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We developed a dual-linear-polarization HEMT (High Electron MobilityTransistor) amplifier receiver system of the 45-GHz band (hereafter Z45), andinstalled it in the Nobeyama 45-m radio telescope. The receiver system isdesigned to conduct polarization observations by taking the cross correlationof two linearly-polarized components, from which we process full-Stokesspectroscopy. We aim to measure the magnetic field strength through the Zeemaneffect of the emission line of CCS ($J_N=4_3-3_2$) toward pre-protostellarcores. A linear-polarization receiver system has a smaller contribution ofinstrumental polarization components to the Stokes $V$ spectra than that of thecircular polarization system, so that it is easier to obtain the Stokes $V$spectra. The receiver has an RF frequency of 42 $-$ 46 GHz and an intermediatefrequency (IF) band of 4$-$8 GHz. The typical noise temperature is about 50 K,and the system noise temperature ranges from 100 K to 150K over the frequencyof 42 $-$ 46 GHz. The receiver system is connected to two spectrometers, SAM45and PolariS. SAM45 is a highly flexible FX-type digital spectrometer with afinest frequency resolution of 3.81 kHz. PolariS is a newly-developed digitalspectrometer with a finest frequency resolution of 60 Hz, having a capabilityto process the full-Stokes spectroscopy. The Half Power Beam Width (HPBW) ofthe beam was measured to be 37$"$ at 43 GHz. The main beam efficiency of theGaussian main beam was derived to be 0.72 at 43 GHz. The SiO maser observationsshow that the beam pattern is reasonably round at about 10 \% of the peakintensity and the side-lobe level was less than 3 \% of the peak intensity.Finally, we present some examples of astronomical observations using Z45.

Z45: A New 45-GHz Band Dual-Polarization HEMT Receiver for the NRO 45-m Radio Telescope