# Friis Equation

Friis Equation calculates the power that is received by one antenna from another when transmitted from a distance at a frequency. It states that antenna gains energy when path loss is higher. Here Friis Transmission Formula is given to calculate the ratio of the input and output of transmitted powers. It computes the transmission of signals between two antennas using electromagnetic waves. This formula relates the free space path loss, gained antenna, transmit and received powers wavelength.

# Friis Transmission Formula

#### Formula:

P_{r} / P_{t} = G_{r} G_{t} (λ / 4 π r) ^{2}

**Where,**

P_{r} = Input of the receiving antenna

P_{t} = Output power to the transmitting antenna

r = Distance between the antennas

λ = Wave Length

G = Antenna Gain

Friis Transmission formula is one of the fundamental equations in Antenna Theory. This Friis equation is essential for the analysis and design of wireless communication systems, since it is based on the gained antenna.