1D Koch fractal electromagnetic bandgap microstrip structures with r /a ratios higher than 0.5

A 1-D Koch fractal electromagnetic bandgap (KFEBG) microstrip structure is proposed. It is conceived by replacing the conventional holes etched in the ground plane of a microstrip line by level-1 Koch fractal cell geometries, which have been obtained from a hexagonal shape. In the case of the conventional 1-D EBG microstrip structure with periodic hole pattern, the design is limited to r / a ratios lower than 0.45, while the proposed pattern allows achieving r / a ratios higher than 0.5. It is shown the conventional EBG and KFEBG microstrip structures behave as a stopband filter as r / a ≤ 0.45 . However, for r/ a = 0.55, the measurements have confirmed that the 1-D KFEBG microstrip structure presents a ultrawide stopband and, therefore, the proposed structure with r / a > 0.5 can be useful for the design of low-pass filters.