A 249-GHz Impedance-Tunable Waveguide Transition Using a Microactuator and Flexible Conductive Membrane

A terahertz band (e.g., 150 GHz/300 GHz), with its broad bandwidth and potential for improved angular and distance resolution, is attracting attention for Beyond 5G/6G communication and sensing applications (radar, imager, etc.). However, as frequencies increase and wavelengths shorten, mechanical tolerances during integration can significantly impact performance (reflection, transmission, etc.), necessitating effective compensation mechanisms. In this paper, we verify the performance variations caused by mechanical tolerances in transmission-line-to-waveguide transitions, which integrate chips, substrates, and waveguides to transmit signals generated by the chip or receive signals from external sources. To overcome these challenges, a tunable-membrane microactuator is proposed, which adjusts the position of the back-short in the transition by using a flexible conductive membrane and a microactuator (dimension: $\phi 10$ mm $\times 16$ mm, maximum stroke of the membrane: 707.7 $\mathrm {\mu }$ m, accuracy<1 $\mathrm {\mu }$ m). The proposed waveguide transition comprises a transmission line and a probe integrated on the multi-layer substrate, along with waveguide flanges and the tunable membrane microactuator. Based on simulation and measurement results, this paper demonstrates the capability of the proposed technology to tune the reflection/transmission losses and frequency bandwidth characteristics of a 249-GHz waveguide transition.