Efficient estimation of EMI from stacked radiation sources by combining their spherical wave expansion coefficients

The objective of this study is the development of an efficient methodology, based on the spherical wave expansion theory, to evaluate the total unwanted electromagnetic radiation of multiple radiation sources starting from the knowledge of the radiation characteristic of every single source considered as isolated. The specific application domain deals with the estimation of the electromagnetic interference from stacked trays in server racks. After having computed the radiation of each isolated tray, by using the spherical expansion technique the proper expansion coefficients are calculated. They are combined in a set of new coefficients that are used to reconstruct the estimated total field from the server rack. This study discusses the proposed methodology step by step and offers practical considerations on its implementation when measured data are given as input. The adopted numerical examples show in a quantitative way, through different graphs and comparisons, the limits and the advantages of the technique. The proposed method has been shown to reliably predict the radiation from stacked trays with only a few dB of uncertainty. The examples are based on numerically computed data sets of electromagnetic emissions from trays and racks but the proposed procedure is valid also for measured data.