Tunable and adaptive bandpass filter using a nonlinear dielectric thin film of SrTiO3

We have prepared an electrically tunable and adaptive 3-pole half-wave bandpass coplanar waveguide filter incorporating a 1.2-μm-thick paraelectric SrTiO3 bottom layer and a 0.4-μm-thick superconducting YBa2Cu3O7−x top electrode layer on a LaAlO3 substrate. By applying a separate bias voltage on each pole and also on each coupling capacitance of the device at 4 and 76 K, the filter response is not only fine tuned to achieve symmetric and optimized filter characteristics with less than 2% bandwidth centered around 2.5 GHz, but also broadband tuned to shift the passband by more than 15%.