Pointing large antennas using the conical scan technique

Cornell University, NAIC, Arecibo Observatory, P.O. Box 995, Arecibo, Puerto Rico 00613, U.S.A.

Send offprint request to: M. Davis

Received: 13 May 1997
Accepted: 11 September 1997

Abstract

We describe an alternative way of pointing (large) radiotelescopes using a method derived from radar tracking techniques, and generally known as conical scanning. It can be accomplished by using either a feed that is mechanically (or electrically) displaced from the boresight axis, or by fixing the feed and translating or rotating a tilted subreflector. The optimum set–up for radioastronomical application depends upon the antenna configuration, the feed mount, and the sizes/weights of the moving parts involved. In the case of the new Gregorian configuration for the Arecibo telescope, the mechanical and electromagnetic configuration suggests the use of combined motions of the tertiary reflector in elevation and the feed turret in cross–elevation. We analyse several methods of implementing the conical scan technique and evaluate them through numerical simulations.