Dual-band stepped-impedance filters for ultra-wideband applications

New ultra-wideband planar dual-band filter designs are presented. Two broad passbands with up to 48 percent fractional bandwidths are obtained by utilizing quarter- wavelength coupled-line section to create additional reflection zeros within each passband. Parallel open-end high impedance segments in stepped-impedance resonators achieve passband separation as they provide attenuation poles between the passbands. Out-of-band rejection is improved by introducing source-load coupling, which produces attenuation poles in the lower and higher rejection bands. The basic design approach is discussed. Several different dual ultra-wideband filters are proposed. Two different professional EM software packages verify the individual responses.