On the effectiveness of decoupling capacitors in reducing EM radiation from PCBs

The effectiveness of using decoupling capacitors (decaps) between power and ground planes in a typical PC or workstation printed circuit board (PCB) is studied from an EMC point of view. By examining the radiation from the board, the effects of the total number of decaps, the placement of decaps and lead inductances are investigated. The novelty of our studies is that we focus directly on EM radiation as opposed to the more traditional investigation of decaps by only examining their equivalent impedances.