Near- and far-field characterization of perforated screens: theoretical and experimental study of proposed definitions for the shielding performance

The shielding performance of a periodically perforated plane shield is investigated, both theoretically and experimentally. Attention is focused upon a clear formulation of the near-field shielding effectiveness of the perforated screen. It will be shown that such a near-field analysis often is mandatory because the classical far-field definitions drastically overestimate the near-field shielding performance. Moreover, the influence of some relevant parameters (such as frequency, shield distance and loop radius) upon the near-field shielding effectiveness is analyzed