Reference antenna
Encyclopedia
A reference antenna is an antenna
with known performance. It is normally used to calibrate other systems.
Reference antennas are built with particular care taken to make them simple, robust and repeatable. In a common usage scenario a reference antenna would be used as a transfer standard. First the reference antenna's performance is measured using high accuracy measurement facility. This test may be done using an Electromagnetic Anechoic chamber
or another type of Antenna Test Range (see Antenna Measurements). The antenna is then measured using a second antenna test facility. The results from the two are compared, the comparison can reveal the accuracy of the second test facility. It can also be used to calibrate the second facility.
Sometimes rather than measure the performance of the reference antenna theoretical methods are used. The antenna may be simulated using electromagnetic simulation, or its properties derived from formulae based on electromagnetic theory. These methods are only useful if the materials and dimensions of the antenna can be characterised very well, and the mathematics of the simulation or formulae used is known to be accurate.
Normally the parameter of interest is antenna gain
. In this case the reference antenna is built to have a high degree of repeatability
in its radiation pattern
and boresight
gain. A common practice is to measure the boresight gain of a reference antenna across its operational frequency band. Other parameters are sometimes of interest though, such as antenna efficiency.
Common reference antennas are Horns
, dipoles
, monopoles
and Biconicals
. These types are chosen because they are mechanically simple and quite electrically simple. Mechanical simplicity makes building repeatable antennas easier. Electrical simplicity makes design easier and allows use of design formulae that are known to be accurate.
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...
with known performance. It is normally used to calibrate other systems.
Reference antennas are built with particular care taken to make them simple, robust and repeatable. In a common usage scenario a reference antenna would be used as a transfer standard. First the reference antenna's performance is measured using high accuracy measurement facility. This test may be done using an Electromagnetic Anechoic chamber
Anechoic chamber
An anechoic chamber is a room designed to stop reflections of either sound or electromagnetic waves.They are also insulated from exterior sources of noise...
or another type of Antenna Test Range (see Antenna Measurements). The antenna is then measured using a second antenna test facility. The results from the two are compared, the comparison can reveal the accuracy of the second test facility. It can also be used to calibrate the second facility.
Sometimes rather than measure the performance of the reference antenna theoretical methods are used. The antenna may be simulated using electromagnetic simulation, or its properties derived from formulae based on electromagnetic theory. These methods are only useful if the materials and dimensions of the antenna can be characterised very well, and the mathematics of the simulation or formulae used is known to be accurate.
Normally the parameter of interest is antenna gain
Gain
In electronics, gain is a measure of the ability of a circuit to increase the power or amplitude of a signal from the input to the output. It is usually defined as the mean ratio of the signal output of a system to the signal input of the same system. It may also be defined on a logarithmic scale,...
. In this case the reference antenna is built to have a high degree of repeatability
Repeatability
Repeatability or test-retest reliability is the variation in measurements if they would have been taken by a single person or instrument on the same item and under the same conditions. A less-than-perfect test-retest reliability causes test-retest variability. Such variability can be caused by, for...
in its 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 ....
and boresight
Boresight
Boresight is a term used to describe crude adjustments made to an optical firearm sight, or iron sights, to align the firearm barrel and sights. This method is usually used to pre-align the sights, which makes zeroing much faster.Traditional boresighting, as the name suggests involves removing...
gain. A common practice is to measure the boresight gain of a reference antenna across its operational frequency band. Other parameters are sometimes of interest though, such as antenna efficiency.
Common reference antennas are Horns
Horn antenna
A horn antenna or microwave horn is an antenna that consists of a flaring metal waveguide shaped like a horn to direct the radio waves. Horns are widely used as antennas at UHF and microwave frequencies, above 300 MHz...
, dipoles
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...
, monopoles
Monopole antenna
A monopole antenna is a class of radio antenna consisting of a straight rod-shaped conductor, often mounted perpendicularly over some type of conductive surface, called a ground plane. The driving signal from the transmitter is applied, or for receiving antennas the output voltage is taken,...
and Biconicals
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....
. These types are chosen because they are mechanically simple and quite electrically simple. Mechanical simplicity makes building repeatable antennas easier. Electrical simplicity makes design easier and allows use of design formulae that are known to be accurate.