2 GHz tunable superconducting band-pass filter using a piezoelectric bender

We have developed a 2 GHz tunable superconducting band-pass filter using a piezoelectric bending actuator. The filter is a 12-pole microstrip line structure on 50 mm diameter LaAlO3 substrate and has low loss and sharp skirt characteristics. The center frequency was 1.94 GHz and the attenuation characteristics were 30 dB at I and 3 MHz apart from the lower and higher band-edge, respectively. A sapphire (Al2O3) plate was stacked on the filter with an air gap and the gap thickness was controlled electrically from the outside of a refrigerator using a piezoelectric bending actuator. The center frequency of the filter could be adjusted within I I MHz in such a manner that the low loss and sharp skirt characteristics were not degraded. (C) 2002 Elsevier Science B.V. All rights reserved.