Design and measurement of satellite reflector antennas with high coverage gain

The paper discusses some design considerations for pencil-beam antennas with maximum coverage gain to be used as broadcast satellite antennas with the requirement of uniform illumination of a terrestrial area. A formula obtained by the calculus of variations applied to the gain formula and giving the optimum aperture illumination functions for circular apertures is the basis of discussion. The optimum radiation characteristics were approximated in a center-fed and an offset-fed prime focus reflector, yielding 70.2 and 72 percent coverage efficiency, respectively. In a Cassegrain antenna, the real feed and the subreflector are replaced by the virtual feed at the focal point of the main reflector, so that the Cassegrain system is reduced to a single reflector system having the same main reflector but a different feed. It has been found that the Cassegrain-fed elliptic reflector with subreflector tilted about the focal point yields excellent scan performance but 10% lower coverage efficiency compared to the center-fed prime focus reflector.