A wideband bandpass filter using combined λ/4 Stepped-Impedance Resonators

This paper presents a wideband bandpass filter (BPF) designed using novel multi-mode resonators (MMRs). The MMR is formed by combining two quarter-wavelength ( lambda/4 ) stepped-impedance resonators (SIRs) in a proper fashion. The fundamental resonant frequency of the inherent lambda/4 SIR and that of the embedded half-wavelength ( lambda/2 ) SIR were designed to be located in the passband of the BPF. Experiments on a second-order wideband BPF were carried out for validating the filter design. The fabricated BPF was measured to have a large bandwidth of 1:2.1 with a minimum insertion loss of only 0.35 dB and a small group-delay variation of not more than 0.15 ns in the passband.