A lumped element equivalent circuit of E-shape microstrip structure for UWB filter design

Recently the E-shape microstrip structure was proposed in order to develop miniaturized ultra-wide band (UWB) bandpass filters. In spite of its attractive features, no thorough analysis of this structure is available in the literature. In this paper, the E-shape microstrip structure with grounded center conductor is analyzed and, for the first time, an approximate equivalent circuit is proposed for its behavior. Based on the equivalent circuit, two compact second-order microwave filters with UWB responses are designed, fabricated and measured. The approximate dimensions of the filter covering the whole UWB is about 3 mm × 1.5 mm × 0.4 mm. The theoretical and measured responses of the filters show good agreements.