LOW-TEMPERATURE AND HIGH-TEMPERATURE SUPERCONDUCTING MICROWAVE FILTERS

Stripline and microstrip filters at X-band were designed and fabricated using low- and high-temperature superconductors in quarter-wave, parallel-coupled section configurations. Low-temperature superconducting niobium thin films, deposited on single-crystal sapphire, were used to build two six-pole stripline filters with adjacent passbands and approximately 3 dB crossovers and 1.2% bandwidth. Four- and six-pole microstrip filters were made with in situ epitaxial YBa2Cu3O7 (YBCO) films on LaAlO3 substrates. All the YBCO filters showed 77 K passbands with clean skirts and high out-of-band rejection. The YBCO six-pole filters were made after some initial technology developments, together with a reasonably high degree of repeatability, were established with the fabrication of eight working four-pole filters. The six-pole filters had adjacent passbands with - 28 dB crossovers and 1.5% bandwidth. The results obtained show the potential of high-temperature superconductors for filters with narrow bandwidths and low insertion losses. Furthermore, they show a very rapid rate of development of superconducting filter technology, leading to system demonstrations and subsequent production in the near future.