Development of ALMA Band 4 (125–163 GHz) receiver

We have developed a dual-polarization receiver for Band 4 of the Atacama Large Millimeter/submillimeter Array (ALMA). Band 4, which covers the 125 to 163 GHz spectral window, is one of the ten bands that form the ALMA Front End. The Band 4 receiver consists of three elements: a warm optics, a cold cartridge assembly, and a warm cartridge assembly. The cold cartridge includes a feed horn, an orthomode transducer, sideband-separating (2SB) superconductor–insulator–superconductor mixers, cold intermediate frequency (IF) amplifiers, IF isolators, bias-protection circuit boards, and component interconnections. The IF bandwidth is 4–8 GHz. The first eight receivers manufactured as preproduction models have demonstrated excellent performance within the stringent ALMA requirements. Stable astronomical fringes and closure phase have been successfully achieved during field performance tests of the Band 4 receivers installed in the ALMA antennas. Our well-established Band 4 receivers will contribute to various fields of astronomical research, such as the detection of high-redshift galaxies, characterization of cold molecular medium in normal field galaxies, and astrochemistry including observations of deuterated species.