Optimisation of efficiency of reflector antennas: approximate method

A brief discussion of the theoretical approach to the problem of obtaining the maximum efficiency, for both paraboloidal- and spherical-reflector antennas, is presented. In both types of antenna, the problem reduces to obtaining the optimum combination of amplitude and phase of the hybrid modes propagating in the guide, so that, at the feed aperture, the resultant hybrid field closely matches that field which would be produced by a plane wave incident on the antenna. With shallow reflectors, a purely analytical method can be used, whereas graphical computer-aided optimisation techniques may be used to obtain the solution when the reflector is deep. The paper, however, presents a simple method of obtaining the approximate mode composition, which often proves to be satisfactory. As an illustration, results obtained by the approximate method are also compared with published results.