Waveguide-to-planar circuit transition for millimetre-wave detectors

A novel design of a waveguide to microstrip or coplanar waveguide transition using a unilateral finline taper is presented. The transition from the unilateral finline mode to the TEM microstrip mode is done directly, avoiding the antipodal finline tapers that have commonly been employed. This results in significant simplification of the design and fabrication, and shortening of the chip length, thereby reducing insertion loss. Also presented are designs at 90 GHz that can be employed in superconducting tunnel junction mixers or transition edge sensor bolometers, and scale-model measurements at 15 GHz.