Microstrip Dual-narrowband Bandpass Filter with Independent Passbands

In this article, a novel compact microstrip dual-narrowband bandpass filter (DNBPF) is presented with wide and high rejection levels in the stopbands. The location of each passband is independently controllable/tunable/selectable. The filter structure is made up of three-coupled-asymmetrical transmission lines, open-ended stubs and direct-transmission lines. Employing these lines can generate two narrowband passband filters. By combining these passband filters, the proposed DNBPF is configured. The proposed DNBPF is investigated. The center frequency of the first and second passband are 5.745 and 6.489 GHz, respectively. Also, the proposed DNBPF presents the fractional 3-dB bandwidth of the first and second passband 3.66 and 2.33%, respectively. It has the flattest group delay variations in comparison with previously published papers due to the design freedom. |S12|< -30 dB is from 10.1 to 19.25 GHz in the last stopband. The occupied area of the proposed DNBPF is $$0.225\lambda_{g} \times 0.11\lambda_{g}$$ , where $$\lambda_{g}$$ is the guided wavelength at the first center frequency.