Optimization of Asymmetric Orthomode Transducer at Terahertz Frequency

For the need of polarization multiplexing, an asymmetric orthomode transducer (OMT) working at 260~325 GHz is demonstrated in this paper. Since the reflection efficient bandwidth of directed port is commonly wider than that of side port in the previous designs, the coupling aperture corresponding to side port is enlarged, which optimizes the performance of the side port and reduces difficulty of high frequency processing while deteriorate directed port a little due to higher discontinuity. Then the first two high-order-modes introduced by discontinuity and asymmetry is investigated. To achieve a better polarization isolation, the size of the common port is reduced, which decreases the cross-polarization component introduced by structural design and fabrication errors with the help of the suppression of the highorder-modes. As a result, the bandwidth and polarization isolation are increased. The return loss is less than -15db and the polarization isolation is better than -50db in the working frequency.