Discone antenna
Encyclopedia
Biconical antenna
In radio systems, a biconical antenna is a broad-bandwith antenna made of two roughly conical conductive objects, nearly touching at their points. Biconical antennas are broadband dipole antennas, typically exhibiting a bandwidth of 3 octaves or more....
in which one of the cones is replaced by a disc. It is usually mounted vertically, with the disc at the top and the cone beneath.
Omnidirectional
Omnidirectional antenna
In radio communication, an omnidirectional antenna is an antenna which radiates radio wave power uniformly in all directions in one plane, with the radiated power decreasing with elevation angle above or below the plane, dropping to zero on the antenna's axis. This radiation pattern is often...
, vertically polarized and exhibiting unity gain
Antenna gain
In electromagnetics, an antenna's power gain or simply gain is a key performance figure which combines the antenna's directivity and electrical efficiency. As a transmitting antenna, the figure describes how well the antenna converts input power into radio waves headed in a specified direction...
, it is exceptionally wideband
Wideband
In communications, wideband is a relative term used to describe a wide range of frequencies in a spectrum. A system is typically described as wideband if the message bandwidth significantly exceeds the channel's coherence bandwidth....
, offering a frequency range ratio of up to ~10:1. The radiation pattern
Radiation pattern
In the field of antenna design the term radiation pattern most commonly refers to the directional dependence of the strength of the radio waves from the antenna or other source ....
in the horizontal plane
Horizontal plane
In geometry, physics, astronomy, geography, and related sciences, a plane is said to be horizontal at a given point if it is perpendicular to the gradient of the gravity field at that point— in other words, if apparent gravity makes a plumb bob hang perpendicular to the plane at that point.In...
is quite narrow, making its sensitivity
Sensitivity (electronics)
The sensitivity of an electronic device, such as a communications system receiver, or detection device, such as a PIN diode, is the minimum magnitude of input signal required to produce a specified output signal having a specified signal-to-noise ratio, or other specified criteria.Sensitivity is...
highest in the plane tangent to the Earth's surface.
History
On February 6, 1945, Armig G. Kandoian of New YorkNew York
New York is a state in the Northeastern region of the United States. It is the nation's third most populous state. New York is bordered by New Jersey and Pennsylvania to the south, and by Connecticut, Massachusetts and Vermont to the east...
was awarded U.S. patent number 2,368,663 (assignor to Federal Telephone and Radio Corporation (later merged with ITT Corporation
ITT Corporation
ITT Corporation is a global diversified manufacturing company based in the United States. ITT participates in global markets including water and fluids management, defense and security, and motion and flow control...
) for a "broad band antenna", from an application made on May 15, 1943.
Excerpt from the Kandoian patent:
In keeping with progress made during the last few years in the development of ultra-high frequencyUltra high frequencyUltra-High Frequency designates the ITU Radio frequency range of electromagnetic waves between 300 MHz and 3 GHz , also known as the decimetre band or decimetre wave as the wavelengths range from one to ten decimetres...
radioRadioRadio is the transmission of signals through free space by modulation of electromagnetic waves with frequencies below those of visible light. Electromagnetic radiation travels by means of oscillating electromagnetic fields that pass through the air and the vacuum of space...
technique, and applications thereof to aircraftAircraftAn aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
communication, direction findingDirection findingDirection finding refers to the establishment of the direction from which a received signal was transmitted. This can refer to radio or other forms of wireless communication...
, and so forth, it has become necessary to develop special antennas and antenna systems suitable for installation on such aircraft. Flying conditions are such that these antennas must necessarily be small and rigid in their construction and also offer a minimum of wind resistanceDrag (physics)In fluid dynamics, drag refers to forces which act on a solid object in the direction of the relative fluid flow velocity...
, in order that the flying efficiency of the aircraft will be unimpaired. In accordance with my invention I have provided a small rigid antenna suitable for mounting on the surface of the fuselageFuselageThe fuselage is an aircraft's main body section that holds crew and passengers or cargo. In single-engine aircraft it will usually contain an engine, although in some amphibious aircraft the single engine is mounted on a pylon attached to the fuselage which in turn is used as a floating hull...
or other component of the airplane structure and in certain embodiments I have also provided a streamlined protecting shield or housing covering or so cooperating with the construction of the antenna system as to greatly reduce wind resistance.
Applications
The discone's wideband coverage makes it attractive in commercial, military, amateur radioAmateur radio
Amateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
and radio scanner
Scanner (radio)
A scanner is a radio receiver that can automatically tune, or scan, two or more discrete frequencies, stopping when it finds a signal on one of them and then continuing to scan other frequencies when the initial transmission ceases....
applications.
When employed as a transmitting antenna, it is often less efficient than an antenna designed for a more limited frequency range. SWR (standing wave ratio
Standing wave ratio
In telecommunications, standing wave ratio is the ratio of the amplitude of a partial standing wave at an antinode to the amplitude at an adjacent node , in an electrical transmission line....
) is typically ~2:1 over the range of the design frequency to the second harmonic and ~3.1 thereafter.
The discone's inherently wideband nature permits it to broadcast undesirable spurious emission
Spurious emission
A spurious emission is any radio frequency not deliberately created or transmitted, especially in a device which normally does create other frequencies...
s from faulty or improperly filtered transmitters.
Construction materials
A discone may be made from solid metal sheet (often copperCopper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...
), which is practical for small indoor UHF antennas, such as for Wi-Fi
Wi-Fi
Wi-Fi or Wifi, is a mechanism for wirelessly connecting electronic devices. A device enabled with Wi-Fi, such as a personal computer, video game console, smartphone, or digital audio player, can connect to the Internet via a wireless network access point. An access point has a range of about 20...
.
At lower frequencies a sufficient number of metal wires or rods in a spoke
Spoke
A spoke is one of some number of rods radiating from the center of a wheel , connecting the hub with the round traction surface....
configuration is often used to approximate a solid surface. This simplifies construction and reduces wind loading.
The spokes may be made of stiff wire, brazing rods or even coat hanger wire.
The optimal number of rods comprising the disc and cone is often quoted as being from 8 to 16.
Components
A discone antenna typically has at least three major components: the disc, the cone, and the insulator.The disc
The disc should have an overall diameter of 0.7 times a quarter wavelengthWavelength
In physics, the wavelength of a sinusoidal wave is the spatial period of the wave—the distance over which the wave's shape repeats.It is usually determined by considering the distance between consecutive corresponding points of the same phase, such as crests, troughs, or zero crossings, and is a...
of the antenna's minimum frequency
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
.
The antenna's feed point is at the center of the disc. It is usually fed with 50-ohm coaxial cable
Coaxial cable
Coaxial cable, or coax, has an inner conductor surrounded by a flexible, tubular insulating layer, surrounded by a tubular conducting shield. The term coaxial comes from the inner conductor and the outer shield sharing the same geometric axis...
, with the center conductor connected to the disc, and the outer conductor to the cone.
The cone
The length of the cone should be a quarter wavelength of the antenna's minimum operating frequency.The cone angle is generally from 25 to 40 degrees.
The insulator
The disc and cone must be separated by an insulator, the dimensions of which determine some of the antenna's properties.Extending low-frequency response
A vertical whip may be placed affixed vertically to the disc in order to extend the low frequency response, but this may reduce efficiency at higher frequencies. In this configuration, at lower frequencies the discone may more closely resemble a ground plane antennaGround plane
In electrical engineering, a ground plane is an electrically conductive surface.-Radio antenna theory :In telecommunication, a ground plane structure or relationship exists between the antenna and another object, where the only structure of the object is a structure which permits the antenna to...
or a coaxial dipole
Coaxial antenna
A coaxial antenna is a particular form of a half-wave dipole antenna, most often employed as a vertically polarized omnidirectional antenna.-History:Arnold B...
.
See also
- Antennas
- Biconical antennaBiconical antennaIn radio systems, a biconical antenna is a broad-bandwith antenna made of two roughly conical conductive objects, nearly touching at their points. Biconical antennas are broadband dipole antennas, typically exhibiting a bandwidth of 3 octaves or more....
- Very high frequencyVery high frequencyVery high frequency is the radio frequency range from 30 MHz to 300 MHz. Frequencies immediately below VHF are denoted High frequency , and the next higher frequencies are known as Ultra high frequency...
- Ultra high frequencyUltra high frequencyUltra-High Frequency designates the ITU Radio frequency range of electromagnetic waves between 300 MHz and 3 GHz , also known as the decimetre band or decimetre wave as the wavelengths range from one to ten decimetres...
- Scanner (radio)Scanner (radio)A scanner is a radio receiver that can automatically tune, or scan, two or more discrete frequencies, stopping when it finds a signal on one of them and then continuing to scan other frequencies when the initial transmission ceases....
- Amateur radioAmateur radioAmateur radio is the use of designated radio frequency spectrum for purposes of private recreation, non-commercial exchange of messages, wireless experimentation, self-training, and emergency communication...
External links
- Kandoian's patent
- Discone design program
- Tim's Discone Antenna
- UHF Discone Antenna
- The Discone Antenna
- Parabolic Discone (Michael Lake KD8CIK)
- Highest Gain Discone Antenna Ever (Michael Lake (KD8CIK) - eham.net discussion of above
- VHF/UHF Discones
- text and construction hints
- Broadband radial discone antenna: Design, application and measurements
- Antenna Magus Antenna Magus, an antenna design tool, contains a Discone antenna.