Miniaturized dual-band microstrip bandpass filter with wide stopband

This paper presents a compact, wide-stopband, and dual-band microstrip bandpass filter using stub-loaded stepped-impedance resonators (SLSIRs). The resonators consist of three stepped-impedance sections. By adjusting the parameters of the resonator, one can control the frequencies of the resonant modes as well as those of the transmission zeros. When the transmission zero frequency is close to the spurious resonant mode frequency, one can have a wide-stopband bandpass filter without any external circuits or increasing the resonator for suppressing the spurious passbands. To validate the design concept, a dual-band bandpass filter is designed, fabricated, and tested.