HIGH-POWER HIGH-TEMPERATURE SUPERCONDUCTING MICROSTRIP FILTERS FOR CELLULAR BASE-STATION APPLICATIONS

We report narrowband microstrip filters with low insertion loss and hi gh power-handling capabilities made from YBa2CU3O7-x high-temperature superconducting films. One 5-pole filter on a LaAlO3 substrate, consis ting of backward-coupled and forward-coupled resonators, can handle ov er 27 W input power at 10 K. It has 1% fractional bandwidth and 10-Ohm internal impedance. The insertion loss increase in passband at 10 K, as the input power changed from a few mW to 27 W, is less than 0.25 dB . We also report a forward-coupled microstrip filter centered at 2 GHz , with a 1.2% fractional bandwidth, 10-Ohm internal impedance, and par allel-coupled feed lines. We appled over 10 Ohm to filter at 45 K with out noticeable degradation of the filter performance. The insertion lo ss at 45 K is less than 0.2 dB. The return loss is better than 12 dB.