Dual-Band BPF with Independently Controllable Center Frequencies Using Narrow-Closed-Loop Loaded Resonator

To gain separately controlled center frequencies and realize miniaturization, this article presents a dual-band bandpass filter (BPF) adopting narrow-closed-loop loaded resonator (NCLLR). By adjusting two narrow-side positions (namely the size of narrow-closed-loop), center frequencies of two passbands can be independently shifted in a certain area, respectively. Moreover, in order to achieve high selectivity in frequency characteristic domain, tapped-line coupling is applied to introduce three/four transmission zeroes (TZs) on either side of two target passbands. Good characteristics in passbands can be obtained by optimizing coupling gap and tapping position of stepped impedance I/O feed lines. Simulated and measured results are in good agreement.