Computer-Aided Analysis of Cassegrain Antennas

The essential radiation characteristics of multiple reflector antennas can be predicted very accurately with existing analytical and computational methods. Previous work on the open Cassegrain antenna showed that good agreement can be achieved between calculated and experimental results. 1 Deviations occurred mainly in the sidelobe regions of the radiation patterns, and these had only a small effect on overall antenna performance. 897 898 T H E BELL SYSTEM TECHNICAL JOURNAL, JULY-AUC.UST 1908 We are concerned here with a simpler problem, but one of perhaps more general interest: the analysis of symmetrical Cassegrain antennas. We present a computational method in which the amplitude and phase illuminations of the subreflector and main-reflector, as well as the far-field radiation pattern, are determined in detail, given the geometry of the antenna, the dimensions of the feed horn, and the excitation modes of the feed. The analysis includes near-field excitation--an important configuration for broadband operation. Included in the program is a graphic routine which plots all radiation patterns, the intermediate illuminations and the final far-fielcl results. Because of the this feature, and the fact that only seven parameters are required to define the geometry of the antenna, the program is particularly useful for optimizing antenna performance. The symmetry of the antenna results in improved computational efficiency. For the open Cassegrain antenna, double-integration was required to compute radiation patterns.