The Ultimate S-Band Monopulse Focal-Point Feed

A newly developed high-efficiency S-band tracking feed is described. It is a focal-point feed designed primarily for use with parabolic reflectors in the 15 to 25 foot diameter class. A five-element aperture geometry was developed to obtain improved performance in sum and difference pattern efficiency over that normally obtained with four-element, hybrid-comparator feeds. Two major e mprovements were obtained: a. Elimination of the conventional hybrid comparator resulted in the ??ultimate?? sum-channel efficiency, hence minimum noise temperature degradation due to feed losses. b. Independent control of the difference-pattern illumination produced ??near-optimum?? gainslope performance simultaneously with optimized sum-channel illumination. Design theory for this feed geometry is discussed, and measured impedance and radiation pattern data obtained from the finished feed system are presented.