Design of HTS Bandpass Filters With High-Frequency Selectivity

This brief affords a novel implementation of the high-temperature superconductivity (HTS) bandpass filters with excessive frequency selectivity and an exact out-of-band rejection due to the new modified coupled feed lines and coupled-line stub-loaded resonators. Firstly, the new coupled feed line is structurally modified in contrast to the parallel-coupled line by loading short-circuit branches at the tails. It has impedance matching and extra transmission poles, which make the filters have a large working passband, along with altering the electrical size of the loaded branches to approve the transmission zeros to be assigned. Then, the coupled-line stub-loaded resonators generate a pair of transmission zeros out of the desired passband, improving the filter's frequency choice function. Finally, to affirm this design, a prototype of the introduced HTS bandpass filter with excessive selectivity and appropriate rejection is designed and fabricated on the MgO substrate with YBCO thin films. The precise settlement between simulation and measurement establishes the best overall performance in phrases of high-frequency selectivity and proper out-of-band rejection level.