The dual-band bandpass filter (BPFs) based on the doubly parallel-coupled stepped impedance resonators (SIRs) structures were proposed in this document.  The proposed filter has the advantages of a much wider bandwidth in both the passbands without sacrificing the passband’s insertion loss and passband flatness.  The interlaced circuit layout for the doubly-parallel-coupled SIR filter design allow this circuit to have multiple transmission zeros which are used to enhance the filter’s signal selectivity and the stopband performance.

The dual-band bandpass filter (BPFs) based on the doubly parallel-coupled stepped impedance resonators (SIRs) structures were proposed in this document. The coupled-SIRs with open-stub-loads were introduced in the filter design. The dual-band filters exhibiting multiple zeros design operate at 2.45/5.5 GHz for the WLAN applications. Two three-staged filters composed of four SIRs were proposed with the tapped-line adapted in the I/O sections.  The proposed filter has 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 interlaced circuit layout for the doubly-parallel-coupled SIR filter design allow this circuit to have multiple transmission zeros which are used to enhance the filter’s signal selectivity and the stopband performance.  Also the interlaced coupling structure of this filter design provides a compact circuit layout to save the circuit size.  The fabrication of this circuit is based on the printed circuit board technology which allows itself to be built by a very low cost and to be massive produced without any difficulty. The PCB technology also grants the circuit the advantages of low cost, low profile, easy of mass production.  In conclusion, we have the following:
1.The interlaced coupling design allows the filter to have two alternative signal routes for introducing transmission zeros by the passband edges, which effectively enhances the filter’s signal selectivity and the stopband’s spurious responses.
2.The planar structure and usage of printed circuit board technology of this circuit design has granted itself the advantages of low cost, low profile, and easy of mass production.
3.The transmission zeros can be easily determined by the overlapping dimensions of the coupling edges
4.This filter design is very unique which is rarely seen in the literature and has been documented by a famous international journal.

需要無線通訊或是無線傳送與接收的場合越來越多，未來市場可期。