Orthomode transducer design for the broad W-Band CARUSO focal plane array receiver

The design, fabrication, and performance of a millimeter-wave waveguide orthomode transducer (OMT) operating over an extended W-band frequency range 70–116 GHz is presented. The OMT has been designed for integration within a cryogenic radio astronomy focal plane array millimeter-wave receiver. In addition to delivering necessary millimeter-wave performance, a custom mechanical housing incorporating suitable waveguide interfaces is required. Within the OMT, a turnstile junction performs polarization separation of a signal entering a bespoke circular waveguide interface into two orthogonally polarized outputs via WR10 standard waveguide flanges. The device’s internal architecture was optimized using a combination of proprietary software and a commercially available 3-dimensional electromagnetic field analysis package. In order to demonstrate required performance, compactness and reliable production, two approaches were taken with respect to device mechanical fabrication: platelet and split block direct machining methods. Both structures were manufactured and tested at room temperature. Due to advantages in machining and assembly, the split block concept was selected for inclusion with the array receiver.