This tool calculates the Antenna Factor (AF) from the Antenna Gain (G) and Frequency of operation (f).
Formula
AF = 20*Log10(9.73/(λ√G))
where,
λ = c/f
c is the speed of light, f is the operating frequency and λ is the wavelength
and
G is the linear value of Antenna Gain relative to that of an isotropic antenna.
How to use the Calculator
Enter
- Antenna gain (in dBi) – this is typically provided by manufacturers in the data-sheet
- Frequency of operation (in MHz)
Example calculation: for a gain of 8 dBi and frequency of 915 MHz, the Antenna Factor is 21.50 dB/m.
Increasing the antenna gain to 12 dBi at the same frequency gives a lower value of AF = 17.5 dB/m
Background
Antenna Factor is the ratio of the electric field E (units: V/m or μV/m) to the voltage V (units: V or μV) induced across the terminals of an antenna. It is a measure of how much energy is captured by the antenna.
For a fixed value of E, a higher Antenna Factor implies a smaller effective voltage. This translates to a lower antenna gain in dBi.
The units are dB-per-meter or dB/m.
Notes
The equation for Antenna Factor takes the effect of impedance mismatch into account and only applies under the following conditions
- When the receiving antenna is in the far field of the transmitter
- Impedance is 50 ohm
- Antenna and incident field is matched in terms of polarization