A Dielectric Waveguide Switch based on Tunable Multimode Interference at W-band

This work presents a compact and lightweight dielectric waveguide (DW) switch at W-band, which uses liquid crystal (LC) technology for tuning multimode interference (MMI). The device, designed for 85 to 105 GHz, is based on the interference pattern also known as self-imaging, which occurs due to a higher order mode propagation in a multimode waveguide. If the multimode waveguide is asymmetrically excited, a phase shift difference arises between two occurring field maxima. By placing LC in the region of one field maximum the phase shift can be adjusted by means of the tunable permittivity. This allows to control the interference pattern and therefore the position of the field maximum at the output of the multimode waveguide, where single mode DWs are connected. In the measurements, a port isolation of 40 dB at 94 GHz was achieved, while the other switching configuration shows a port isolation of 10 dB at 110 GHz. For both cases, the input reflection is below −15 dB over the whole frequency range.