SYNTHESIS AND ANALYSIS OF A DUAL-REFLECTOR FEED FOR THE RADIOTELESCOPE IN NANCAY

The synthesis and analysis of a dual-reflector feed (DRF) for the radi otelescope in Nancay is presented. The telescope has an elongated sphe rical main reflector. The synthesis is done by geometrical optics (GO) based on the methods developed for the Gregorian feed of the radiotel escope in Arecibo. The DRF is diffraction-controlled in the vertical p lane. Still, GO synthesis is possible by replacing the spherical refle ctor by an auxiliary one with an empirically determined shape in the v ertical plane. The analysis is done by physical optics (PO) integratio n with the actual spherical primary reflector present. The results sho w that it is possible to correct for the spherical aberrations in the horizontal plane and to obtain a narrow diffraction-controlled beam in the vertical plane, as intended. The design is based on using corruga ted sector horns as feeds. They provide high aperture efficiency of th e telescope over the frequency band between 1-4 GHz. The sector horns have the same inner dimensions (height 28 cm, width 48 cm and length 3 0 cm), but the wall thicknesses are different due to the different cor rugation depths.