Korean VLBI Network Receiver Optics for Simultaneous Multifrequency Observation: Evaluation

Abstract

ABSTRACTWe have developed a new millimeter wave receiver system with input optics that support simultaneous observations in four bands of 22, 43, 86, and 129 GHz to facilitate calibrating tropospheric phase fluctuations for millimeter-wave VLBI observations. In order to make simultaneous observations in four bands pointing at the same position in sky, it is crucial that errors among the beams from any misalignments should be kept small. After doing the beam alignment in the laboratory, on-site test observations were carried out so as to evaluate the performance. The result is that the beam centers of the four bands with reference to the 86 GHz beam center were aligned within 2″ over most of the elevation range of the Korean VLBI Network (KVN) 21 m telescope. Measured telescope aperture efficiencies including the multiband receiver optics are 65% at 22 GHz, 62% at 43 GHz, 57% at 86 GHz, and 38% at 129 GHz. Through this novel optics covering wide RF bandwidth effectively, we can simultaneously observe the SiO maser transitions at 43, 86, and 129 GHz and in addition the water maser line at 22 GHz.