Design of dual-band microstrip filter using SIR

Two novel dual-band microstrip filters using lambda(g)/2 Stepped-Impedance-Resonator(SIR) resonators are proposed in this paper. The prominent feature of the SIR filter is that the spurious response can be controlled by the impedance ratio R-z and the length ratio of the resonator. Simulated results show that the prototype of the dual-band filter1 achieves insertion loss of 0.4dB and 0.5dB, return loss of 23dB and 23.7dB, and fractional bandwidth of 9.8% and 8.2% at 2.4GHz and 5.2GHz, respectively. And the filter2 achieves insertion loss of 1.6dB and 2.8dB, and fractional bandwidth of 6.2% and 5.1% at 2.4GHz and 5.2GHz, respectively, and the isolation between two passband is well. The proposed dual-band band pass filters are designed and fabricated. A good agreement is achieved between measured and simulated results.