RF Design, Power Handling, and Hot Switching of Waveguide Water-Based Absorptive Switches

This paper presents the first complete water-based waveguide absorptive switch from 25-40 GHz integrated with commercially available micropumps. The design exploits the absorptive properties of water in the microwave and millimeter-wave bands along with innovative techniques to achieve an optimized performance in both switching states. Besides its static RF performance, the hot-switching response is also experimentally characterized. Successful hot-switching measurements are presented for power levels of up to 32 and 0.16 W for circulating and noncirculating water, respectively. This is achieved with a circulation rate of only ~20 mL/min. We also show that this power handling can readily reach 125 and 1250 W if the circulation rate is increased to 30 and 300 mL/min, respectively. In addition, the dynamic scattering matrix under hot-switching conditions is also measured and compared to the cold-switching scattering matrix. Furthermore, critical temperature effects are also studied. In particular, contrary to common wisdom, we show that increased water temperature can result in improved RF isolation with the appropriate waveguide-switching design.