New techniques for reducing printed circuit board common-mode radiation

A multilayer PCB (printed circuit board) with a solid ground-plane produced radiated emissions similar to a dipole antenna. These emissions were reduced by decreasing the distance between the signal trace and the ground plane, by providing additional low-impedance paths for the signal current, and by placing an image plane above the PCB and connecting it to the ground plane around its periphery. Adding cables to the multilayer PCB increased the emissions at some frequencies. These emissions were also reduced by reducing the ground plane noise voltage