A Turnstile Quad-Ridge Orthomode Transducer (OMT) for Octave-Bandwidth Receiver Front-Ends (24–51 GHz)

We report on the design, fabrication, and measured results of a turnstile quad-ridge orthomode transducer (OMT) suitable for millimeter-wavelength receivers used in radio telescopes for astronomy. The quad-ridge OMT is directly compatible with a quad-ridge feed horn to implement dual-polarization low-noise receivers that exceed the single-mode bandwidth of a rectangular waveguide. Using a bandwidth of 24–51 GHz, the OMT demonstrated an insertion loss of 0.3–0.4 dB along with cross-polarization leakage and isolation below −40 dB. An OMT is a key part of a dual polarization receiver front-end, and our long-term goal is to realize low-noise, wideband receivers for radio astronomy utilizing ridge waveguides throughout the entire front-end. Design details are provided for each ridge waveguide feature within the OMT, including a quad-ridge waveguide turnstile junction, $E$ -plane bend, and $E$ -plane T-junction. To facilitate future layouts and integration, additional ridge waveguide component designs have been included for a 3-dB coupler, $H$ -plane bend, and $H$ -plane T-junction.