Application of Stepped-Impedance Technique for Bandwidth Control of Dual-Band Filters

This paper demonstrates application of the popular stepped-impedance technique to control the bandwidths of dual-band filters independently. Unlike previous dual-band stepped-impedance filters, the role of the stepped-impedance technique is to control the bandwidths of the two bands rather than to provide dual-band performance. The exact relationship between stepped-impedance ratios and the ratio of the two absolute bandwidths is obtained through rigorous analysis. Moreover, since the proposed filters can be synthesized with popular transmission lines and coupled lines that are very-well characterized, time-consuming full-wave simulation can be minimized. Along with the complete set of design equations, experimental results for transmission-line and coupled-line dual-band filters are provided that verify the proposed approach.