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

The insufficient power-handling capability of high-temperature superconducting microwave filters has been a serious barrier to their application. To clarify the key parameters for improving the power-handling capability of RF filters based on high-temperature superconductors (HTSs) with microstrip structures, we synthesized bandpass filters with different layouts using several kinds of HTS thin films and performed third-order intermodulation measurements on them. The experimental results indicate that increasing the film thickness and utilizing molecular-beam-epitaxy-grown films of NdBa₂Cu₃O₇ (NBCO) are effective in obtaining microstrip filters with high power-handling capability. For NBCO filters, we also investigated the effects of oxygen annealing, passband width, and the frequencies of the input signals on the power-handling capability.