Study of diffraction blockage effects in the Arecibo dual-reflector feed using physical optics

The Arecibo Gregorian dual-reflector feed is a a very compact structure which has been designed using geometrical optics (GO). The feed geometry compensates for the spherical aberration inherent in an antenna system using a spherical main reflector. There has been concern that, at low frequencies, objects close to the GO ray paths might perturb the fields emanating from the feed, and consequently the aperture field of the spherical reflector, to such an extent that a significant deterioration of the resulting radiation patterns would ensue. The authors refer to such perturbations as diffraction blockage. They have calculated the fields at various locations inside the dual-reflector feed (DRF) using physical optics (PO) integration at 430 MHz, and made an assessment of the effects, due to blockage, on the overall performance. They have also included some of the effects of blockage in the PO analysis of the entire antenna system. By doing PO calculations via blocking objects in the DRF, the perturbations of the aperture fields and radiation patterns due to the presence of conducting bodies in the vicinity of the GO ray paths are computed.<>