A VHF-Band Dual-Narrowband HTS Filter Using Superconducting Dual-Composite Right-/Left- Handed Resonators: Design and Implementation

In this article, a miniaturized dual-narrowband high temperature superconducting (HTS) bandpass filter of very high frequency band is proposed. The newly developed superconducting dual-composite right-/left-handed (SD-CRLH) resonator with wide stopband nature, high unloaded quality factor (
Q_u
), and miniaturized size is theoretically studied. To support filter design, equivalent circuit model of SD-CRLH resonator to give insight into inherent performance of widened stopband is established and operating mechanism of electromagnetic (EM) coupled pairs is explored. To ensure feasibility of presented design theory, a sixth-order dual-narrowband HTS filter centering at 186.9/209.9 MHz with two independently operating channels is designed, fabricated, and measured. Meanwhile, cross coupling and transversal interference theory are applied to generation of six desired out-of-band transmission zeros. Close-to-band attenuation greater than 80 dB and high isolation between dual-band validate the ultrahigh selectivity. Good agreement between EM simulated and measured results can be observed, and thus the design concept has been demonstrated as a good candidate to enhance filtering performance of HTS filters.