THE HAYSTACK OBSERVATORY LAMBDA-3-MM UPGRADE

Abstract

ABSTRACT In this paper we describe a program to upgrade the Haystack 37-m radio telescope for operations at lambda-3-mm. Attainment of useable antenna efficiency at these relatively short wavelengths (Haystack was originally designed for use at lambda-3-cm) required, in addition to extensive and careful resetting of the surface panels, two critical developments for control or correction of surface distortions. One is a system for ative thermal control of a crucial element of the antenna structure--the splice plate, a heavy aluminum ring which serves to join the inner and outer antenna panels. Thermal lags in this ring relative to the panels previously caused high amplitude, ring-like deformations on the surface. The other development was necessitated by the early, non-homologous, antenna design, which led to astigmatic and ring-like deformations with elevation angle. Part of the ring distortions can be corrected by the active thermal-control system, but one full ring and part of another do not respond to thermal control. A novel deformation sureflector was developed to correct phase errors arising on the antenna as a result of astigmatism and ring distortion. Haystack is now fully operational across the 86-115 GHz frequency range, with a nearly diffraction-limited primary beam (20" at 115 GHz), and moderate efficiency--13% aperture and 18% beam efficiency at 115 GHz. The current 115 GHz sensitivity of 50 mJy/K is the highest of any lambda-3 mm antenna in the U.S. The highest sidelobes are below -15 dB. A sensitive, two-channel SIS mixer radiometer has been developed, with system temperatures of 200-400 K (depending on frequency) under dry conditions, followed by a flexible new autocorrelation spectrometer with 4096 lags and 160-MHz bandwidth.