Radiation characteristics of a dielectric sphere-loaded corrugated pipe

The fields radiated by a feed structure consisting of a dielectric sphere placed in front of, but displaced from, the open end of a corrugated pipe with quarter-wave teeth, carrying the HE11mode, are derived. It is shown that this feed system has near-circular far-field characteristics with increased on-axis gain. The feed also has a reduced input VSWR due to the aperture-sphere separation. Theoretical expressions are derived for the radiated far-field components, by treating the off-set sphere as a microwave lens. Experimental results obtained from a test feed confirm the theoretical calculations made.