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

A 1D 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 1D electromagnetic bandgap (EBG) microstrip structure with periodic hole pattern, the design is limited to r/a ratios lower than 0.45, whereas the proposed pattern allows achieving r/a ratios higher than 0.5. It is shown that 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 1D KFEBG microstrip structure presents a ultra-wide stopband and, therefore, the proposed structure with r/a > 0.5 can be useful for the design of low-pass filters. © 2011 Wiley Periodicals, Inc.