Application of two concentric rectangular split ring defected ground structure for designing a quasi-elliptic low pass filter

The shape of a popular split-ring defected ground structure (DGS) is modified by etching two concentric split-ring defective pattern which have different size and inverse split direction in the ground plane underneath a microstrip line. The frequency characteristics of proposed DGS unit show an attenuation zero close to the attenuation pole frequency. As a result, better transition sharpness, lower passband insertion loss and broader stopband are observed compares to dumbbell DGS. An equivalent lumped L-C network is proposed to model the introduced DGS unit and corresponding L-C parameters are extracted. A 3rd order quasi-elliptic lowpass filter is designed by cascading two investigated DGS units under High-Low impedance microstrip line.