Gain parameters are commonly used to model the performance of both and transmit and receive antenna, but Antenna Factors are normally only used to model the performance of transmit antenna (which are more precise than receive only units).

While it may seem odd to specify AF for a receive antenna it starts to make sense when you are using calibrated EMC antenna for all TSCM procedures.

Of course antenna factors increase with frequency (as does gain), and remember that Antenna Factor is different from Transmit Antenna Factor (so be careful). (Antenna Factor is calculated as AF = Electric Field/Voltage applied to Antenna and is normally expressed in dB).

Remember that while Gain is commonly used to describe the directional response, AF is used to describe how "clean" the antenna is.

The high threat VHF band should be checked using an antenna factor of at least 10 dB 1/m for signals between 20 MHz and 300 MHz. Antenna gain should be between unity and 4 dB over this range.

Antenna factors for frequencies above 300 MHz should be between (at least) 15 and 20 dB 1/m. Antenna gain should be over 4-8 dB from 300 MHz to 1 GHz.

At frequencies above 900 MHz it is desirable to use an antenna which offers a factor of at least 25 dB 1/m, and 30 dB 1/m above 2 GHz. Antenna gain should be at least 8-10 dB above 900 MHz (a gain of at least 15 dB is preferred). A gain of at least 15 dB is recommended between 1.2 GHz and 3 GHz.

From 3 GHz to 12 GHz an antenna factor of between 30 to 40 dB 1/m is good, but anything above 12 GHz requires at least 40 dB 1/m of antenna factor or it will be virtually impossible to detect the signal. Antenna gain should be at least 8 dB over this range. A gain of at least 20 dB is recommended between 3 GHz to 6 GHz, and at least 30 dB up to 12 GHz.

Above 12 GHz antenna factors of at least 35 dB 1/m must be considered. A gain of at least 50 dB should be used when dealing with frequencies in this range.

The antenna being used must be operated in both a horizontal and vertical polarized position, and also in a 45-degree diagonal position for optimal signal detection.

Left and Right Handed Polarized signals should be checked between 900 MHz and 12 GHz using an antenna factor of at least 25 dB 1/m and a gain of 2-4 dB. Remember that you will get a polarization offset loss figure that must be taken into consideration when using a linear polarized antenna.

The number of antenna azimuth and elevation positions used will of course be directly related to the gain of the specific antenna.

A good rule of thumb is that in a 10-meter by 10-meter square room in an office environment to use at least 16 steps (22.5 degrees) along each axis for every 10 dB of antenna gain. For a typical log periodic antenna (with 5 dB of gain) this would result in 64 measurement positions for each polarization for a total of 320 positions (assuming horizontal, vertical, diagonal, LHCP, and RHCP polarization). Needless to say a small computer controlled antenna positioning system is most helpful.