Antenna: a transducer designed to transmit or to receive radio waves (electromagnetic waves). An antenna converts radio frequency electrical currents into electromagnetic waves and vice versa.

An attena is a conductor designed to translate an alternating current from an electromagnetic field or to translate an electromagnetic field from an alernating current. An antenna "transmits" when it radiates an electromagnetic field in response to an applied alternating current. An antenna "receives" when it induces an alternating current in response to an ambient electromagnetic field.

An antenna that transmits most effectively in a certain direction will also receive signals most effectively from the same direction.

RFID readers (interrogators) have antennas and RFID tags have antennas.

In RFID applications, antennas consist of two general types. Inductive antennas are coils that use magnetic coupling; they are most commonly encountered in low-frequency and high-frequency tags and readers, but are also used in ultra-high-frequency near-field tags. Most UHF and microwave tags use variants of the dipole antenna, and are radiatively coupled to the reader antenna, which is often a patch antenna or (less frequently) a Yagi-Uda type antenna.

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