Quarter-Wavelength Stepped-Impedance YBCO Resonators for Miniaturized Dual-Band High-Tc Superconducting Filters

A dual-band high-temperature superconducting (HTS) bandpass filter (BPF) is proposed for wireless local area network applications. Using quarter-wavelength stepped-impedance resonators, the designed filter can be miniaturized and shows a dual-band response. The simulation results show the dual-band feature of two passbands at 2.4 and 5.2 GHz, each with a minimum in-band insertion loss of about 0.02 dB. The filter was made out of patterned double-sided deposited YBa₂Cu₃O_y (YBCO) films integrated with a gold-coated housing. The realized HTS BPF shows two passbands at 2.41 and 5.24 GHz with minimum insertion losses of 0.86 and 1.97 dB, respectively. The measured results show a good HTS BPF performance. Moreover, the temperature-dependent center frequencies can be well described by the modified two-fluid model based formulas, indicating that the frequency shift in HTS BPF is dominated by the temperature dependence of the magnetic penetration depth.