Input Impedance of Planar FP and EBG Antennas

The theoretical study of the input impedance for Fabry-Perot (FP), electromagnetic band gap (EBG) or leaky wave (LW) antennas is a real challenge from mathematical and electromagnetic modelling point of view and is very rarely addressed in the literature. In this paper, an original method will be presented to evaluate the input impedance of the EBG antennas excited by a line source or a point source. The method is based on the generalisation of the plane wave expansion of the antenna internal fields to cylindrical or spherical wave expansions. This procedure leads to simple and rigorous formulas which are very helpful for designing the EBG, FP and LW antennas and for understanding their electromagnetic behaviours.