Capacitively Loaded Mushroom-Type EBG
This section presents a compact methodology that allows wideband or multiband surface wave suppression through capacitive loading of a mushroom-type EBG. The capacitive loading is applied across the gaps defined between the patches of neighboring unit cells. The documented analysis begins by giving first the theoretical justification behind the choice of this particular loading scheme. Once the necessary theoretical basis has been established, the practical and computational aspects of the problem are discussed.
As mentioned previously, the objective in the proposed design methodology is to determine the loading capacitor combination that yields some desired isolation performance. Obviously, if one attempts to determine the necessary capacitor values through repeated 3D full-wave simulations, the problem becomes computationally intractable even for an EBG structure with a moderate number of unit cells. The beauty of the proposed methodology is that it exploits the fact that the EBG configuration under study can be conveniently represented as a multiport microwave device and thus it can be effectively described in terms of an 5-matrix. As a result, its analysis does not require computationally intensive 3D full-wave simulations but rather simple circuit-type calculations that drastically reduce the simulation/design time. In addition, the design time is further accelerated by integrating the aforementioned circuit-based analysis of the EBG into an optimization procedure, which can be utilized to determine the appropriate values of the loaded lumped elements based on some targeted design criteria.