A New Monopulse Feed System for Increased Tracking Accuracy of Radars

This paper describes a new monopulse feed system that enhances the tracking accuracy and operating bandwidth of a space-fed radar. The feed comprises a compact 'mode triplexer' and a multimode corrugated horn. Signal strength of the two higher order modes with respect to the dominant mode at the triplexer output ports furnishes an estimation of angular co-ordinates in azimuth and elevation planes. Efficient microwave networking in the mode triplexer improves the operating bandwidth. The horn launches multiple higher order modes to optimize the feed aperture field distribution, simultaneously, for the Σ and Δ beams. Beam dependent effective size of the aperture in the multimode horn enhances the tracking accuracy of the radar. Based on measured data, a net 70% improvement of tracking accuracy and 6 dB improvement of difference beam sidelobes are achieved over a 7% bandwidth in a space-fed radar retrofitted with the new feed system.