Description
A horn antenna is used to transmit radio waves from a waveguide (a metal pipe used to carry radio waves) out into space, or collect radio waves into a waveguide for reception. It typically consists of a short length of rectangular or cylindrical metal tube (the waveguide), closed at one end, flaring into an open-ended conical or pyramidal shaped horn on the other end. The radio waves are usually introduced into the waveguide by a coaxial cable attached to the side, with the central conductor projecting into the waveguide to form a quarter-wave monopole antenna. The waves then radiate out the horn end in a narrow beam. However in some equipment the radio waves are conducted between the transmitter or receiver and the antenna by a waveguide, and in this case the horn is just attached to the end of the waveguide. In horns installed outdoors, such as the feed horns of satellite dishes, the open mouth of the horn is often covered by a plastic sheet which is transparent to the radio waves, to keep out moisture.
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