Development of Double-Ridged Wavegide Orthomode Transducer for the 2 MM Band

This paper describes the design and development of the 2 mm band orthomode transducer (OMT) for the Band 4 cartridge receivers of the Atacama Large Millimeter/Submillimeter Array (ALMA). The OMT consists of a double-ridged waveguide followed by a B phi ifot type junction with a main arm and two side arms. The main arm output is a multi-section step transformer followed by an E-plane bend and an oval waveguide to be realized the OMT with a two-split block using conventional Computer Numerical Control (CNC) milling techniques. The prototype OMT shows return loss of better than 20 dB, cross polarization coupling of better than 30 dB and insertion loss of less than 0.4 dB across 125 - 163 GHz. Furthermore, production feasibility was demonstrated through the evaluation of seven OMTs with a production design. The design of the developed OMT is so simple that it is easily scaled to submillimeter frequencies.