Mechanical tuning of Superconducting lumped element filter

The tunable filter has variable center frequency (f₀) and variable bandwidth (BW) that can be adapted to software defined radio. In our mechanical tunable filter, capacitance of each element is changed by motion of dielectric plate that is located above the capacitive elements. The dielectric plates are moved by piezoelectric bimorph actuators. Tuning test of the f₀ in a cryocooler is performed using an actual superconducting filter fabricated with YBa₂Cu₃O_y thin film deposited on an MgO (100) substrate. Taking into account of the effective change of parallel capacitance to ground plane by movement of dielectric plates above the element, we choose the coplanar wave guide type filter that has the ground plane on top side of the substrate. Suitable design of the mechanically tunable superconducting lumped element filter is discussed.