Radiated emissions from printed circuit board traces including the effect of vias, as a function of source, termination and board characteristics

The radiation from a printed circuit board (PCB) trace (microstrip) is analyzed including end effects. The end effects are due to the “vias” which connect the trace to the circuit board ground. The PCB trace currents are calculated from closed-form transmission line equations which includes dielectric effects of the board. The board ground plane is assumed to be infinite. Electric field magnitudes are then found from these currents using a free space Green´s function ignoring the board dielectric. This is compared with full-wave method of moments (MoM) analysis for finite size ground planes. The effect of ground plane size variations is noted. The worst case electric field magnitude is calculated from 50 to 2000 MHz at numerous points on a sphere with a 3-meter radius. The via radiation is isolated from the PCB trace radiation to observe the relative magnitudes. The motivation for this work is twofold. We wish to quantify the magnitude of radiation, which occurs from differential mode currents flowing through horizontal components such as PCB traces and vertical components such as vias, and package leads. Also, we wish to see how this radiation is affected by source, termination and board characteristics