Evolution of the equivalent currents in high-frequency diffraction

Discusses the equivalent current method for high frequency scattering. In every equivalent current formulations, the background is that of finding the local, incremental field contribution to be distributed and then integrated along specific lines on the actual object. Also, appropriate cylindrical canonical configurations are used to locally approximate the actual shape. Different procedures have been used to find the relevant local incremental contributions. In this paper those procedures are briefly summarized to show the development of the equivalent currents over the last three decades that led to the most recent achievements of this method. Finally a rather general procedure is discussed to treat cylindrical canonical problems for an elementary source illumination and arbitrary observation aspects. In particular, it is shown that the spectral integral formulation of the exact solution may also be represented as a spatial integral convolution along the axis of the cylinder. Then, its integrand is directly used to define the relevant incremental field contribution.