A mixed model for the determination of normalized site attenuation in OATS

Normalized site attenuation (NSA) has become the standard method for determining the adequacy of open area test sites (OATS) to perform electromagnetic interference (EMI) emission and immunity measurements. Practical experience and measurement data have shown to great extent that in cases where the hypothesis of an infinitely conducting ground plane cannot be fulfilled, the models, up to the present, are not exact. The objective of this paper is to obtain a simple but more accurate model for the measurements of several equipment under test (EUT). The model introduced is based on complex image theory, and also accounts for the near field correction factor and the contribution of Norton surface wave component (vertical electric dipoles cases, only) in a simple algebraic model. Four well-known models are compared to the one presently introduced leading to some useful results, such as the accuracy of the proposed model.