Compact turnstile quad-ridge orthomode transducer with octave bandwidth for radio astronomy applications

Abstract

A novel wideband orthomode transducer (OMT) featuring a folded-arm turnstile junction covering a 2:1 frequency band is employed to achieve an effective structure while meeting the strict OMT requirements for radio astronomy applications. The turnstile junction is designed with two symmetry planes to ensure separation between perpendicular polarizations and the effective management of higher order modes. Within the throat of the turnstile junction, stepped cylinders serve as scattering elements and matching stubs to ensure efficient impedance matching between the quad-ridge circular waveguide at the input and the single-ridge rectangular waveguides at the output. The folded arms play a pivotal role in achieving excellent matching while significantly reducing the overall size. Considering the significance of developing wideband radio astronomy receivers with minimal noise, this design demonstrates a precisely engineered compact OMT, with tuned bends, junctions, and delivers simulated return loss better than 20 dB while maintaining cross-polarization performance well below 65 dB within the specified 20-40 GHz frequency range.