Independently Tunable HTS Dual-Band Bandpass Filters Using Dielectric Rods

We have developed a high-temperature superconducting dual-band bandpass filter (DB-BPF) with independently tunable center frequencies. The DB-BPF is designed with stub-loaded hair-pin resonators. Dielectric rods are used to tune the center frequencies of both passbands. For the first passband, the dielectric rods are placed at the center of the resonators while keeping the second passband center frequency almost the same. For the second passband, the dielectric rods are placed at the stub part of the resonators while keeping the first passband center frequency basically the same. The distances between the resonators and dielectric rods are changed to tune the center frequencies. The four-pole DB-BPF was designed to operate at 1.5 GHz with a 15-MHz (1%) bandwidth for the first passband and at 2.0 GHz with a 20-MHz (1%) bandwidth for the second passband. The DB-BPF was fabricated using YBa
₂
Cu
₃
Oy thin film on an Al
₂
O
₃
substrate. The ranges of the center frequency modulation of the first and second passbands were 100 and 110 MHz with no degradation of the low-loss characteristics.