A Multibeam, Spherical-Reflector Satellite Antenna for the 20- and 30-GHz Bands

A proposed domestic satellite system for the 20- and 30-GHz radio bands includes a multibeam satellite antenna. 1 The use of separate radiating beams to service specific densely populated urban areas is desirable since it permits reuse of the frequency bands and flexibility in traffic routing. A multibeam satellite antenna that operates simultaneously in the 20- and 30-GHz bands has been constructed and evaluated electrically. The antenna is a compact periscope design2 employing a spherical reflector 60 inches in diameter, a plane reflector, and a cluster of six feed horns. Figure 1 shows two views of the antenna system. A spherical rather than a parabolic reflector was employed to permit off-axis beam pointing with less degradation in performance than a paraboloid. The primary feature of this antenna design is the use of multiple feeds to produce separate radiation beams. The feed location format was chosen to conform with earth-station locations at approximately New York City, Denver, Atlanta, Los Angeles, Honolulu, and Puerto Rico. These locations are representative of the maximum beam-pointing requirement for domestic satellite service and the minimum beam-pointing constraint owing to physical feed separation. The synchronous orbiting satellite was assumed to be located at 100 degrees west longitude. The antenna system boresight axis that corresponds to the axis of symmetry of the spherical reflector is designed to intersect the earth at 38 degrees north latitude and 100 degrees west longitude, near the geo1011