High-Selectivity High-Temperature Superconducting Triband Balanced Bandpass Filter Using Symmetric Stub-Loaded Resonator

In this article, a compact high-temperature superconducting (HTS) fourth-order triband balanced bandpass filter (BPF) is developed by using a newly proposed multimode symmetric stub-loaded resonator (SSLR). The differential-mode and common-mode (CM) resonance characteristics of the SSLR are analyzed based on the transmission line theory and the even-/odd-mode method. Then, the configuration and coupling topology of a fourth-order triband balanced BPF are proposed, and variations in behaviors of the design parameters versus the structural dimensions of the filter are investigated. Finally, the triband balanced BPF operating at 1.56/4.22/5.8 GHz is designed and fabricated using HTS yttrium barium copper oxide (YBCO) films deposited on a MgO substrate. The measured filter response agrees well with the simulated one and shows excellent properties such as low insertion loss, high frequency selectivity, and larger CM suppression.