A novel bandpass filter with sharp attenuations and wide stopband developed through the combined use of composite resonators and stepped impedance resonators

In this paper, a novel four-pole microstrip bandpass filter (BPF) with sharp attenuations and wide stopband is developed through a combined use of composite resonators and stepped impedance resonators (SIRs). By using a full-wave electromagnetic simulator, the filter is designed with a midband frequency of 1.0 GHz and a fractional bandwidth of 2%. The measured frequency response of the filter agrees well with the simulated result, and exhibits transmission zeros at about 0.9, 1.1, and 1.15GHz, respectively. The transition from the passband to the stopband is thereby sharp and deep. The stopband with attenuations larger than 30dB extends up to approximately 6.7GHz, which is 6.7 times the midband frequency of the filter.