System Level Electromagnetic Compatibility Remedy Using Absorbing Frequency Selective Surfaces

To mitigate unwanted electromagnetic emissions from a digital system enclosed in a metal box with ventilation slots at 8 GHz, a customized absorber is developed using the Frequency Selective Surface (FSS) design concept. The low profile FSS is composed of 2D arrays of square patches of a resistive material incorporated in two consecutive layers of a PCB stack-up. The designed FSS covers the inner top wall of the enclosure box. Analytical derivations and full-wave simulations demonstrate that the surface input impedance of FSS at 8 GHz is matched to the intrinsic impedance of the plane waves emitted from the digital system thus providing more than 6 dB reduction in radiated emissions when FSS is present. The FSS structure is fabricated and a test set-up is created to measure the emissions from a prototyped system board with an array of intentional radiators operating at 8 GHz. Lab measurement results also confirm more than 5 dB reduction in radiated emissions at 8 GHz for the worst case emission scenario.