Broadband Waveguide-to-Substrate Transition Using a Unilateral Etched Finline Structure

Paper in proceeding, 2019

We present a novel broadband waveguide-tosubstrate transition that aims to be used for broadband mixer design. The transition consists of a unilateral finline structure with etched substrate between the fins. This particular feature reduces the overall insertion loss and facilitates matching with the waveguide. The transition is designed of a thin silicon substrate covered by a superconducting niobium thin layer. An auxiliary gold layer situated on top of the Nb-layer provides grounding for the fins and facilitates a simple mounting process in the split-block waveguide mount. In order to compare simulations with measurements, a back-to-back arrangement was designed and simulated using HFSS in the 211-373 GHz frequency band. The back-to-back simulation results show an insertion loss of less than 0.3 dB in the whole band. Furthermore, a fractional bandwidth of 55% with a return loss better than 15 dB is achieved