What is the antenna

Antenna is a kind of converter, which transforms the guided wave propagating on the transmission line into the electromagnetic wave propagating in the unbounded medium (usually free space), or vice versa. In radio equipment, a component used to transmit or receive electromagnetic waves. Engineering systems such as radio communication, broadcasting, television, radar, navigation, electronic countermeasures, remote sensing, radio astronomy, etc., which use electromagnetic waves to transmit information, rely on antennas for work. In addition, in terms of transmitting energy with electromagnetic waves, non signal energy radiation also requires antennas. General antennas are reversible, that is, the same pair of antennas can be used as both transmitting and receiving antennas. The basic characteristic parameters of the same antenna as transmitting or receiving are the same. This is the reciprocity theorem of antennas.