Antenna gain is usually defined as the ratio of the power produced by the antenna from a far-field source on the antenna's beam axis to the power produced by a hypothetical lossless isotropic antenna, which is equally sensitive to signals from all directions.
Two direct methods of measuring the Rx gain can be used; integration of the Rx sidelobe pattern or by determination of the 3dB and 10dB beamwidths.
The use of pattern integration will produce the more accurate results but would require the AUT to have a tracking system. In both cases the test configurations for measuring Rx gain are identical, and are illustrated in Figure.
In order to measure the Rx gain using pattern integration the AUT measures the elevation and azimuth narrowband (±5° corrected) sidelobe patterns.
The AUT then calculates the directive gain of the antenna through integration of the sidelobe patterns. The Rx gain is then determined by reducing the directive gain by the antenna inefficiencies.
In order to measure the Rx gain using the beamwidth method, the AUT measures the corrected azimuth and elevation 3dB/10dB beamwidths. From these results the Rx gain of the antenna can be directly calculated using the formula below.
G is the effective antenna gain (dBi)
Az3 is the corrected azimuth 3dB beamwidth (°)
El3 is the elevation 3dB beamwidth (°)
Az10 is the corrected azimuth 10dB beamwidth (°)
El10 is the elevation 10dB beamwidth (°)
FLoss is the insertion loss of the feed (dB)
RLoss is the reduction in antenna gain due to reflector inaccuracies, and is given
RLoss =4.922998677(Sdev f )2 dB
where: Sdev is the standard deviation of the actual reflector surface (inches)
f is the frequency (GHz)