Sideband-separating MMIC receivers for observation in the 3-mm band

Wideband receivers for the 3-mm band were developed for CARMA, the Combined Array for Research in Millimeter wave Astronomy. Three cryogenic MMIC (monolithic microwave integrated circuit) amplifiers manufactured in InP 35-nm technology are combined in a block with waveguide probes and gain equalizers to cover the 80-116 GHz band. These are followed by a sideband-separating mixer that has two 17 GHZ wide outputs, for upper and lower sidebands. Each receiver has a feed horn followed by a circular-to-linear polarizer and orthomode transducer. The two polarizations are amplified by the cryogenic MMICs, and the outputs downconverted in sideband separating mixers, resulting in four 1-18 GHz channels that can be simultaneously correlated. The first receiver was tested in the lab, and on-sky tests conducted at CARMA. Measured noise temperatures were in the range 40-70 K, with a sideband rejection of about 15 dB.