Compact quasi-elliptic function filter based on defected ground structure

A novel defected ground structure (DGS) is investigated for filter applications. With this structure, the basic resonant element exhibits the quasi-elliptic function responses. A new equivalent lumped L–C circuit model is presented and its corresponding L–C parameters are extracted by using parametric relationships, which has quasi-elliptic characteristics. The theoretical analysis for the effect of different design parameters has been carried out, which provides effective guidance in designing DGS. The performance of the new filter is also compared with the characteristic of the dumb-bell DGS filter to highlight the advantages of the proposed DGS. Based on the equivalent circuit model, a three-pole quasi-elliptic lowpass filter (LPF), using two DGS units cascaded, is optimally designed and implemented; experimental results show good agreement with theoretical ones.