High-temperature superconducting dual-spiral resonators and their application in filter miniaturization

Dual-spiral resonators, each of which consists of two spirals connected in series, exhibit much smaller sizes than existing miniature microstrip reson ators, and their geometrical layouts enable them to be easily integrated in to microwave circuits. Dual-spiral resonators have very high quality factor s if they are fabricated with high-temperature superconducting (HTS) thin f ilms. HTS dual-spiral resonators are very suitable for developing miniature filters in MIC and MMIC cellular communication systems. A full-wave electr omagnetic simulator is used to calculate the resonant properties of dual-sp iral resonators, and numerical results are reported. As an application exam ple of HTS dual-spiral resonators, a three-stage bandpass filter with centr al frequency 633 MHz is designed and fabricated with YBa2Cu3O7-delta thin f ilms deposited on a 20 mm x 8 mm x 0.5 mm LaAlO3 substrate. Experiments sho w that the dual-spiral resonator structure presented in this paper is very effective for filter miniaturization.