Dual mode cross-slotted filters realized with superconducting films

A planar superconducting single stage dual mode filter has been investigate d and tested. The basic element of the device is a square patch resonator d iagonally crossed by unequal slots to provide both a size reduction and a s imple way to couple the two degenerate modes. The effect of further cuts, r ealized on the conductor surface, is also investigated with respect to the power handling capability and miniaturization requirements. Two different f ilter topologies operating in C band with 1% fractional bandwidth have been designed and fabricated using Nb and YBa2Cu3O7 films grown on 10x10x0.5 mm (3) LaAlO3 (100) substrates. Device response is studied performing power an d intermodulation measurements. Third order products start to appear above the noise floor (-120 dBm) at input power P(in)approximate to -20 dBm, wher eas thermomagnetic breakdown is observed above 20 dBm. (C) 2000 American In stitute of Physics. [S0003- 6951(00)04552-6].