Design of multimode shaped reflector antennas

Communication and broadcast satellites commonly employ contoured beam antennas to achieve efficient coverage of irregularly shaped geographical service areas. The use of shaped reflector antennas in generating a contoured beam is presently the preferred solution. A single corrugated horn is used to illuminate an offset reflector whose shape is designed to approximate the required radiation pattern. The paper describes a synthesis method for multimode shaped-reflector antennas that is based on physical optics calculations and simultaneously allows the synthesis of the reflector surface, the feed array and the multimode beam forming network (BFN). The application of this method to the next generation of European telecommunication missions (EUTELSAT III), demonstrates that, by using arrays with few radiating elements, this antenna configuration combines the structure simplicity and the electrical performance of a single beam shaped-reflector antenna with the capability of generating two or more simultaneous overlapped contoured beams without significant performance degradations. >