High performance dual shaped reflector antennas for earth stations

Abstract

In satellite communications, the earth station antenna plays a major role in the vital link between the satellite and the earth station electronic equipment. In this thesis, dual shaped reflector antennas for earth stations which can provide a pencil beam toward a geostationary satellite are introduced. The design and analysis of both Cassegrain and Gregorian antennas are presented as follows. -- (i) The high performance antenna feeds are studied in detail. Various specific characteristics required in Cassegrain and Gregorian antennas are discussed and it is shown that the corrugated conical horn is the best choice. -- (ii) The computer aided synthesis of subreflector and main reflector are developed by using the geometric optics (GO) approach. Given the feed radiation pattern and the desired main reflector aperture power illumination, the sub and main reflectors can be shaped to obtain optimal reflector profiles. -- (iii) After having the sub and main reflector profiles, the physical optics (PO) are used to calculate the scattered pattern of the subreflector, the radiation patterns as well as the whole antenna specifications. -- (iv) A number of power distributions on the main reflector aperture are investigated to maximize the boresight gain and at the same time, minimize the sidelobe levels. A pattern control method is also developed. -- (v) Performance comparison between Cassegrain antenna and Gregorian antenna is also made. -- The major contribution of this thesis is the complete computer aided design tool for a very high performance antenna.