A superconducting microwave switch

We describe a superconducting microwave switch. The switch comprises a tapering microwave transmission line which can he switched from a very low loss ON state to a high impedance OFF state with a DC voltage applied to the transmission line through a bias-tee. Switching is essentially thermal in nature, occurring due to the formation of a 'hot spot' in the transmission line. Thermal runaway is avoided through the use of voltage rather than current biasing. Once switched, the transmission line attenuates the applied microwave signal. An isolation of 20 dB is readily achievable. The intrinsic response time of the hot spot to applied microwave fields was estimated to be approximately 1 /spl mu/s by measuring the frequency dependence of the transmitted signal.< >