Beam waveguide antennas are used in large
radio telescopes and
satellite communication stations as an alternative to the most common parabolic antenna design, the conventional "front fed" parabolic antenna. In front feed, the
antenna feed, the small
antenna that transmits or receives the radio waves reflected by the dish, is suspended at the
focus, in front of the dish. However, this location causes a number of practical difficulties. In high performance systems, complex transmitter and receiver electronics must be located at the feed antenna. This feed equipment usually requires high maintenance; some examples are
water cooling for transmitters and
cryogenic cooling for sensitive receivers. With the large dishes used in these systems, the focus is high off the ground, and servicing requires cranes or scaffolds, and outdoor work with delicate equipment high off the ground. Furthermore, the feeds themselves have to be designed to handle outdoor conditions such as rain and large temperature swings, and to work while tipped at any angle. The beam waveguide antenna addresses these problems by locating the feed antenna in a "feed house" at the base of the antenna, instead of in front of the dish. The radio waves collected by the dish are focused into a beam and reflected by metal surfaces in a path through the supporting structure to the stationary feed antenna at the base. The path is complicated because the beam must pass through both axes of the
altazimuth mount of the antenna, so turning the antenna does not disturb the beam. ==History==