Development of a 385-500 GHz Orthomode Transducer (OMT)

The 19th International Symposium on Space Terahertz Technology

Mamoru Kamikura1,2,3, Masato Naruse1,2, Shin’ichiro Asayama2, Naohisa Satou2, Wenlei Shan4, and Yutaro Sekimoto1,2

Others  :  http://www.nrao.edu/meetings/isstt/papers/2008/2008557562.pdf
PID  :  49614

来源: CEUR

【 摘 要 】

We report on the developmentof an orthom ode transducer (OMT) for ALMA Band 8 (385-500 GHz). The OMTis a scaled model of that of ALMA Band 4 (125-163 GHz), whichhas a B φifot junction and a doubleridge. The tr ansmission lossof the OMTat4 K was derived tobe 0 .4-0.5 dBfromnoisemeasurements with an SIS mixer. The polarization isolation wasmeasured tobe la rger t han 20 dB from quasiopticalmeasurements. For electromagnetic d esign, effe cts of mechanical er rors havebeen studied and the n a r obust de signwith allowable mechanical errors of 10 μm has been obtained.I. INTRODUCTIONAn orthomode transducer (OMT) is a passive waveguidedevice that separates a received signal by a feed horn into itstwo orthogonal linearly polarized components. Forsubmillimeter receivers, the conventional way to separateorthogonal polarizations is to use a wire grid, which is aquasioptical device that consists of free-standing wires. Optical systems of a dual polarization receiver with a wiregrid or an OMT are shown in Fig.1. The merits and demeritsof an OMT compared with a wire grid are the following: