Development of a Smooth Taper Double-Ridge Waveguide Orthomode Transducer for a New 100 GHz Band Z-Machine Receiver for the NRO 45-m Radio Telescope

A smooth taper double-ridge waveguide orthomode transducer (OMT) has been designed for the new 100 GHz band receiver system on the Nobeyama Radio Observatory (NRO) 45-m radio telescope. The OMT consists of a smooth taper double-ridge waveguide followed by a Bøifot type junction with a main arm and two side arms. The main arm output is a smoothed tapered transformer followed by an E-plane bend and an oval waveguide. This design facilitates the fabrication of the OMT using split blocks machined on a CNC (computer numerical control) machine. The OMT shows a return loss of better than 18 dB, a polarization isolation of better than 28 dB, and an insertion loss of less than 0.5 dB across the 74–116 GHz, and also demonstrated the excellent performance on the NRO 45-m radio telescope.