A Note on the Isolation Performance of Nonuniform Capacitively Loaded Mushroom-Type EBG Surfaces Within a Parallel Plate Waveguide

A heuristic approach is presented to quantify the broadband isolation performance of nonuniform capacitively loaded electromagnetic bandgap (EBG) surfaces embedded inside a parallel plate waveguide (PPW). The approach is based on the effective mapping of the stop-band properties of the EBG to the attenuation factor (AF) of a homogeneous material slab. Subsequently, it is demonstrated that the electromagnetic wave propagation through the EBG-loaded PPW is equivalent to the propagation through a multilayered medium where each layer is characterized by a different AF. When these AFs are engineered so that their nonzero values spectrally overlap, a cumulative broadband attenuation effect can be obtained. Based on this interpretation, the broad bandgap properties that are characteristic of nonuniform capacitively loaded EBG surfaces are fully quantified.