期刊
PUBLICATIONS OF THE ASTRONOMICAL SOCIETY OF JAPAN
卷 69, 期 6, 页码 -出版社
OXFORD UNIV PRESS
DOI: 10.1093/pasj/psx098
关键词
instrumentation: detectors; radio lines: ISM; telescopes
资金
- Japan Society for the Promotion of Science(JSPS) [26-12320]
- JSPS [22244014, 26247026]
- Toray Science Foundation
- Grants-in-Aid for Scientific Research [15K05025, 16H02167, 22244014, 26247026] Funding Source: KAKEN
A new sideband separation method was developed for use in millimeter-/submillimeter-band radio receivers using a novel waveguide frequency separation filter (FSF), which consists of two branch line hybrid couplers and two waveguide high-pass filters. The FSF was designed to allow the radio frequency (RF) signal to pass through to an output port when the frequency is higher than a certain value (225 GHz), and to reflect the RF signal back to another output port when the frequency is lower. The FSF is connected to two double sideband superconductor-insulator-superconductor (SIS) mixers, and an image rejection ratio (IRR) is determined by the FSF characteristics. With this new sideband separation method, we can achieve good and stable IRR without the balancing two SIS mixers such as is necessary for conventional sideband-separating SIS mixers. To demonstrate the applicability of this method, we designed and developed an FSF for simultaneous observations of the J = 2-1 rotational transition lines of three CO isotopes ((CO)-C-12, (CO)-C-13, and (CO)-O-18): the (CO)-C-12 line is in the upper sideband and the others are in the lower sideband with an intermediate-frequency range of 4-8 GHz at the radio frequency of 220/230 GHz. This FSF was then installed in the receiver system of the 1.85m radio telescope of Osaka Prefecture University, and was used during the 2014 observation season. The observation results indicate that the IRR of the proposed receiver is 25 dB or higher for the (CO)-C-12 line, and no significant fluctuation larger than 1 dB in the IRR was observed throughout the season. These results demonstrate the practical utility of the FSF receiver for observations like extensive molecular cloud surveys in specified lines with a fixed frequency setting.
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