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 origin ally designed for use at lambda3 cm) required, in addition to extensiv e and careful resetting of the surface panels, two critical developmen ts for control or correction of surface distortions. One is a system f or active thermal control of a crucial element of the antenna structur e-the splice plate, a heavy aluminum ring that serves to join the inne r 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, nonhomo logous, antenna design, which led to astigmatic and ring-like deformat ions with elevation angle. Part of the ring distortions can be correct ed by the active thermal-control system, but one full ring and part of another do not respond to thermal control. A novel deformable subrefl ector was developed to correct phase errors arising on the antenna as a result of astigmatism and ring distortions. Haystack is now fully op erational across the 86-115 GHz frequency range, with a nearly diffrac tion-limited primary beam (20'' at 115 GHz), and moderate efficiency-1 3% aperture and 18% beam efficiency at 115 GHz. The current 115 GHz se nsitivity of 50 mK Jy-1 is the highest of any lambda3-mm antenna in th e U.S. The highest sidelobes are below -15 dB. A sensitive, two-channe l 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.