An Instrument for Investigation of the Cosmic Microwave Background Radiation at Intermediate Angular Scales

We describe an off-axis microwave telescope for observations of theanisotropy in the cosmic microwave background (CMB) radiation on angular scalesbetween 0.5 deg and 3 deg. The receiver utilizes cryogenichigh-electron-mobility transistor (HEMT) amplifiers and detects the total powerin multiple 3 GHz wide channels. Both frequency and polarization informationare recorded allowing discrimination between CMB radiation and potentialforeground sources and allowing checks for systematic effects. The instrumentalradiometric offset is small (~1 mK). Data are taken by rapidly sampling whilesweeping the beam many beamwidths across the sky. After detection, aspatio-temporal filter is formed in software which optimizes the sensitivity ina multipole band in the presence of atmospheric fluctuations. Observations weremade from Saskatoon, Saskatchewan (SK), Canada during the winter of 1993 withsix channels between 27.6 and 34.0 GHz, in 1994 with twelve channels between27.6 and 44.1 GHz, and in 1995 with six channels between 38.2 and 44.1 GHz. Theperformance of the instrument and assessment of the atmospheric noise at thissite are discussed.Comment: latex file is called inst.tex. 30 pages with 14 Postscript figures. Uses aas2pp4.sty (included). Submitted to Ap