We report on a novel waveguide-to-substrate transition with prospective use for broadband mixer design. The transition employs a substrateless finline, i.e., a unilateral finline structure with the substrate removed between the fins. This distinctive feature diminishes the overall insertion loss and facilitates matching with the waveguide. The transition is designed on a thin silicon substrate covered by a superconducting niobium thin layer. An auxiliary Au layer situated on top of the Nb layer provides grounding for the fins and facilitates the mounting process in the split-block waveguide mount. Aiming to compare simulations with measurements, a back-to-back transition arrangement for the 211–373 GHz frequency band was designed, fabricated, and characterized at cryogenic temperatures. The simulation results for the back-to-back structure show an insertion loss of less than 0.6 dB in the whole band, i.e., 0.3 dB per transition. Furthermore, a remarkable fractional bandwidth of 55% with a return loss better than 15 dB is predicted. Experimental verification shows consistent results with simulations.

中文翻译：

---

基于单边无基板鳍线结构的基板过渡波导：设计、制造和表征

我们报告了一种新颖的波导到基板的过渡，可用于宽带混频器设计。该过渡采用无衬底鳍线，即单边鳍线结构，其中衬底在鳍之间被移除。这种独特的特性降低了整体插入损耗并促进了与波导的匹配。过渡层设计在覆盖有超导铌薄层的薄硅衬底上。位于 Nb 层顶部的辅助 Au 层为鳍片提供接地，并有助于拆分块波导安装中的安装过程。为了将模拟与测量进行比较，在低温下设计、制造和表征了 211-373 GHz 频段的背对背过渡布置。背对背结构的仿真结果表明，整个频段的插入损耗小于 0.6 dB，即每次转换为 0.3 dB。此外，预计会有 55% 的显着分数带宽，回波损耗优于 15 dB。实验验证显示与模拟一致的结果。