Two-Pole Tunable Bandpass Filter Based on YBCO Plated Single Crystal KTO Disk Resonators

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 KTaO/sub 3/ disc resonators (0.5-mm-thick, 10 mm in diameter) and utilizes the TM/sub 020/ mode. The tunability is achieved through the nonlinear DC electric field dependence of the relative dielectric constant of KTaO/sub 3/. 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.