We have developed a low-noise submillimeter-wave SIS receiver (320-360 GHz) for a 10 m submillimeter telescope, which was installed at Nobeyama in 2000 February. This receiver and a millimeter-wave SIS receiver are mounted on the ceiling of the Cassegrain receiver cabin of the 10 m telescope. Two curved mirrors couple a shaped Cassegrain beam from the subreflector to mixer horns. The minimum noise temperature measured in front of the receiver was 52 K in double sideband (DSB) at a local oscillator (LO) frequency of 354 GHz, which corresponds to three-times quantum limits (3hv/kB). This noise temperature contributions are resolved into the optics, mixer, and IF parts. The temperature ripple of a two-stage Gifford-McMahon cryocooler has been reduced to be 2 mK peak-to-peak at the mixer block with a helium pot temperature stabilizer. Mechanical vibration (30 μm peak-to-peak) of the cold head degrades the receiver stability.
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