Comparison of planar fractal filters on defected ground substrate

The paper discusses approaches to the reduction of dimensions of planar filters (microstrip ones and coplanar ones). Filter dimensions are reduced by applying the fractal theory to the geometry of a filter, and by the defecting of the ground plane of a filter. An optimum combination of both approaches enables us to reach smaller dimensions of planar filters and protect other parameters. In order to demonstrate advantages of the fractal defected ground approach, we review the designs of existing low-pass filters with defected ground structures (DGS). Results produced by simulations of these filters are compared with results of simulations of a novel fractal DGS filter. The investigated filters are manufactured and measured.