The Dual-Band Bandpass Filters Using Doubly Parallel-Coupled SIRs with Multiple Zeros for WLAN Applications

Min-Hua HO  Hao-Hung HO  Chen-Mao RAO  

IEICE TRANSACTIONS on Electronics   Vol.E91-C   No.6   pp.949-955
Publication Date: 2008/06/01
Online ISSN: 1745-1353
DOI: 10.1093/ietele/e91-c.6.949
Print ISSN: 0916-8516
Type of Manuscript: PAPER
Category: Microwaves, Millimeter-Waves
doubly parallel-coupling,  multiple zeros assignment,  dual-band BPF,  WLAN,  

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Two dual-band bandpass filters (BPFs) based on the doubly 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 exhibiting multiple zeros design operate at 2.45/5.2-GHz for the WLAN applications. Two three-staged filters composed of four SIRs have been proposed with the tapped-line adapted in the I/O sections. A five-staged filter 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 insertion loss and passband flatness. The design procedure for a conventional parallel-coupled microstrip lines model is still suitable to design the proposed filters. The proposed filters have achieved almost twice the bandwidth 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.