Measurement of Transmission through Printed Circuit Boards : Application to Enclosure Shielding

It is important when considering the shielding effectiveness (SE) of an enclosure to take into account any contents the enclosure may have. Contents such as printed circuit boards (PCBs) will absorb electromagnetic energy and so affect the SE of the enclosure. Previously, it has been shown that the absorption cross section (ACS) of PCBs and the transmission cross section of apertures can be used in the power balance method to predict the SE of simple enclosures. However, in a more realistic enclosure, multiple cavities may be formed by PCBs that cover a large proportion of the enclosure cross section. In this case, the transmission through the PCBs, as well as through the apertures, needs to be considered. In this paper, we describe measuring the transmission through a PCB using a method normally used to measure the SE of planar samples. This measurement is quick and efficient to carry out, as no special preparation of the PCB is required. The results are shown from a selection of PCBs and limitations of the measurement discussed. The data collected can be used in power balance or computational modelling to allow engineers to determine a more accurate estimate of enclosure SE when designing electronic systems.