Compact High-Pole HTS Triband Bandpass Filters Using a New Feeding Structure

We have designed a compact high-pole high-temperature superconducting triband bandpass filter (TBPF) using a new feeding structure. It combines an eight-pole dual-band bandpass filter (DBPF) that uses stub-loaded meander line open-loop resonators with two types of waveguides and an eight-pole single-band bandpass filter (SBPF) that uses meander line open-loop resonators. The DBPF forms the first and third passbands, and the SBPF forms the second one. Using two types of waveguides enables flexible control of the coupling coefficient of the two passbands, and the proposed feeding structure enables the external quality factor of each passband to be controlled. The TBPF was designed and analyzed using an electromagnetic simulator based on the moment method. The center frequencies of the three passbands were 1.5, 2.0, and 2.5 GHz, respectively, with fractional bandwidths of 2.0%. The TBPF was fabricated using double-sided YBa 2 Cu 3 Oy thin film on a 34.0 × 33.0 × 0.5 mm Al 2 O 3 substrate. The measured frequency responses of the filter match the simulated ones well. This filter is advantageous in terms of size miniaturization and high selectivity.