  We developed a waveguide-type dual-polarization sideband-separating SIS
receiver system of the 100-GHz band for the 45-m radio telescope at the
Nobeyama Radio Observatory, Japan. This receiver is composed of an ortho-mode
transducer and two sideband-separating SIS mixers, which are both based on the
waveguide technique. The receiver has four intermediate frequency bands of
4.0--8.0 GHz. Over the radio frequency range of 80--120 GHz, the
single-sideband receiver noise temperatures are 50--100 K and the image
rejection ratios are greater than 10 dB. We developed new matching optics for
the telescope beam as well as new IF chains for the four IF signals. The new
receiver system was installed in the telescope, and we successfully observed
the 12CO, 13CO and C18O emission lines simultaneously toward the Sagittarius B2
region to confirm the performance of the receiver system. The SSB noise
temperature of the system, including the atmosphere, became approximately half
of that of the previous receiver system. The Image Rejection Ratios (IRRs) of
the two 2SB mixers were calculated from the 12CO and HCO+ spectra from the W51
giant molecular cloud, resulting in > 20 dB for one polarization and > 12 dB
for the other polarization.
