Fully canonical dual-band bandpass filter with λ/4 stepped impedance resonators

A fourth-order fully canonical dual-band bandpass filter (DB-BPF) using λ/4 stepped impedance resonators (SIRs) is presented. In the mainline path, four dual-band λ/4 SIRs are serially coupled by alternative J and K inverters, and cross-couplings, K₁₄ and J_SL, are analytically introduced to achieve two pairs of finite transmission zeros at both sides of each passband. To experimentally demonstrate this attractive fully canonical dual-passband filtering performance, a fourth-order microstrip DB-BPF centring at 1.8 and 5.8 GHz with two pairs of finite transmission zeros for each passband is synthesised and fabricated.