An antenna is a kind of electrical device which converts electric power into radio waves, and vice versa. It is usually used with a radio transmitter， phone or some other radio receiver. In transmission, a radio transmitter supplies an oscillating radio frequency electric current to the antenna's terminals, and the antenna radiates the energy from the current as radio waves (electromagnetic waves: EW). In reception, an antenna intercepts some of the power of an EW in order to produce a tiny voltage at its terminals, that is applied to a receiver to be amplified.