Novel 500-GHz Band Waveguide Stepped Septum-Type Circular Polarizer with a New High-Accuracy and Very Small Waveguide Fl
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Novel 500-GHz Band Waveguide Stepped Septum-Type Circular Polarizer with a New High-Accuracy and Very Small Waveguide Flange Yutaka Hasegawa 1
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& Hiroyuki Maezawa & Hideo Ogawa
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Received: 26 August 2020 / Accepted: 8 October 2020/ # The Author(s) 2020
Abstract
A new waveguide stepped septum-type circular polarizer (SST-CP) was developed to operate in the 500-GHz band for radio astronomical and planetary atmospheric observations. In a previous study, we developed a practical SST-CP for the 230-GHz band. However, several issues prevent this device being easily scaled down to the 500-GHz band, such as manufacturing dimensional errors and waveguide flange position errors. In this study, we developed a new waveguide flange with a highaccuracy position determination mechanism and a very small size of 10 × 10 mm. We also developed a new fabrication technique to obtain very good flatness for the device’s blank materials by high-accuracy polishing using a resin fixture. Using these new methods, the manufactured 500-GHz band SST-CP achieved a crosspolarization talk level of better than – 30 dB at 465–505 GHz, a device surface flatness of within 3 μm, and also the horizontal positioning error of ± 3 μm. These results indicate that the developed 500-GHz band SST-CP has high performance in the high-frequency band, and thus the new manufacturing methods are effective in the 500-GHz band. Keywords Waveguide . Circular polarizer . VLBI . Flanges
* Yutaka Hasegawa [email protected]–u.ac.jp * Hiroyuki Maezawa [email protected]–u.ac.jp * Hideo Ogawa [email protected]–u.ac.jp
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Department of Physical Science, Graduate School of Science, Osaka Prefecture University, 1-1, Gakuen-cho, Nakaku, Sakai, Osaka 599-8531, Japan
Journal of Infrared, Millimeter, and Terahertz Waves
1 Introduction Radio wave observations in the submillimeter wave band are important in radio astronomy and atmospheric observations, which deal with the distribution of minor molecules. Above the 100-GHz band, there are various important molecular emission lines, such as CO, CS, NH3, O2, and O3. The very long baseline interferometry (VLBI) observation method is one of the greatest advantages of the radio observations. Using VLBI, we can achieve extremely high angular resolution at the microsecond order. For example, the international VLBI observation project the Event-Horizon Telescope (EHT) obtained the world’s first direct imaging of black hole shadows by attaining an angular resolution of 30-μs degrees in the 220-GHz band [1, 2]. A technique for separating orthogonal polarized waves (V/H) or left-/right-handed circular polarized (LHCP/RHCP) waves is often required in radio observations. For example, it is necessary to unify the observation polarization planes in observation telescopes to construct VLBI. To realize this, in the receiver system of VLBI observatories, circular polarization separation is performed before digital sampling [3, 4]. However, in submillimeter wave observations over 100 GHz, it is technically difficult to directly sampl
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