Design of a W-band Orthomode Transducer

An orthomode transducer (OMT) is widely employed to launch two perpendicularly polarized waves in a waveguide for frequency reuse and for polarization diversity applications. In this paper, a circular waveguide orthomode transducer operating at W-band is designed, fabricated and tested. First, an OMT is designed by transforming a circular waveguide into a rectangular waveguide with a multi-step transformer to couple one polarization and by introducing a small longitudinal slot in the circular waveguide wall and impedance matching steps to couple the other orthogonal polarization. The designed structure is amenable to fabrication in two split blocks by precision milling operations. Next, the designed OMT is fabricated to required precision after many trials of milling operations. Tests of the fabricated OMT shows good performance: reflection coefficients of less than -20㏈ at all ports, insertion loss of less than 0.5㏈ and isolation of 30㏈.