Phased Array Feeds for Low Noise Reflector Antennas

Phased array feeds offer the possibility of more efficient use of large radio astronomy reflector antennas by providing more closely spaced beams over a wide field of view and higher aperture efficiency in each beam than have been realized with horn feeds. Phased arrays have been used extensively in rapid scanning radars and shaped-beam satellite systems, but the array design criteria for low-noise radio astronomy antennas are markedly different, particularly as they affect array sampling density. Element spacing in the focal plane must be less than lA for large FID reflectors and less than about 0.7A for FID < 0.5. This rules out conventional horns as array elements and imposes a limit on the array bandwidth. The receive-only case of radio astronomy permit the use of a number of signal combining techniques that do not degrade system sensitivity. Problems of array weight optimization, mutual coupling, and correction of reflector errors are examined briefly in this paper.