Silicon Membrane-Based Waveguide-to-Superconducting CPW Transitions at 2 mm Band

In millimeter and submillimeter superconducting receivers, which are widely applied in radio astronomical observations, waveguide-to-planar transmission line transitions are key components connecting waveguide medium and the superconducting planar circuit. Although conventional quartz substrate-based transitions perform well for single-pixel receivers, these waveguide probes are not suitable for imaging arrays because their narrow chip space prohibits a higher degree integration of superconducting circuits. For multi-beam receiving applications, we have demonstrated fully functional monolithic microwave integrated circuit superconductor-insulator-superconductor (SIS) mixers with on-chip silicon membrane-based transitions at 2 mm wavelengths. In the present work, we aim to assess the transition as a stand-alone component and investigate its bandwidth potential. We designed a full-height waveguide transition which covers 125-211 GHz, more than 50% fractional bandwidth. The experimental study was carried out by performing cryogenic measurements of the transmission of a back-to-back probe pair with a mm-wave network analyzer. The measured transmission is well consistent with the simulated one in the frequency range of 125-170 GHz, which is covered by the network analyzer in this measurement.