A New 100-GHz Band Front-End System with a Waveguide-Type Dual-Polarization Sideband-Separating SIS Receiver for the NRO 45-m Radio Telescope

TL;DR

This paper presents a novel 100-GHz dual-polarization sideband-separating SIS receiver system for the NRO 45-m telescope, achieving improved noise performance and simultaneous multi-line observations.

Contribution

The paper introduces a waveguide-type dual-polarization SIS receiver with enhanced noise temperature and image rejection, optimized for the 100-GHz band on the NRO 45-m telescope.

Findings

Achieved single-sideband noise temperatures of 50-100 K over 80-120 GHz.

Demonstrated successful simultaneous observation of multiple CO emission lines.

Improved image rejection ratios over previous systems.

Abstract

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.