A monopulse Cassegrainian antenna

The diversity, simple configuration, and mechanical and electrical advantages of the Cassegrainian antenna have made it increasingly popular as a microwave director for radar systems. In detailed analysis of this type of antenna considered for use with a precise monopulse tracking radar, unique electrical characteristics are evidenced. These characteristics must be taken into account in the system design to insure optimum monopulse performance. The space-attenuation and monopulse- sensitivity functions are developed, and the special feed-to-subreflector near-field problem is explored with a discussion of proved solutions. Periodic design comparisons are made between the opaque-subreflector-type Cassegrainian antenna and the focal-point-feed antenna system where the single aperture, be it reflector or lens, is illuminated by a feed situated at the focal point. There is an often-used technique to circumvent the inherent aperture blocking introduced by the opaque subreflector, but it is mechanically complex and is costly. The performance limitations of the mechanically simpler opaque-subreflector-type Cassegrainian must be evaluated by the design engineer before going into these costly techniques.