Simple method to design a tri-band bandpass filter using asymmetric SIRs for GSM, WIMAX, and WLAN applications

This paper presents a simple method to design a tri-band bandpass filter (BPF) using asymmetric stepped-impedance resonators (SIRs) with one-step discontinuity.Only two SIRs are needed in the filter structure. The tri-band passband responses can be achieved by properly selecting the length ratio (u) and the impedance ratio (R) of the asymmetric SIRs. The performances can be further well tuned by the lengths of two enhanced coupling structure and gap of two asymmetric SIRs. A filter example for the applications of GSM at 1.8 GHz, WiMAX at 3.5 GHz and WLAN at 5.2 GHz was designed and fabricated. The measured results are in good agreement with the full-wave simulation results.