Third-order intermodulation measurements of 2 GHz microstrip bandpass filters based on high-temperature superconductors

To elucidate the key parameters for improving the power-handling capability of rf filters of high-temperature superconductors with microstrip structures, we synthesize bandpass filters with different layouts using several kinds of thin film high-temperature superconductors, and perform third-order intermodulation measurements on them. The third-order intercept (IP3) at 70 K is found to increase from +53 dBm to +65 dBm as the film thickness increases from 0.62 µm to 0.80 µm for the filters of YBa2Cu3O7 (YBCO). We find that filters made from films of NdBa2Cu3O7 (NBCO) grown by molecular-beam epitaxy yield higher IP3 values than those made from commercially obtained YBCO films. These experimental results indicate that increasing the film thickness and utilizing MBE-grown NBCO films are effective in obtaining high-power-handling microstrip filters.