Non-uniform currents on vias and their effects in a parallel-plate environment

This paper discusses the generation of non-uniform currents on vias and their impact on the field distribution at the via antipads as well as on the excitation of cavity modes supported by adjacent reference planes. It is shown that the influence of non-uniform currents can be relevant at frequencies above 10 GHz for typical printed circuit board dimensions. The contour integral method is applied to extract the current nonuniformity due to vias in close proximity. An identification of modes is carried out via a discrete Fourier transform. The energy content of the higher modes increases with frequency and via size. It is demonstrated by means of full-wave simulations that non-uniform via currents can lead to anisotropic electromagnetic fields in the antipad region and to the excitation of anisotropic cavity modes.