Design of compact dual-band bandpass filters using λ /2 and combined λ /4 stepped-impedance resonators

[[abstract]]This paper presents a compact dual-band bandpass filter (BPF) that consists of a pair of L-shape half-wavelength (λ/2) stepped-impedance resonators (SIRs) and an inverted Z-shape resonator. The latter is actually a combined structure of two λ/4 SIRs along with a magnetic coupling in between and hence designed to reduce the circuit size. Cross-coupled SIR configuration and 0° tapped-feed structures are adopted to introduce attenuation poles around the passband edges for selectivity improvement. A wider −20-dB upper stopband is achieved by properly separating the third resonant frequencies of the SIRs of different types. The newly designed dual-band BPF was verified by circuit implementation, and a very good agreement between the simulated and measured results was observe