Multi-feed Systems for the Arecibo Gregorian

The 305-m diameter spherical reflector antenna in Arecibo, Puerto Rico, is the largest filled-aperture radio telescope in the world. The Gregorian subreflector system is being developed to correct the spherical aberration of the primary, and thus replace the line feeds which have been used until the present time. The two-reflector optical system will allow continuous frequency coverage at frequencies up to ~ 10 GHz, as well as offering increased sensitivity and lower system temperatures resulting from reduced spillover. In addition, a limited imaging capability will be available, offering the possibility of moderate-sized focal plane arrays for surveys and study of extended sources. Theoretical calculations of imaging performance for several arrays in the frequency range of 1.4 to 10 GHz have been carried out. Reasonable numbers of elements vary from 7 at 1.4 GHz to 14 at 10 GHz. A 1024-lag correlator chip developed by J. Hagen (NAIC) and J. Canaris (U. New Mexico/NASA SERC) will form the basis of an array spectrometer system for galactic and extragalactic spectroscopy.