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