Analysis Of Electrically Small Hyperbolic Subreflectors Utilizing The Geometrical Theory Of Diffraction

Cassegrain antennas have been utilized in applications where small size is critical. It has been observed that for antennas having subreflectors of the order of only several λ in diameter, near-in sidelobe levels rise beyond normally predicted values. E- plane sidelobes axe often several dB higher than those in the Η-plane. Disturbances in the illumination of the primary reflector due to diffraction limitations of the electrically small subreflector axe a possible cause of the sidelobe phenomenon. In this work, the results for 3 to 8 λ -diameter hyperboloidal subreflectors, using the geometrical theory of diffraction (GTD) are presented and compared with the physical optics approach and other data. Degradation of the scatter patterns are observed as the subreflector size is decreased, and the differences in the E-and Η-plane phase and amplitude patterns are observed in the GTD solution.© 1993, VSP. All rights reserved