The dual-band bandpass filters using doubly parallel-coupled sirs with multiple zeros for WLAN applications

Two dual-band bandpass niters (BPFs) based on the dou bly parallel-coupled stepped impedance resonators (SIRs) structures have been proposed in this paper. The coupled-SIRs with/without open-stub-loads are introduced in the filter design. The dual-band filters exhibit ing multiple zeros design operate at 2.45/5.2-GHz for the WLAN appli cations. Two three-staged filters composed of four SIRs have been pro posed with the tapped-line adapted in the I/O sections. A five-staged fil ter is constructed based on the same design principle to achieve a better band-rejection. The proposed filters have the advantages of a much wider bandwidth in both the passbands without sacrificing the passband's inser tion loss and passband flatness. The design procedure for a conventional parallel-coupled microstrip lines model is still suitable to design the pro posed filters. The proposed filters have achieved almost twice the band width of a conventional parallel-coupled lines configuration under the same design parameters. The experiments have been conducted to verify filter performance. Measured results are in good agreement with the full-wave simulation results.