Measured average absorption cross-sections of printed circuit boards from 2 to 20 GHz

The contents of an equipment enclosure, particularly printed circuit boards (PCBs), affect the enclosure’s shielding performance. At high frequencies this absorption can be quantified using the angle of arrival and polarization averaged absorption cross-section (ACS). However, there is no available data on the high-frequency absorption characteristics of modern PCBs. In this study we apply a reverberation chamber to the determination of the average ACS of a large number of printed circuit boards taken from contemporary information and communication technology (ICT) equipment to provide a unique and comprehensive data-set. The ACS was found to range from 4×10-4 –10-2 m2 from 2-20 GHz and different classes of PCB could be identified according to their surface characteristics. The "shadowing effect" of densely packed PCBs was also quantified for a subset of the PCBs. It was found that the ACS of a PCB in the stack was reduced by 20% - 40% compared to its value when isolated. By way of a review of the general power balance analysis of an electrically large populated equipment enclosure in an external environment we show how the acquired data will be useful for future qualification methodologies for ICT enclosures and PCBs.