Dual-side backward coupler waveguide orthomode transducer for the 3 mm band

Abstract

We describe the design, construction, and characterization results of a waveguide Orthomode Transducer (OMT) for the 3 mm band (84-116 GHz.) The OMT is based on a symmetric backward coupling structure and has a square waveguide input port (2.54 mm × 2.54 mm) and two single-mode waveguide outputs: a standard WR10 rectangular waveguide (2.54 mm × 1.27 mm,) and an oval waveguide with full-radius corners. The reverse coupling structure is located in the common square waveguide arm and splits one polarization signal in two opposite rectangular waveguide sidearms using broadband -3 dB E-plane branch-line hybrid couplers. The device was optimized using a commercial 3D electromagnetic simulator. The OMT consists of two mechanical blocks fabricated in split-block configuration using conventional CNC milling machine. From 84 to 116 GHz the measured input reflection coefficient was less than -17 dB, the isolation between the outputs was less than -50 dB, the cross polarization was less than -30 dB, and the transmission was larger than -0.35 dB at room temperature for both polarization channels. The device is suitable for scaling to higher frequency.