An electrically tunable high-T/sub c/ microwave bandpass filter

A prototype superconducting microwave bandpass filter whose center frequency can be tuned electrically is designed, modeled, fabricated, and tested. The tuning is accomplished via self-heating of a superconducting control line located next to a superconducting resonating element. Both the single-pole microstrip filter and the control line are patterned from a single thin-film layer of YBa/sub 2/Cu/sub 3/O/sub 7/. When the critical current of the control line is exceeded, at an operating temperature of 77 K and below, the center frequency of 13 GHz shifts down by as much as 50 MHz, with only a modest increase of insertion loss. This performance is successfully modeled in terms of the change in the kinetic inductance of the filter element caused by heating the control line. Switching speeds in excess of 1 kHz are demonstrated. Implications of these results for the design of an improved tunable high-temperature superconducting filter are discussed.