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A novel three-pole electrically tunable narrow bandpass filter has been fabricated from bi-layer YBCO/Ba0.05Sr0.95TiO3 thin films. At 77 K, and without bias, the filter has a center frequency of 3.50 GHz and 5.8% bandwidth. Independent application of dc bias to each of the resonators of 120, 182, and 100 V shifted the center frequency to 3.68 GHz. The insertion loss was less than 1.4 dB and return loss was better than 20 dB. A similar filter was made using bi-layer Ag/Ba0.5Sr 0.5TiO3 thin films and measured at room temperature. The insertion loss of the filter was, as expected, much higher, although it showed improved tunability as compared with the YBCO version.
Microwave Theory and Techniques, IEEE Transactions on (Volume:56 , Issue: 11 )
Date of Publication: Nov. 2008