A novel asymmetric defected ground structure for implementation of elliptic filters

An asymmetric defected ground structure (DGS) with respect to a microstrip line is proposed. Its unit cell consists of two square headed slots connected with a rectangular slot under microstrip line transversely. Both EM-simulation, experimental measurement and equivalent circuit responses are presented. It shows 3^rd order elliptical response whereas, conventional symmetric DGS unit like dumbbell shows Is order Butterworth response. The investigated DGS can provide better frequency response than that of the conventional dumbbell DGS. The two-cell configuration of this DGS produces 3-pole lowpass filter characteristics. The simulated, measured and equivalent circuit responses are presented for modified unit which produces 2^nd order elliptical bandstop characteristics. The two-cell structure gives deeper attenuation without appreciable change in pole frequencies. A bandpass filter is realized by coupled gap microstrip line combined with modified DGS unit.