Development of a wideband receiver for dual-band and dual-polarization observations in 230 and 345 GHz bands

Abstract

We have been developing a wideband heterodyne receiver for simultaneous observations in isotopologue CO lines of J = 2-1 and J = 3-2 transitions with dual-polarization. To achieve these simultaneous observations, a wideband frequency separation system was required in the radio frequency circuit because the intermediate frequency range of the superconductor-insulator-superconductor mixer is narrower than the frequency range of the CO lines from J = 2-1 to J = 3-2. As the frequency separation system, a waveguide multiplexer that connects three types of diplexers was applied. The prototype multiplexer was already developed and installed in the 1.85-m radio telescope. Then, we succeeded in commissioning observations simultaneously in 230 and 345 GHz bands with single polarization. We are currently working on improving the multiplexer and developing a 90° differential phase shifter and a wideband orthomode transducer (OMT). The 90° differential phase shifter and OMT can be combined to operate as a circular polarizer. We are planning to realize observations of both linearly and circularly polarized waves by using the OMT and circular polarizer, respectively. A part of this development can contribute to the future development of Atacama Large millimeter/submillimeter Array and Very Long Baseline Interferometry telescopes. In this paper, we describe the development of the prototype wideband receiver and the development status of the OMT, circular polarizer, and a new multiplexer.