsequent interpretation of the data.
In dry or otherwise favorable soil and rock, penetration up to 300 feet (91.4 m) is often possible. For distance measurements at these short ranges, the transmitted pulse is usually only one radio-frequency cycle in duration; With a 100 MHz carrier and a PRF of 10 kHz (typical parameters), the pulse duration is only 10 ns (nanosecond). leading to the "impulse" designation. A variety of GPR systems are commercially available in back-pack and wheeled-cart versions with pulse-power up to a kilowatt.
With continued development of electronics, systems with pulse durations measured in picosecond
Picosecond
A picosecond is 10−12 of a second. That is one trillionth, or one millionth of one millionth of a second, or 0.000 000 000 001 seconds. A picosecond is to one second as one second is to 31,700 years....
s became possible. Applications are as varied as security and motion sensors, building stud-finders, collision-warning devices, and cardiac-dynamics monitors. Some of these devices are match-box sized, including a long-life power source.
Radar Astronomy
As radar was being developed, astronomers considered its application in making observations of the Moon and other near-by extraterrestrial objects. In 1944, Zoltán Lajos BayZoltán Lajos Bay
Zoltán Lajos Bay was a Hungarian physicist, professor, and engineer who developed microwave technology, including tungsten lamps. He was the first person to observe radar echoes from the Moon...
had this as a major objective as he developed a radar in Hungary. Sadly, his radar telescope was taken away by the conquering Soviet army and had to be rebuilt, thus delaying the experiment. Under Project Diana
Project Diana
Project Diana, named for the Roman moon goddess Diana — goddess of the hunt, wild animals and the moon — was a project of the US Army Signal Corps to bounce radio signals off the moon and receive the reflected signals...
conducted by the Army’s Evans Signal Laboratory in New Jersey, a modified SCR-271 radar (the fixed-position version of the SCR-270
SCR-270 radar
The SCR-270 was one of the first operational early warning radars. It was the U.S. Army's primary long-distance radar throughout World War II and was deployed around the world...
) operating at 110 MHz with 3 kW peak-power, was used in receiving echoes from the Moon on January 10, 1946. Zoltán Bay accomplished this on the following February 6.
Radio astronomy
Radio astronomy
Radio astronomy is a subfield of astronomy that studies celestial objects at radio frequencies. The initial detection of radio waves from an astronomical object was made in the 1930s, when Karl Jansky observed radiation coming from the Milky Way. Subsequent observations have identified a number of...
also had its start following WWII, and many scientists involved in radar development then entered this field. A number of radio observatories were constructed during the following years; however, because of the additional cost and complexity of involving transmitters and associated receiving equipment, very few were dedicated to radar astronomy. In fact, essentially all major radar astronomy activities have been conducted as adjuncts to radio astronomy observatories.
The radio telescope
Radio telescope
A radio telescope is a form of directional radio antenna used in radio astronomy. The same types of antennas are also used in tracking and collecting data from satellites and space probes...
at the Arecibo Observatory
Arecibo Observatory
The Arecibo Observatory is a radio telescope near the city of Arecibo in Puerto Rico. It is operated by SRI International under cooperative agreement with the National Science Foundation...
, opened in 1963, is the largest in the world. Owned by the U.S. National Science Foundation
National Science Foundation
The National Science Foundation is a United States government agency that supports fundamental research and education in all the non-medical fields of science and engineering. Its medical counterpart is the National Institutes of Health...
and contractor operated, it is used primarily for radio astronomy, but equipment is available for radar astronomy. This includes transmitters operating at 47 MHz, 439 MHz, and 2.38 GHz, all with very-high pulse power. It has a 305-m (1,000-ft) primary reflector
Primary mirror
A primary mirror is the principal light-gathering surface of a reflecting telescope.-Description:The primary mirror of a reflecting telescope is a spherical or parabolic shaped disks of polished reflective metal , or in later telescopes, glass or other material coated with a reflective layer...
fixed in position; the secondary reflector
Secondary mirror
A secondary mirror is the second deflecting or focusing mirror element in a reflecting telescope. Light gathered by the primary mirror is directed towards a focal point typically past the location of the secondary. Secondary mirrors in the form of an optically flat diagonal mirror are used to...
is on tracks to allow precise pointing to different parts of the sky. Many significant scientific discoveries have been made using the Arecibo radar telescope, including mapping of surface roughness of Mars
Mars
Mars is the fourth planet from the Sun in the Solar System. The planet is named after the Roman god of war, Mars. It is often described as the "Red Planet", as the iron oxide prevalent on its surface gives it a reddish appearance...
and observations of Saturn
Saturn
Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Saturn is named after the Roman god Saturn, equated to the Greek Cronus , the Babylonian Ninurta and the Hindu Shani. Saturn's astronomical symbol represents the Roman god's sickle.Saturn,...
s and its largest moon, Titan
Titan (moon)
Titan , or Saturn VI, is the largest moon of Saturn, the only natural satellite known to have a dense atmosphere, and the only object other than Earth for which clear evidence of stable bodies of surface liquid has been found....
