Dielectric Spherical Antenna Excited by a Cylindrical Currugated Waveguide

The radiation characteristics of a homogeneous dielectric sphere illuminated by a corrugated cylindrical waveguide with quarter wave teeth, carrying the hybrid mode (HE11) are studied. The field distribution at the aperture of the corrugated pipe is used as the sphere-illuminating source and the dielectric sphere is placed in front of, but displaced from this aperture. It is shown that this feed system has a near-circular far-field characteristics with increased on-axis gain. The feed also has 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.