Antenna factor

In telecommunications, the antenna factor "AF" (unit: 1/m) is defined as the ratio of the incident electromagnetic field strength "E" (units: V/m or µV/m) to the voltage "V" (units: V or µV) on the line connection of an antenna:

: $AF\; =\; frac\; EV$

If all quantities are expressed logarithmically in decibels instead of SI units, the above equation becomes

: $AF\_\{mathrm\{dBm\}^\{-1\; =E\_mathrm\{mathrm\{dBV/m\; -\; V\_\{mathrm\{dBV\; =E\_mathrm\{mathrm\{dB\}mumathrm\{V/m\; -\; V\_\{mathrm\{dB\}mumathrm\{V$

In a 50 Ω system, the antenna factor is related to the antenna gain "G" and the wavelength λ via:

: $AF\; =\; frac\{9.73\}\{lambda\; sqrt\{G\}\; \}$

The variable G means antenna gain (dimensionless) and it can be written in terms of effective aperture A to obtain the final expression considering the impedance of free space (376.6Ω) and the load as 50Ω. The antenna effective aperture can be written as A = (λ²G)/4π.

References

* [http://www.microindustrie.com/fcc/recaf.htm MicroIndustrie Antenna Factor] (link broken)
* [http://www.djmelectronics.com/articles/emc-antenna-parameters-p3.html Interpreting Antenna Performance Parameters for EMC Applications] An excellent page with summaries of all the relevant equations