# Antenna factor

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

: $AF_\left\{mathrm\left\{dBm\right\}^\left\{-1 =E_mathrm\left\{mathrm\left\{dBV/m - V_\left\{mathrm\left\{dBV =E_mathrm\left\{mathrm\left\{dB\right\}mumathrm\left\{V/m - V_\left\{mathrm\left\{dB\right\}mumathrm\left\{V$

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

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

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

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