# Friis Transmission equation (with dB units)

## Description

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.

If the gain has units of dB, the equation is as shown here.

Related formulas## Variables

P_{r} | power available at the input of the receiving antenna(in dBm) (dimensionless) |

P_{t} | output power to the transmitting antenna(in dBm) (dimensionless) |

G_{t} | antenna gain (with respect to an isotropic radiator) of the transmitting antennas (decibel) |

G_{r} | antenna gain (with respect to an isotropic radiator) of (decibel) |

λ | wavelength (m) |

π | pi |

R | distance between the antennas (m) |