Folded Compact Ultra-Wideband Stepped-Impedance Resonator Filters

New ultra-wideband stepped-impedance resonator configurations are presented which, in cascaded and folded forms, are well suited for compact small-size filter applications. Compared to similar structures known hitherto, improved stopband performance is obtained by structural folding and source-load coupling. A variety of different filter configurations is presented with bandwidths up to 105 percent covering the 3.1-10.6 GHz range. Excellent stopband performance is obtained up to 16 GHz. The filters are designed for standard microstrip applications on commonly used substrate materials, and their responses are verified by different commercial electromagnetic software packages.