Dielectric sphere-loaded radial surface-wave antenna

Abstract

The results of an experimental and theoretical study of the radiation characteristics of a high-gain antenna feed system are reported. The feed system consists of a homogeneous dielectric sphere offset in front of the aperture of a radial surface-wave horn formed by a E-plane sectoral horn with its bottom plane having a layer of dielectric coating keeping the top plane truncated at a height where the field concentration is almost negligible. Firstly, the radiation characteristics with on-axis gain of the surface-wave E-plane sectoral horn alone are derived for TE₁₀ mode excitation, from an electric vector potential on the basis of the vector diffraction formula. Then the radiation characteristics of the feed system are derived by treating the system as a microwave lens illuminated by an aperture source. Theoretical results and established in good agreement with experimental results of radiation pattern and gain measurements. It is concluded that radial surface-wave horn antennas have on-axis gain in excess of that of conventional E-plane sectoral horns, and also that the radiation characteristics of the surface-wave horn are improved further with greater directivity, increased on-axis gain and reduced side.lobe levels (beyond 90°, the side lobo level is of negligible magnitude being leas than - 40 dB) due to the offset dielectric sphere at its aperture.