A Bolometric Millimeter-Wave System for Observations of Anisotropy in the Cosmic Microwave Background Radiation on Medium Angular Scales

We report the performance of a bolometric system designed to measure the anisotropy of the cosmic microwave background (CMB) radiation on angular scales from 0.3^deg^ to 3^deg^, The system represents a collaborative effort combining a low-background 1 m diameter balloon- borne telescope with new multimode feed optics, a beam modulation mechanism with high stability, and a four channel bolometric receiver with passbands centered near frequencies of 3(90), 6(180), 9(270), and 12(360) cm^-1^(GHz). The telescope has been flown three times with the bolometric receiver and has demonstrated detector noise limited performance capable of reaching sensitivity levels of {DELTA}T/T_CMB_~ 10^-5^ with detectors operated at T = 0.3 K.