![]() One way to mitigate this problem is to create a “picket fence” of vias around the perimeter of the PCB, as shown in Figure 2. ![]() ![]() When the wave meets the PCB edge, the two reference planes form a slot antenna and will radiate noise with the potential to generate electromagnetic interference (EMI) to nearby equipment.įigure1 Simplified cross-section schematic of via passing through two adjacent plane layers showing edge emissions due to via induced EM fields between plane cavities.Įmissions can also occur when fringe fields from high frequency traces are routed too close to the edge of the PCB, or when unintentional currents are generated by power and ground noise, due to poor decoupling practices. It is guided by the respective planes much like a water ripple will propagate radially away from a rain drop hitting a puddle of water. When a current carrying via passes through two or more reference planes, an EM wave propagates radially away from the via within the cavity, as shown in Figure 1. It is a well-known fact that electromagnetic radiation can be emitted from the edges of printed circuit boards (PCBs). ![]()
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