. In 1989, the observatory radar-imaged an asteroid
Asteroid
Asteroids are a class of small Solar System bodies in orbit around the Sun. They have also been called planetoids, especially the larger ones...
for the first time in history.
Several spacecraft orbiting the Moon, Mercury, Venus, Mars, and Saturn have carried radars for surface mapping; a ground-penetration radar was carried on the Mars Express
Mars Express
Mars Express is a space exploration mission being conducted by the European Space Agency . The Mars Express mission is exploring the planet Mars, and is the first planetary mission attempted by the agency. "Express" originally referred to the speed and efficiency with which the spacecraft was...
mission. Radar systems on a number of aircraft and orbiting spacecraft have mapped the entire Earth for various purposes; on the Shuttle Radar Topography Mission
Shuttle Radar Topography Mission
The Shuttle Radar Topography Mission is an international research effort that obtained digital elevation models on a near-global scale from 56° S to 60° N, to generate the most complete high-resolution digital topographic database of Earth prior to the release of the ASTER GDEM in 2009...
, the entire planet was mapped at a 30-m resolution.
The Jodrell Bank Observatory, an operation of the University of Manchester
University of Manchester
The University of Manchester is a public research university located in Manchester, United Kingdom. It is a "red brick" university and a member of the Russell Group of research-intensive British universities and the N8 Group...
in Great Britain, was originally started by Bernard Lovell
Bernard Lovell
Sir Alfred Charles Bernard Lovell OBE, FRS is an English physicist and radio astronomer. He was the first Director of Jodrell Bank Observatory, from 1945 to 1980.-Early Life:...
to be a radar astronomy facility. It initially used a war-surplus GL-II radar system operating at 71 MHz (4.2 m). The first observations were of ionized trails in the Geminids
Geminids
The Geminids are a meteor shower caused by the object 3200 Phaethon, which is thought to be a Palladian asteroid. This would make the Geminids, together with the Quadrantids, the only major meteor showers not originating from a comet...
meteor shower during December 1945. While the facility soon evolved to become the third largest radio observatory in the world, some radar astronomy continued. The largest (250-ft or 76-m in diameter) of their three fully steerable radio telescopes became operational just in time to radar track Sputnik 1
Sputnik 1
Sputnik 1 ) was the first artificial satellite to be put into Earth's orbit. It was launched into an elliptical low Earth orbit by the Soviet Union on 4 October 1957. The unanticipated announcement of Sputnik 1s success precipitated the Sputnik crisis in the United States and ignited the Space...
, the first artificial satellite, in October 1957.
See also
- List of World War II electronic warfare equipment
- Secrets of Radar MuseumSecrets of Radar MuseumThe Secrets of Radar Museum is a small military museum located near Parkwood Hospital in London, Ontario, Canada. Founded in 2003, the museum exists to tell the story of the more than 6,000 Canadian World War II veterans who were recruited into a top-secret project during World War II involving...
- German inventors and discoverersGerman inventors and discoverersThis is a list of German inventors and discoverers. The following list comprises people from Germany or German-speaking Europe, also of people of predominantly German heritage, in alphabetical order of the surname. The main section includes existing articles, indicated by blue links, and possibly...
Further reading
- Blanchard, Yves, Le radar. 1904-2004 : Histoire d'un siècle d'innovations techniques et opérationnelles, éditions Ellipses,(in French)
- Bowen, E. G.; “The development of airborne radar in Great Britain 1935-1945,” in Radar Development to 1945, ed. by Russell Burns; Peter Peregrinus, 1988, ISBM 0-86341-139-8
- Bowen, E. G., Radar Days, Institute of Physics Publishing, Bristol, 1987, ISBN 0-7503-0586-X
- Bragg, Michael., RDF1 The Location of Aircraft by Radio Methods 1935-1945, Hawkhead Publishing, 1988, ISBN 0-9531544-0-8
- Brown, Jim, Radar - how it all began, Janus Pub., 1996, ISBN 1-85756-212-7
- Brown, Louis, A Radar History of World War 2 - Technical and Military Imperatives, Institute of Physics Publishing, 1999, ISBN 0-7503-0659-9
- Buderi, Robert: The invention that changed the world: the story of radar from war to peace, Simon & Schuster, 1996, ISBN 0-349-11068-9
- Burns, Peter (editor): Radar Development to 1945, Peter Peregrinus Ltd., 1988, ISBN 0-86341-139-8
- Clark, Ronald W., Tizard, MIT Press, 1965, ISBN 0-262-03010-1 (An authorized biography of radar's champion in the 1930s.)
