Bandgap and slow/fast-wave characteristics of defected ground structures (DGSs) including left-handed features

This paper presents a T-shaped defected ground structure (DGS), which has the bandgap and slow/fast-wave characteristics including left-handed (LH) features. The closed-form expressions for the bandgap center frequency, its fractional bandwidth (BW), and radiation rate are obtained using the R,L, and C values extracted from electromagnetic (EM) simulation results for the unit-cell structure. The equivalent R,L, and C values to realize a DGS with a specific bandgap center frequency, its BW, and allowable radiation rate are also provided for use as design equations for a required unit cell with a design example. Besides, we provide the expressions for the dispersion effects of the DGS based on the equivalent circuit with adequate physical interpretations. At frequencies below and above the bandgap, it is shown to behave as an element for slow and fast waves, respectively. Some LH features when a shunt inductor is added between the two DGSs are also investigated. The measured data for the fabricated 1×4 and 1×5 one-dimensional periodic DGSs show a good agreement with those using the provided closed-form expressions and EM simulations.