Compact low cross-polarization multimode horn with ring-loaded coaxial grooves

Coaxial feeds are effective to obtain rotationally symmetrical radiation patterns with a broad beamwidth or primary patterns reducing the spillover loss. For precisely controlling mutual coupling between the fed waveguide and the outer corrugation, we have developed a multimode horn loading coaxial grooves which works as a higher-order mode converter. In this paper, for improving the frequency characteristics of a low cross-polarization multimode horn, we propose a horn consisting of ring-loaded coaxial grooves with different dimensions each other, unlike the previously proposed horns. As a design example, we present a compact horn illuminating a circular area of angular diameter 40° with 30%-bandwidth in X-band.