A turnstile junction waveguide orthomode transducer

An orthomode transducer with a circular waveguide input and two rectangular waveguide outputs is described. The design utilizes a turnstile junction and two E-plane power combiners. A K-band version of this device has been constructed and tested. From 18 to 26 GHz, the input reflection coefficient was less than -19 dB, the cross-polarization was less than -48 dB, and the transmission loss was similar to 0.15 dB. We estimate the mechanical tolerances that would be required to scale this device to the 200-270-GHz band for use in a dual-polarization radio-astronomy receiver.