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We have developed a wideband receiver system for simultaneous observations inCO lines of J = 2-1 and J = 3-2 transitions using the Osaka 1.85-m mm-submmtelescope. As a frequency separation system, we developed multiplexers thatconnect three types of diplexers, each consisting of branch-line couplers andhigh-pass filters. The radio frequency (RF) signal is eventually distributedinto four frequency bands, each of which is fed to asuperconductor-insulator-superconductor (SIS) mixer. The RF signal from thehorn is divided into two frequency bands by a wideband diplexer with afractional bandwidth of 56%, and then each frequency band is further dividedinto two bands by each diplexer. The developed multiplexers were designed,fabricated, and characterized using a vector network analyzer. The measurementresults showed good agreement with the simulation. The receiver noisetemperature was measured by connecting the SIS-mixers, one of which has awideband 4-21GHz intermediate frequency (IF) output. The receiver noisetemperatures were measured to be ~70K in the 220GHz band, ~100K in the 230GHzband, 110-175K in the 330GHz band, and 150-250K in the 345GHz band. Thisreceiver system has been installed on the 1.85-m telescope at the NobeyamaRadio Observatory. We succeeded in the simultaneous observations of six COisotopologue lines with the transitions of J = 2-1 and J = 3-2 toward the OrionKL as well as the on-the-fly (OTF) mappings toward the Orion KL and W 51.

publications of the astronomical society of japan

Development of a new wideband heterodyne receiver system for the Osaka  1.85-m mm-submm telescope -- Receiver development & the first light of  simultaneous observation in 230GHz and 345GHz bands with an SIS-mixer with  4-21GHz IF output