A 650-GHz band SIS receiver for balloon-borne limb-emission sounder

A superconducting few-noise receiver has been developed for atmospheric obs ervations in the 650-GHz band. A waveguide-type tunerless mixer mount was d esigned based on one for the 200-GHz band. Two niobium SIS (superconductor- insulator-superconductor) junctions were connected by a tuning inductance t o cancel the junction capacitance. We designed the omega RnCj product to be 8 and the current density to be 5.5 kA/cm(2). The measured receiver noise temperature in DSB was 126-259 K in the frequency range of 618-660 GHz at a n IF of 5.2 GHz, and that in the IF band (5-7 GHz) was 126-167 K at 621 GHz . Direct detection measurements using a Fourier transform spectrometer (FTS ) showed the frequency response of the SIS mixer to be in the range of abou t 500-700 GHz. The fractional bandwidth was about 14%. The SIS receiver wil l be installed in a balloon-borne limb-emission sounder that will be launch ed from Sanriku Balloon Center in Japan.