Antenna is a kind of transducer, which transforms the guided wave propagating on the transmission line into electromagnetic wave propagating in unbounded medium (usually free space), or vice versa. An antenna is a component used to transmit or receive electromagnetic waves in radio equipment. Engineering systems such as radio communication, broadcasting, television, radar, navigation, electronic countermeasures, remote sensing, radio astronomy, etc., which use electromagnetic waves to transmit information, all rely on antennas to work. In addition, in transmitting energy by electromagnetic waves, non-signal energy radiation also needs antennas. Generally, antennas are reversible, that is, the same antenna can be used as both transmitting antenna and receiving antenna.  

Communication, radar, navigation, broadcasting, television and other radio equipment all transmit information through radio waves, and they all need to be radiated and received by radio waves. In radio equipment, the device used to radiate and receive radio waves is called an antenna. The antenna provides the required coupling between the transmitter or receiver and the medium that propagates radio waves. Antenna, like transmitter and receiver, is also an important part of radio equipment.