HIGH-POWER HTS MICROSTRIP FILTERS FOR WIRELESS COMMUNICATION

The performance of narrowband microstrip filters with low insertion lo ss and high power-handling capabilities made from YBa2Cu3O7-delta (YBC O) high-temperature superconducting (HTS) thin films is presented, Res ults are shown for two different designs that were chosen to optimize the power-handling capability. Both filters have a 2-GHz center freque ncy and 5 poles that incorporate coupled resonators with 10-Omega inte rnal impedances, They were made on 5 cm-diameter LaAlO3 substrates, Bo th designs use parallel-coupled feed lines to avoid current crowding, The first design includes backward- and forward-coupled filters, has 1 % bandwidth, and has handled over 25 watts of input power at 10 K with less than 0.25 dB compression, The second design has 1.2% bandwidth a nd uses only forward-coupled resonators. The dissipation loss is less than 0.2 dB at 35 K and it has a third-order intercept of 62 dBm. Anot her similar filter handled 36 watts of power at 45 K with less than 0. 15 dB compression across the passband. We have developed a technique t o visualize the power dissipation of the filter by observing the bubbl es created by the filter when submerged in liquid helium, showing area s with local defects or where the current distribution is at its peak value, We also discuss several planar high-power filter issues, includ ing material selection and fabrication, device configuration trade-off s, filter structure optimization, and design approaches to maximize po wer-handling capacity.