The proposed open-loop dumbbell-shaped bandpass DGS unit is shown in Fig. 1(a). It has a pair of end-coupled microstrip lines with equal-length on the top and a dumbbellshaped outline symmetrically etched in the ground plane. The etched pattern consists of two identical square-loops having open-loop edge length (L) together with open-ends (g) and a slot-line (named dumbbell-arm) connected between them. In this configuration, the dumbbell-arm is aligned with themicrostrip line on the top. In contrast to the conventional dumbbell DGS configurations [1-4], this DGS unit has a 90- degree difference in the geometrical orientation.
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