Modeling of Modified Split-Ring Type Defected Ground Structure and Its Application as Bandstop Filter

Abstract

The shape of a popular split-ring defected ground structure (DGS) is modified by selecting different width of the sides with respect to microstrip line. The frequency characteristics of proposed DGS unit show an attenuation zero close to the attenuation pole frequency. The unit cell is modeled by 3rd order elliptical lowpass filter and an equivalent circuit is presented accordingly. For proposed DGS, both pole and zero frequencies are obtained at lower values compared to split-ring DGS unit with uniform width. The variation of the width of the sides, parallel to microstrip line influences pole frequency. Two DGS cells with different pole frequencies cascaded under High-Low microstrip line realize a sharp and deep bandstop filter. Three-cascaded cells underneath a highlow impedance microstrip line produce sharper and wider bandstop filter characteristics.