A dual-reflector feed for the radio telescope in Nancay synthesised by geometrical optics

The Nancay telescope is a transit telescope of the Kraus type, consisting of a fixed spherical reflector (referred to as the primary reflector) and a tiltable flat reflector. The spherical reflector has a vertical aperture that is D/sub x/=34.6 m high and D/sub y/=200 m wide, and the paraxial focus is located on the ground F=279.9 m in front of the centre of the primary. The tiltable flat reflector is located about 560 m in front of the primary, and the purpose of it is to redirect the horizontal beam from the sphere towards a desired elevation direction on the sky. The existing feeds for the primary are so-called hoghorns. The purpose of the paper is to present a dual-reflector feed (DRF) for the Nancay telescope. This DRF is designed to illuminate the sphere under the required angles of /spl theta//sub x/=arctan(D/sub x//F)=7 deg and /spl theta//sub y/=2arctan(D/sub y//2F)=40 deg in the vertical and horizontal planes, respectively. The DRF is designed to correct for the spherical aberrations in the horizontal plane (wide beam) by means of geometrical optics (GO), and to provide as narrow beam as possible compared to its size in the elevation plane by making use of aperture diffraction. The DRF is designed to work between 1 GHz and 3.3 GHz by using different feed horns.<>