Octave Bandwidth Orthomode Transducers for the Expanded Very Large Array

Quadruple-ridge orthomode transducers (OMTs) have been designed to operate over a full octave bandwidth for the expanded very large array (EVLA) project. The OMT separates linearly polarized signal components by matching a circular waveguide input to two orthogonal coaxial outputs. The OMT is used in conjunction with a quadrature hybrid to detect circularly polarized signal components. This paper focuses on the 1 GHz-2 GHz L-Band OMT design, which has better than 18.8 dB measured return loss across the band, with no evidence of trapped-mode resonances. The OMT is designed with an emphasis on performance, ease of tuning and manufacturability since a large number of units are needed for the array application. Extensive parametric analyses were carried out, and nominal dimensions have been set to ensure the devices exceed RF specifications provided the parts are machined to within specified tolerances. With excellent wideband performance and a simplified manufacturing process, the proposed OMT would be amenable to much larger future array projects.