What is Free Space Path Loss?

The free space path loss of an antenna is the reduction of the power of the signal traveling in free space, vacuum, or any obstacle hindering its propagation. FSPL is used to help predict RF signal strength in an antenna system. It is an important parameter to be considered in the power link estimation of a radio communication system.

The Free Space Loss is expressed as:

FSPL = 20 log₁₀(d) + 20 log₁₀(f) + 20 log10  – G_t – G_r

Where

D is the distance between the transmitter and the receiver

f is the frequency

G_t is the gain of the transmitting antenna 

Gr is the gain of the receiving antenna