Analysis and synthesis of defected ground structures (DGS) using transmission line theory

This paper presents a T-shaped DGS which has a wider range of gap capacitance due to two adjacent conductor strips protruded into the dumbbell-shaped DGS. In addition, this structure is completely analyzed and its design equations are provided using transmission line theory. The expressions for the 3dB fractional bandwidth about the bandgap center frequency and radiation rate are presented in closed-form expressions using the R, L, and C values extracted from EM simulation for the structure. The equivalent R, L, and C values to realize a DGS with specific bandgap center frequency, its bandwidth, and radiation rate are also obtained for use as design equations. The equations for the analysis and synthesis of a DGS facilitate the design procedure in a much more controlled manner. The ID periodic DGS with four unit cells is fabricated and its measured S-parameters are shown to be in good agreement with those based on transmission line theory and EM simulation.