Development of a dual-reflector feed for the radiotelescope in Arecibo. An overview

The spherical reflector antenna of the Arecibo Observatory will be equipped with a dual-reflector feed. This is often referred to as the Gregorian due to the Gregorian shapes of the two reflectors. The Gregorian has larger bandwidth, lower losses and provides better aperture distribution than the old line feeds. The authors describe the main ideas and review the methods and algorithms that have been developed to synthesize the shapes of the two reflectors, and to analyze them. Results are given of analysis by forward ray tracing using geometrical optics with included edge diffraction corrections. At low frequencies, analysis by physical optics integration is performed. Finally, the authors describe a `Mini-Gregorian´ that has been constructed, built and tested to verify the dual-reflector feed concept