Dual mode cross-slotted filters realized with superconducting films

A planar superconducting single stage dual mode filter has been investigated and tested. The basic element of the device is a square patch resonator diagonally crossed by unequal slots to provide both a size reduction and a simple way to couple the two degenerate modes. The effect of further cuts, realized on the conductor surface, is also investigated with respect to the power handling capability and miniaturization requirements. Two different filter 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 and intermodulation measurements. Third order products start to appear above the noise floor (-120 dBm) at input power P(in)approximate to -20 dBm, whereas thermomagnetic breakdown is observed above 20 dBm. (C) 2000 American Institute of Physics. [S0003- 6951(00)04552-6].