Double-Ridged Waveguide Orthomode Transducer (OMT) for the 67–116-GHz Band

A high-performance low-loss high-reflection-loss compact double-ridged waveguide orthomode transducer (OMT) for the 67–116 GHz band has been designed, fabricated, and tested. The focus in the design has been to achieve the best possible performance while keeping the design compact and fabrication as simple as possible. The designed OMT is based on a double-ridged waveguide Boifot junction followed by a main arm with an E-plane bend, and two side arms which are combined into a Y-junction. Wideband performance has been achieved by careful control of the waveguide width at the waveguide junction, and by the use of a variable width septum. The design is very compact and can be fabricated by conventional computer numerical control (CNC) milling techniques in two split blocks. The output waveguides are standard WR-10 rectangular waveguides. Prototype OMTs have been fabricated and tested with good agreement with simulations. The measured insertion loss is around 0.15 dB, the reflection loss is better than 23 dB, and isolation and cross-polarization are lower than – 45 dB at all frequencies. This OMT is intended to be used in cryogenic low-noise receivers for radio astronomy. To the extent of our knowledge, this is the best reported performance for an OMT over a 55% fractional bandwidth at W-band frequencies.