Hybrid-Mode, Shielded, Offset Parabolic Antenna

Hybrid-Mode, Shielded, Offset Parabolic Antenna By R. A. SEMPLAK (Manuscript received September 24, 1981) In this paper measurements are presented for both a hybrid-mode feed having corrugations in two opposite walls and a modified scalemodel pyramidal horn-reflector antenna using this feed. Comparisons of the measured and theoretical data for the hybrid-mode shielded offset parabolic antenna with the theoretical data for the standard pyramidal horn-reflector antenna show that a net improvement can be obtained in sidelobe level of about 4 dB in the transverse polarization in the transverse plane and 4 to 13 dB in the longitudinal polarization in the longitudinal plane. I. INTRODUCTION In most respects, the standard pyramidal horn-reflector is an excellent antenna. It is a combination of a square pyramidal horn and a reflector that is a section of a paraboloid of revolution whose focus coincides with the apex of the square horn. Its geometry provides a shielded offset parabolic antenna that is broadband with good frontto-back discrimination and good return loss. However, inherent in the design of the pyramidal horn-reflector antenna is a problem that results from illuminating the reflector with a dominant waveguide mode.1 The theoretically obtainable off-axis radiation levels for transverse polarization in the transverse plane and longitudinal polarization in the longitudinal plane are considerably higher than those obtained for longitudinal polarization in the transverse plane and transverse polarization in the longitudinal plane, i.e., the former are essentially the equivalent of an aperture with constant illumination, whereas the latter aperture field distributions are tapered to zero at the edges.