What is Antenna Efficiency?

Antenna Efficiency is the ratio of power radiated (Prad) by the antenna to the power supplied (Ps) to the antenna. The efficiency of an antenna is usually measured in an anechoic chamber where an antenna is fed with some power and the strength of the radiated electromagnetic field in the surrounding space is measured.

An ideal antenna has 100% antenna efficiency i.e., it transmits all the power fed to it. But in the real world, a good antenna radiates only 50 to 60% of power supplied to it.