A simple method and structure to design a dual-band filter by using λ/4 stepped impedance resonators (SIRs) is presented in this paper. This filter has enhanced performance, including a good rolloff in the stopband and good insertion-loss response. The structure is compact and easy to fabricate. The circuit is investigated with the even-odd mode theory to prove the existence of transmission zeros. The dual-band response is analyzed by using SIR theory and the parallel-coupled line theory. Based on the proposed filter topology, two dual-band filters center operating frequency at 2.4 GHz and 5.2 GHz respectively with different configurations have been designed and one of them was tested, which validates the diversity of the filter configuration. Experimental results show that the measured and simulated performances are in good agreement. The overall area of the fabricated filter is 12mm * 12 mm.
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