Miniaturised dual-band filter with high selectivity using split ring scheme

A novel miniaturised dual-band bandpass filter (BPF) using improved split ring λ/4 resonator and stepped impedance resonator (SIR) is proposed. A simple analysis is given for each resonator. By tuning the geometric parameters of the resonators, the two passbands of the BPF can be adjusted separately. Source-load coupling is adopted to achieve more transmission zeros in the stopband. The new dual-band BPF, which has a miniature circuit size of 0.18 × 0.18λg, presents narrow and sharp passband characteristics. Good agreement is found between simulated and measured results, which verify the high-frequency selectivity.