A Compact Asymmetric Waveguide Orthomode Transducer for Millimeter-Wave Applications

A compact asymmetric waveguide orthomode transducer (OMT) with broad bandwidth and high isolation is presented in this letter. A novel combined transition-bending structure is proposed within the common arm in the design of the OMT branching T-junction. It implements the E-/H-plane 90° waveguide bends and the square-to-rectangular waveguide transition for both polarization sidearms. Its multiple roles help to reduce the geometry discontinuities and improve the matching bandwidth. The measurements demonstrate that the OMT achieves higher than 50 dB isolation level between the two modes and better than 18 dB return loss from 30.3 to 36.3 GHz (18%). Furthermore, the isolation level is typically 60 dB over 50% of the operation bandwidth. The insertion loss of each polarization is below 0.23 dB for a single OMT. The overall size of the OMT functional section is reduced to
$1.55\,\,\lambda _{0}\times 1.45\,\,\lambda _{0}\times 0.78\,\,\lambda _{0}$
.