Friis Transmission equation
The Friis transmission equation is used in telecommunications engineering, and gives the power received by one antenna under idealized conditions given another antenna some distance away transmitting a known amount of power. The formula was derived in 1945 by Danish-American radio engineer Harald T. Friis at Bell Labs.
n its simplest form, the Friis transmission equation is as follows. Given two antennas, the ratio of power available at the input of the receiving antenna, P_r, to output power to the transmitting antenna, P_t, is given by the formula show here.
The inverse of the third factor is the so-called free-space path loss. To use the equation as written, the antenna gain may not be in units of decibels, and the wavelength and distance units must be the same.Related formulas
|Pr||power available at the input of the receiving antenna (watt)|
|Pt||output power to the transmitting antenna (watt)|
|Gt||antenna gain (with respect to an isotropic radiator) of the transmitting antennas (dimensionless)|
|Gr||antenna gain (with respect to an isotropic radiator) of the receiving antennas (dimensionless)|
|R||distance between the antennas (m)|