Wideband OMT for the 210–373 GHz Band With Built-In 90° Waveguide Twist

In this article, we present the design of a wideband orthomode transducer (OMT) that aims for the frequency band 210–373 GHz. The OMT employs a modified Bøifot layout and is optimized to fit into the tight spatial constraints, e.g., of the ALMA cartridge. The OMT layout harmonizes the receiver cartridge components for both polarizations by allowing the use of the same configuration and components in both polarization chains because of the OMT outputs’ colinear positioning. The OMT features a built-in novel broadband 90° waveguide twist, which minimizes the insertion RF loss by removing the H-split waveguide while eases receiver component integration with the 2SB mixers in the ALMA cartridge. The manufactured OMT was characterized by direct measurements with a VNA employing frequency extension modules. The waveguide adapters were used accommodating the OMT waveguide ports having dimensions 760 × 760 μm for the input port and 380 × 760 μm for the output ports to the VNA extension modules. The OMT demonstrated the cross pol better than –25 dB across 95% of the frequency band, the output reflections better than 15 dB, and the RF insertion loss better than 0.8 dB.