VLBI Exploration of Radio Astrometry (VERA) is a VLBI facility operated by the National Astronomical Observatory of Japan. It comprises four 20 m radio telescopes located across the country. VLBI observations at 86 GHz allow us to explore the jet base of nearby active galactic nuclei. In recent years, the development of the 86 GHz receiver systems at the East Asia VLBI Network (EAVN) has started. Currently, only three Korea VLBI Network (KVN) antennas provide 86 GHz VLBI capability in the member stations of EAVN. The participation of VERA in the 86 GHz VLBI observations will boost resolution, sensitivity, and dynamic range. Therefore, we are developing a new 86 GHz low noise receiver system to be installed at VERA Mizusawa and Ishigaki stations. We are considering a cooled circular polarization receiver covering a wide frequency range of 67−116 GHz with the capability of cooling HEMT amplifiers. We are developing a room temperature 2 side band (2SB) system for down-converting signals in the 67−116 GHz band. Recently developed room-temperature mixers with an IF frequency over 25 GHz could cover most of the 67−116 GHz RF signals in a single observation. In this poster, we will discuss the development progress of the 2SB receiver and the design status of the cooling Dewar.
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.
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