Recent progress on high-temperature superconducting filters

Since the discovery of high temperature superconducting (HTS) materials in 1987, the performance of microwave filters such as insertion loss, selectivity, and out-band rejection has been significantly improved by utilizing HTS films. Nowadays, HTS filters have been widely used in wireless communications, space exploration, satellite communications, and several other fields. HTS filters with a special performance, such as wideband, dual-band or multiband, frequency tunable, and high power-handling capability have been designed and fabricated in recent years to meet the increasing requirements of practical applications and to further extend the application areas. This paper reviews the various types of above-mentioned HTS filters as well as the developments of novel design methodologies.