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A new compact microstrip dual-band bandpass filter (BPF) based on multi-mode λ/4 stepped-impedance resonators (SIRs) with separate coupling paths is investigated. The dual-band BPF with a secondorder bandpass response is composed of only two λ/4 SIRs, resulting in a small circuit size. A coupling gap and a common short-ended stub between the two coupled SIRs are used to create the electric and magnetic couplings with separate coupling paths. The bandwidths of the dual-band BPF can be well controlled by adjusting the coupling strengths of the two coupling paths. Thus, a greater design flexibility for the dual-band BPF can be obtained. For demonstration, a secondorder dual-band BPF with a compact size of 0.14 λ g × 0.16 λ g has been designed and fabricated. A good agreement is achieved between simulation and measurement.

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A compact dual-band coupled-resonator quadrature (90 • ) coupler with flexible passband allocation has been presented. By introducing the dual coupling paths between input and output ports, the design flexibility is increased, and thus, a dual-band response can be realized. For demonstration, a dual-band 90 • coupler operating at 1.6 and 2.1 GHz has been designed and fabricated with microstrip technology. The 90 • coupler is formed by only four dual-mode stub-loaded resonators, leading to a compact size, i.e., about 0.27 λ g by 0.27 λ g . A good agreement is achieved between simulation and measurement.Index Terms-Coupled-resonator, dual-band, microstrip, quadrature coupler.