An antenna is an arrangement of one or more conductors, which are called elements. During transmission, an alternating current (AC) is created in the elements by applying a voltage at the antenna terminals. This then causes the elements to radiate an electromagnetic field. During reception the received electromagnetic field induces an alternating current in the elements and a corresponding voltage at the antenna's terminals. The antenna, also know as an aerial, is the part of the system that transmits or receives these electromagnetic waves. On receive the antenna converts the electromagnetic radiation into electrical current and on transmit the antenna converts the electrical current into electromagnetic radiation. The antenna generally deals in the transmission and reception of radio waves, and is a necessary part of all radio equipment.

To sum it up, an ideal antenna is one that will radiate all the power delivered to it from the transmitter in a desired direction or directions. However, in practice such performances cannot be achieved but may be closely approached.

Some of the first antennas were built in 1888 by Heinrich Hertz (1857–1894) in his pioneering experiments to prove the existence of electromagnetic waves predicted by the theory of James Clerk Maxwell. (Annalen der Physik und Chemie)