DEVELOPMENTS OF THE 810-GHz SIS RECEIVER WITH Nb-BASED JUNCTIONS

We present the experimental and astronomical results of the tunerless waveguide 810GHz SIS receiver. The Nb/AlOx/Nb junctions associated with a broadband tuning circuit, namely parallel connected twin junctions, are fabricated at Nobeyama Radio Observatory. The tuning microstrip line is made of a Nb thin lm. The lowest receiver noise temperature is 580 K (DSB) measured at 810 GHz, in which the noise contributions of the RF-input section alone and the IF-system account for about 4 % and 20 %, respectively. Note that the applied magnetic eld with a permanent magnet to suppress the Josephson e ect is 700 800 Gauss and the SIS mixer is cooled down to 3.9 K. The R sub (2mV)/R N is 16, which suggests relatively good quality of the junctions. This SIS mixer was installed on the receiver of the Mount Fuji submillimeter-wave telescope. We have detected the submillimeter-wave spectral lines of CI (3P23P1 : 809.3432 GHz) and CO (J=7-6 : 806.651 GHz) in the Orion A molecular cloud.