A Broadband Low-Profile Monopulse Comparator for Dual-Circularly Polarized Feeder

This article proposes a scheme to design a broadband low-profile monopulse comparator for the dual-circularly polarized feeder. For obtaining a compact and easily integrated structure, a monopulse comparator with a ring-shaped symmetrical planner topology is proposed by using the 3 dB coupler and the phase shifter based on the groove gap waveguide (GGW). Then, in order to achieve the equal-amplitude distribution in a broad bandwidth, the asymmetrical coupling structure and the novel dispersion-matched transition are proposed to improve the directivity of a 3 dB coupler. Moreover, a ridge waveguide with periodic grooves featuring stable dispersion change is adopted to design the phase shifter, which contributes to obtain an accurate phase control in the broad frequency band. To validate experimentally the broadband performance, a dual-circularly polarized four-horn feeder with two identical monopulse comparators is designed and fabricated. The results show that the symmetrical radiation patterns with 32 dB null-depth can be obtained from 27 to 31 GHz. The monopulse comparator characterizes broad bandwidth, low loss, and a compact size, which provides a monopulse comparator with accurate amplitude/phase control for the research of the monopulse antenna.