Optimization of materials and design for electrically tunable microwave filters

Electrically tunable microwave band-pass filters are fabricated using a high-temperature superconductor and tunable dielectrics based on SrTiO3. The design of the filters is optimized for bandwidth stabilization and proper impedance matching. The properties of the tunable dielectric are optimized through adjustments of the growth parameters and the use of buffer layers. The optimized filter is characterized by an insertion loss less than 2.5 dB, unloaded quality factors ranging from 452 to 709, and a 4.6% tuning range at ± 140 V.