- Dummer, G. W. A., Electronic Inventions and Discoveries, Elsevier, 1976, Pergamon, 1977, ISBN 0-802-0982-3
- Erickson, John; “Radio-location and the air defense problem: The design and development of Soviet Radar 1934-40,” Social Studies of Science, vol. 2, p. 241, 1972
- Frank, Sir Charles, Operation Epsilon: The Farm Hall Transcripts U. Cal. Press, 1993 (How German scientists dealt with Nazism.)
- Guerlac, Henry E., Radar in World War II,(in two volumes), Tomash Publishers / Am Inst. of Physics, 1987, ISBN 0-88318-486-9
- Hanbury Brown, Robert, Boffin: A Personal Story of the early Days of Radar and Radio Astronomy and Quantum Optics, Taylor and Francis, 1991, ISBM 0-750-030130-9
- Howse, Derek, Radar At Sea The Royal Navy in World War 2, Naval Institute Press, Annapolis, Maryland, USA, 1993, ISBN 1-55750-704-X
- Jones, R. V., Most Secret War, Hamish Hamilton, 1978, ISBN 0-340-24169-1 (Account of British Scientific Intelligence between 1939 and 1945, working to anticipate Germany's radar and other developments.)
- Kroge, Harry von, GEMA: Birthplace of German Radar and Sonar, translated by Louis Brown, Inst. of Physics Publishing, 2000, ISBN 0-471-24698-0
- Latham, Colin & Stobbs, Anne., Radar A Wartime Miracle, Sutton Publishing Ltd, Stroud 1996, ISBN 0-7509-1643-5 (A history of radar in the UK during WWII told by the men and women who worked on it.)
- Latham, Colin, and Anne Stobbs, The Birth of British Radar: The Memoirs of Arnold 'Skip' WilkinsArnold Frederic WilkinsArnold Frederic Wilkins O.B.E., was a pioneer in developing the use of radar.-Early life:...
, Speedwell for the Defence Electronics History Society 2006, ISBN 0-9537166-2-7 - Lovell, Sir Bernard Lovel, Echoes of War - The History of H2S, Adam Hilger, 1991, ISBN 0-85274-317-3
- Nakagawa, Yasudo; Japanese Radar and Related Weapons of World War II, translated and edited by Louis Brown, John Bryant, and Naohiko Koizumi, Aegean Park Press, 1997, ISBN 0-89412-271-1
- Pritchard, David., The Radar War Germany's Pioneering Achievement 1904-1945 Patrick Stephens Ltd, Wellingborough 1989, ISBN 1-85260-246-5
- Rawnsley, C. F., and Robert Wright, Night Fighter, Mass Mktng Papetback, 1998
- Sayer, A. P., Army Radar - historical monograph, War Office, 1950
- Swords, Seán S., Technical History of the Beginnings of Radar, IEE/Peter Peregrinus, 1986, ISBN 0-86341-043-X
- Watson, Raymond C., Jr. Radar Origins Worldwide: History of Its Evolution in 13 Nations Through World War II. Trafford Pub., 2009, ISBN 978-1-4269-2111-7
- Watson-Watt, Sir Robert, The Pulse of Radar, Dial Press, 1959, (no ISBN) (An autobiography of Sir Robert Watson-Watt)
- Zimmerman, David., Britain's Shield Radar and the Defeat of the Luftwaffe, Sutton Publishing, 2001, ISBN 0-7509-1799-7
External links
- Author unknown,
- Barrett, Dick, "All you ever wanted to know about British air defence radar". The Radar Pages. (History and details of various British radar systems)
- Clark, Maj. Gregory C., Deflating British Radar Myths of World War II, 1997, http://www.radarpages.co.uk/download/AUACSC0609F97-3.pdf
- Hollmann, Martin, "Radar Family Tree". Radar World.
- ES310 "Introduction to Naval Weapons Engineering." (Radar fundamentals section)
- The first operational radar in France 1934 http://www.radar-france.fr
- Penley, Bill, and Jonathan Penley, "Early Radar History - an Introduction". 2002.
- Buderi,Robert, "Telephone History: Radar History". Privateline.com. (Anecdotal account of the carriage of the world's first high power cavity magnetron from Britain to the US during WW2.)
- Romano, Salvatore; http://www.regiamarina.net/others/radar/radar_one_us.htm “History of the Development of Radar in Italy,” Regia Marina Italiana [Royal Italian Navy], 2004;
- Sinnott, D.H., "The Development of Over-the-Horizon Radar in Australia"
- The Secrets of Radar Museum (Canada's involvement in WWII Radar)
- The Radar Pages
- The Wizard War: WW2 & The Origins Of Radar (From Greg Goebel's In The Public Domain)
- German Radar Equipment of World War II
- Early radar development in the UK
- A History of Radio Location in the USSR (In Russian)