A sensitive ALMA Band 10 SIS receiver engineering model

We have developed a single polarization engineering model of the Atacama Large Millimeter/Submillimeter Array (ALMA) Band 10 (0.78–0.95 THz) receivers. The front-end optics comprises a pair of ellipsoidal mirrors and a corrugated feed horn. A waveguide mixer block is attached to the feed horn in which an NbTiN-based superconductor–insulator–superconductor (SIS) mixer chip, which uses a quartz substrate, is mounted onto a WR-1.2 full-height waveguide. The SIS mixer employs two Nb / AlO x / Nb junctions and an NbTiN/SiO 2 /Al microstrip tuning circuit. A very wide intermediate frequency (IF) system with a bandwidth of 4–12 GHz is employed. The receiver demonstrated double-sideband (DSB) noise temperatures of below 240 K at local oscillator (LO) frequencies ranging from 792 to 945 GHz, without any correction for loss in front of the receiver. The lowest DSB receiver noise temperature, 179 K, was obtained at the center frequency of the designed band, which corresponds to about 4 quanta. These results represent state-of-the-art sensitivity for a receiver at an operating physical temperature of 4 K.