Automated near Field Spatial Mapping for Multilayer Ground Split Noise Detection
Automated near field spatial mapping identifies hidden split-plane return current loops and isolates board-level electromagnetic noise sources before EMI certification.
Planar Radiated Emissions
Field Radiation
Evaluating the energy escaping from the edges or surfaces of a flat circuit structure provides a metric for electromagnetic containment. Designers monitor planar radiated emissions to ensure that the board does not exceed the limits set by regulatory bodies. Radiation of this type is often the result of resonant structures formed by the planes themselves.
Structural Cause
The gap between power and ground planes can act as a patch antenna or a parallel plate waveguide if not properly terminated. In this situation, planar radiated emissions are generated when high frequency noise from switching components propagates to the edge of the board. The energy is then launched into free space, potentially interfering with other electronics.
Thin substrates can increase the capacitance between planes but may also change the frequency of these resonances.
Suppression Method
Adding a row of stitching vias along the perimeter of the board helps to contain the energy within the stackup. These vias act as a Faraday cage that restricts planar radiated emissions from leaking out of the edges. Designers also use edge plating or specialized absorbing materials to further reduce the radiation.
Proper decoupling at the source of the noise remains the most effective way to prevent the energy from reaching the edges.