Comparison between multifeed and shaped reflector satellite antennasfor contoured beams

Abstract

Performance requirements placed on satellite communications antennas are becoming increasingly stringent; complex requirements such as multiple contiguous spot and complex contoured beams are becoming the rule rather than the exception for designers of satellite antennas. In the first case, multiple spot beam requirements have driven the development of reflector antennas towards imaging array and matrix-fed focusing architectures. In the case of contoured beam antennas, competing technologies are paraboloids fed by horn arrays, and shaped reflector antennas fed by one or a few high performance feeds. Where the specification demands dual-linear polarisation, the cross-polar requirement will necessitate the use of gridded reflectors in the array-fed case, and dual reflector systems satisfying the Mitzuguchi low-crosspolar condition in the shaped reflector case. British Aerospace has been active in both areas of antenna architecture, and is at the forefront of developments in the dual shaped reflector antenna field, both in the development of synthesis algorithms and in hardware, having been awarded a contract by the European Space Agency in 1988 for the design and manufacture to EM standard of a dual shaped reflector antenna for contoured beam coverage of Europe. Over the last few years, therefore, a considerable body of data has been accumulated, comprising design and performance information from many antennas of both multifeed and shaped reflector types. In some cases, designs of both types have been carried out for the same or similar coverage requirements. enabling conclusions to be drawn as to the relative performance of the two types.