 - An antenna is a specialized transducer that converts radio-frequency (RF) fields into alternating current (AC) or vice-versa. There are two basic types: the receiving antenna, which intercepts RF energy and delivers AC to electronic equipment, and the transmitting antenna, which is fed with AC from electronic equipment and generates an RF field.In computer and Internet wirelessapplications, the most common type of antenna is the dish antenna, usedfor satellite communications.Dish antennas are generally practical only at microwave frequencies (above approximately 3 GHz). The dish consists of a paraboloidal or sphericalreflector with an active element at its focus. When used forreceiving, the dishcollects RF from a distant source and focuses it at the activeelement.When usedfor transmitting, the active element radiates RF that is collimated by thereflector fordelivery in a specific direction. At frequencies below 3 GHz, many different types ofantennas are used. The simplest is a length of wire, connected at one end to atransmitter or receiver. More often, the radiating/receiving element is placed at adistance from the transmitter or receiver, and AC is delivered to or from the antenna bymeans of an RF transmission line, also called a feed line orfeeder.
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11 Apr 2003
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