Compact microstrip dual-band bandpass filter and quad-channel diplexer based on quint-mode stub-loaded resonators

Novel compact microstrip quint-mode multi-stub-loaded resonator has been investigated. Meanwhile, its applications to the dual-band bandpass filter (BPF) and quad-channel diplexer have also been proposed. The proposed dual-band BPF is constructed by a single quint-mode resonator, leading to a very small circuit size. Herein, the first three resonant modes are used to form the first passband, while the other two are used to form the second passband. Besides, the proposed quad-channel diplexer is constructed by two different quint-mode resonators, which also occupies a very small circuit size. In this diplexer design, one of the quint-mode resonator is used to realise the passbands for channels 1 and 3, and the other one is used to realise the passbands for channels 2 and 4. For demonstration, a dual-band BPF operating at 0.9 and 2.2 GHz with a size of 0.17 λ g  × 0.23 λ g and a quad-channel diplexer operating at 0.9, 1.45, 2.1, and 2.7 GHz with a size of 0.28 λ g  × 0.23 λ g have been designed, fabricated, and measured. The electromagnetic simulated and measured results are in good agreement.