We have developed a two-beam waveguide-type dual-polarization sideband-separating SIS receiver system in the 100-GHz band for z -machine on the 45-m radio telescope at the Nobeyama Radio Observatory .
The receiver is intended for astronomical use in searching for highly redshifted spectral lines from galaxies of unknown redshift .
This receiver has two beams , which have 45 ^ { \prime \prime } of beam separation and allow for observation with the switch in the on-on position .
The receiver of each beam is composed of an ortho-mode transducer and two sideband-separating SIS mixers , which are both based on a waveguide technique , and the receiver has four intermediate frequency bands of 4.0–8.0 GHz .
Over the radio frequency range of 80–116 GHz , the single-sideband receiver noise temperature is lower than about 50 K , and the image rejection ratios are greater than 10 dB in most of the same frequency range .
The new receiver system has been installed in the telescope , and we successfully observed a ^ { 12 } CO ( J =3–2 ) emission line toward a cloverleaf quasar at z = 2.56 , which validates the performance of the receiver system .
The SSB noise temperature of the system , including the atmosphere , is typically 150–300 K at a radio frequency of 97 GHz .
We have begun blind search of high- J CO toward high- z submillimeter galaxies .