THE HAYSTACK-OBSERVATORY LAMBDA-3-MM UPGRADE

In this paper we describe a program to upgrade the Haystack 37-m radio telescope for operations at lambda3 mm. Attainment of useable antenna efficiency at these relatively short wavelengths (Haystack was originally designed for use at lambda3 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 active thermal control of a crucial element of the antenna structure-the splice plate, a heavy aluminum ring that 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, nonhomologous, 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 deformable subreflector was developed to correct phase errors arising on the antenna as a result of astigmatism and ring distortions. 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 mK Jy-1 is the highest of any lambda3-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.