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An antenna element can be any part of an antenna involved in the reception or transmission of a signal. Properly speaking, an antenna element is any part of an antenna active in the reception or transmission of signals. This is in contrast to other components that affect the reception and transmission capabilities of an antenna but do so passively. Examples of antenna elements include metal rod on a rabbit-ear type television antenna or the wire loop of a UHF television antenna.
A proper antenna element acts as a transducer. A transducer is a device that converts energy from one form to another. In an antenna element, this can work in one of two different but related ways. First, the element can convert electrical energy to radio frequency energy, which is what occurs when transmitting a signal through an antenna. Second, the element can convert radio frequency energy to electrical energy, which is what occurs when a signal is received through an antenna.
When an antenna element transmits a radio signal, the desired signal is applied to the element in the form of an electrical AC signal. The AC signal causes the element to resonate at a particular frequency, which in turn generates an electromagnetic field directly proportional to the applied AC signal that expands in the direction, or directions, determined by the antenna element’s physical design. Antenna elements typically transmit in either a single direction, allowing the signal to be received in a fairly small area, but at a relatively high power level, or in all directions, covering a large area but at a relatively low power level.
While receiving signals, an antenna element works essentially in the reverse order of a transmitting element. An electromagnetic field created by a transmitting antenna causes the receiving element to resonate. As the element resonates, it generates an electrical AC signal directly proportional to the electromagnetic field. Like transmitting elements, receiving elements can be designed to receive signals from all directions but at a relatively low power level or from a single direction at a relatively high power level.
Some antennas have additional components considered by some to be antenna elements because they contribute to the antenna’s performance in some way. Usually, these additional elements take the form of a reflector or director. Reflectors typically bounce a signal back toward the active element that has already passed it. Directors bounce signals toward the active element before they would otherwise pass it. An example of a reflector would be the parabolic dish used with satellite antennas, while an example of a director would be the many metal tubes seen on rooftop TV antennas.