Miniaturized dual-band bandpass filter using quarter-wavelength stepped-impedance resonators

In this paper, we present a novel dual-band miniaturized bandpass filter. The quarter-wavelength stepped impedance resonators are used to generate dual-band response. For circuit size reduction, the resonators are folded and coupled by a parallel microstrip line. Four transmission zeros are created near the passband, resulting high selectivity. The area of the filter is only 6.7 mm × 7.7 mm (0.098λ_g ×0.11λ_g), where λ_g is the guided wavelength at the operating frequency of 2.35GHz. For demonstration, a dual-band BPF have been implemented. Comparisons of the measured and simulated results are presented to verify the theoretical predications.