Optimum coaxial cavity horn for high aperture efficiency and low cross-polarization

A coaxial cavity-feed horn has been analyzed using the geometrical theory of diffraction, and the radiation characteristics are investigated numerically. Surface integral equations are formulated, and the moment method is used to reduce the integral equation to a matrix equation. The copolar and cross-polar radiation patterns, as well as the aperture efficiency and phase center location, are computed. Good agreement between the computed and measured data is observed with very good symmetry between E- and H-plane patterns. This process results in a feed with a cross polarization level of -28.77 dB. It is believed that the high cross polarization level originally observed is due to the separation of the phase centers of the circular waveguide and the coaxial cavity, which caused a large separation between the phase center location of the E- and H-planes. Thus, the coaxial cavity depth has been modified to correct the phase center, and the coaxial cavity wall has been extended beyond the circular waveguide aperture to correct the H-plane amplitude pattern.<>