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This paper addresses design and experimental characterization of a two-pole 1.5% bandpass tunable filter operating at 0.9 GHz and 77 K. The filter is based on two YBCO plated KTaO3 disc resonators (0.5-mm-thick, 10 mm in diameter) and utilizes the TM020 mode. The tunability is achieved through the nonlinear DC electric field dependence of the relative dielectric constant of KTaO3. About 5% tuning range is achieved at 500 V driving voltage. Although the insertion losses are relatively high (about -5 dB at 500 V) the shape of the passband is essentially stable. A rather good agreement between simulated and experimental performances is found.
Date of Publication: March 2004