Mode matching analysis of small Cassegrainian reflector antennas

It is shown that a combined circular and cylindrical mode matching techniques previously developed for the analysis of frequency diplexing structures (see S.M. Tun, International Conference on Computation in Electromagnetics, London, UK, IEE Conf. no.350, p.230-3, 1991) can be used to model compact Cassegrainian reflector antennas with aperture diameters less than 20 wavelengths. Such small antennas are difficult to design due to the presence of multiple interactions between the feed, subreflector and the main reflector. The analysis method is capable of taking into account all these interactions by representing the two reflectors and the feed as a series of cylindrical waveguide segments. Dielectric supports and lens structures can also be incorporated in the analysis. The analysis software has been successfully used to design a small splash plate feed antenna with low sidelobes. Although the mode matching method is not as flexible as those based on methods of moments, the authors illustrate that it can be used to predict radiation performance of small reflector antennas in the forward direction