A New Defected Ground Structure with Elliptical Band-Reject And Band Accept Filtering Characteristics

An asymmetric defected ground structure (DGS) with respect to a microstrip line is proposed. Its unit cell consists of two square slots connected with a rectangular slot by two Z-shape thin transverse slots under microstrip line. The simulated, measured and equivalent circuit responses are presented. Unit DGS pattern under microstrip line produces two numbers of attenuation poles and two number of attenuation zeros. Thus it can be modeled by 2^nd order elliptical band-reject filter. As attenuation zeros are closed to attenuation poles, high sharpness is obtained at transition knees. The two-cell structure shows 3- pole bandstop filtering characteristics with deeper attenuation without appreciable change in pole frequencies. Unit DGS pattern under coupled gap microstrip line produces 3^rd order elliptical band-accept filtering characteristics.