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 radiotelescope in Nancay is presented. The telescope has an elongated spherical main reflector. The synthesis is done by geometrical optics (GO) based on the methods developed for the Gregorian feed of the radiotelescope in Arecibo. The DRF is diffraction-controlled in the vertical plane. Still, GO synthesis is possible by replacing the spherical reflector by an auxiliary one with an empirically determined shape in the vertical plane. The analysis is done by physical optics (PO) integration with the actual spherical primary reflector present. The results show 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 corrugated sector horns as feeds. They provide high aperture efficiency of the 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 30 cm), but the wall thicknesses are different due to the different corrugation depths