Program and Abstract Book - SRON

19 th International Symposium on Space Terahertz Technology
P12-3
Development of a 385-500 GHz Orthomode Transducer (OMT)
Mamoru Kamikura 1,2 , Masato Naruse 1,2 , Shin’ichiro Asayama 2 , Naohisa Satou 2 ,
Wenlei Shan 3 , and Yutaro Sekimoto 1,2
1
Department of Astronomy, School of Science, the University of Tokyo
2
Advanced Technology Center and ALMA-J project office
National Astronomical Observatory of Japan, National Institutes of Natural Sciences
3
Purple Mountain Observatory, Chinese Academy of Sciences
We present the design and evaluations of an orthomode transducer (OMT) for ALMA Band 8
(385-500 GHz) [1]. An OMT is a passive waveguide polarization diplexer that separates the signal
received by a feed horn into its two orthogonal linearly-polarized components. Because of the
difficulty of fabrication, an OMT has not been developed at frequencies above 320 GHz [2].
The design of the Band 8 OMT was similar to that of the ALMA Band 4 (125-163 GHz)
OMT [3], which is based on an OMT with a Bφifot junction and a double ridged waveguide [4]. In
submillimeter wavelengths mechanical tolerance becomes very severe, so we simulated effects of
mechanical errors on the S-parameters of the OMT. The design is so robust that mechanical errors
of 10 μm do not affect the performance of the OMT.
The polarization isolation and the transmission loss of the Band 8 OMT were evaluated. The
polarization isolation of the OMT measured to be larger than 25 dB with quasi-optical
measurements. The transmission loss of the OMT at 4 K was determined to be 0.4 dB from noise
measurements with a DSB mixer.
References
[1] Y. Sekimoto et al., this conference.
[2] E.J. Wollack and W. Grammer, “Symmetric Waveguide Orthomode Junction,” 14 th ISSTT, pp.
169-176, 2003.
[3] S. Asayama et al., 2008, in preparation.
[4] G. Moorey, R. Bolton, A. Dunning, R. Gough, H. Kanoniuk, and L. Reilly, “A 77-117 GHz
Cryogenically Cooled Receiver for Radioastronomy,” Proc. of Workshop on the Applications of
Radio Science, 2006.
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