Numerical and experimental methods for the comparison of radiated immunity tests in EMC sites

Electromagnetic compatibility plays a central role in today's manufacturing of electronic products. Unintended radiation by one device could produce various effects on other devices, ranging from innocuous to very dangerous. On the other hand, insufficient immunity to RF energy can cause malfunctions and interruptions in device operation. For these reasons in the past decades lots of regulatory directives were compiled to help manufacturers in producing better-performing devices in terms of electromagnetic compatibility. The ''compatibility'' of a product is verified in specific laboratories, where testing is divided in radiated immunity, radiated emissions, conducted immunity and conducted emissions. The first two kinds of tests are about disturbances propagating ''in air'', while the last two kinds are about disturbances propagating via connecting cables. Despite being of fundamental importance, neither regulations nor testing provide perfect receipts to build compatible devices; moreover testing needs to be done by means of carefully prepared experiments performed in sites whose performance is well known. Being composed by an anechoic chamber, cables, antennas, receivers and other instrumentation, a site is usually quite complex and it can be difficult to control all the involved variables. This thesis, which is focused on the radiated part of testing, proposes a novel numerical method useful to predict the performance of electrically large anechoic chambers, a topic currently subject of significant research. The method is based on the concept of \emph{equivalent models}, which allow to substitute complex objects with simpler ones. The subjects of the equivalent modeling are the antennas and the walls of the anechoic chamber, which are the most complex objects from the point of view of the geometry in this kind of simulation and which could heavily impact on its computational requirements. The aim of the proposed technique is to be a complement to the measurements usually made to evaluate the performance of anechoic sites. Since this kind of measurements is very tricky and a misplaced cable could be source of problems, using simulations measurements can be cross-checked against a numerical model, so a laboratory can be more confident about its procedures and its results. The developed theory and models would be useless without a confirmation of their functionality and applicability, so the thesis includes also an experimental part carried out at Emilab in Amaro. An extensive set of measurements was made in their anechoic chambers to compare with the predictions of the numerical models and to confirm the plausibility of the results. Finally, the numerical scheme is part of a purpose-built software that allows to simulate quite big sites on rather modest hardware