A novel compact dual-band bandpass filter with wide stopband using stub-loaded stepped-impedance resonators is presented in this paper. The characteristics of the dual-mode resonator are investigated by using even/odd mode analysis. The center frequencies and bandwidths of the two passbands can be controlled by adjusting the geometric dimensions of the stub-loaded stepped-impedance resonators. Moreover, the filter has been implemented with five transmission zeros to improve the selectivity. A prototype of a dual-band bandpass filter centered at 3 and 4.35 GHz has been designed and fabricated. The measured bandwidths are 8.3 and 4.6%, and the corresponding insertion losses are 1.7 and 1.6 dB, respectively. A compact dual-band bandpass filter with sharp roll-off rate of 113.3/56.7/56.7/170 dB/GHz, wide stopband of 5.3 GHz, and isolation between two passbands of 25 dB is achieved. The measured results are in good agreement with the simulated ones.
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