Compact and high-selectivity microstrip bandpass filter using two-stage twist-modified asymmetric split-ring resonators

A compact and high frequency selectivity two-stage microstrip bandpass filter is designed and experimentally demonstrated. Such a kind of filter is composed of two pairs of twist-modified asymmetric split-ring resonators (SRRs) to achieve three transmission poles within the passband and four transmission zeros at low and high rejection bands. Sharply out-of-band reductions contributing to the high frequency selectivity are obtained by properly detuning the gaps among the SRRs. The measured results show that the proposed filter with dimensions of 0.088 × 0.088λ² has a 3 dB passband of 15.2% centred at 1.98 GHz. This filter can be flexibly integrated in miniaturised radio-frequency/microwave circuits.