Dual mode superconducting planar filters based on slotted square resonators

A new kind of dual-mode filter based on cross and transverse slotted square resonators is presented. A pair of unequal crossed slots formed on a square patch resonator provides both a reduction of the filter size and a simple and controllable way to couple the two degenerate modes. Transverse cuts opportunely realized on the patch further decrease the operating frequency without any appreciable change in the power handling capability of the device. Three examples of single stage filters operating in C-band with 1% and 10% fractional bandwidth are designed with a commercial 2.5D software and fabricated using Nb and YBa2Cu3O7 films grown on LaAlO3 (100) substrates, The filters response is characterized at different temperatures and the insurgence of non-linearity investigated varying the input power and carrying out intermodulation measurements.