Design of HTS Modified Double-Strip Resonator Filter Structure for Transmit Filter Applications

A high-temperature superconductor modified double-strip resonator filter structure for transmit filter application is presented. The filter is constructed with a double-strip resonator and a center pin of the SMA connector as a feed line for improving the power handing capability and frequency responses. A double-strip resonator reduces the current concentration at the edges of the resonator compared with that of a conventional single strip resonator due to the increase of the effective film thickness. A center pin placed at the center of the double-strip resonator is introduced to improve the implementation of the filter and the frequency response. A double-strip two-pole dual-mode square patch filter with a 5.0-GHz center frequency and 100-MHz bandwidth was designed. The filter was fabricated using YBa₂Cu₃O_y thin films on CeO₂-buffered Al₂O₃ substrates. A three-dimensional electromagnetic simulator was used to design and investigate the filter. The measured frequency response of the filter was in reasonable agreement with the simulated one. The measured power-handling capability of the filter was more than 31 W (44.9 dBm) at 60 K.