Suppression of Multilayer Plane Cavity Resonances Using Peripheral via Arrays
Peripheral via arrays eliminate multilayer PCB cavity resonances by constructing an electromagnetic fence that suppresses high-frequency edge radiation.
Edge Radiation Suppression
Grounding Configuration
High frequency emissions escaping from the periphery of a printed circuit board require containment to prevent electromagnetic interference with nearby signal paths. This edge radiation suppression technique utilizes copper pour or stitched via fences along the board perimeter to force return currents away from the board edge. Designers implement these barriers to contain electrical noise within the substrate boundaries.
Signal Containment
Proper implementation involves placing a row of vias connected to an internal ground plane at a distance from the board profile not exceeding one tenth of the wavelength of the highest frequency component. These vias define a low impedance path that directs stray fields back into the reference plane rather than allowing field lines to terminate at the cut edge of the dielectric material. Effective layout practice mandates that such via structures follow the contour of the internal copper layers to maintain a consistent gap.
Engineers verify the performance of this containment method using near field probes during electromagnetic compatibility compliance testing.
Boundary Control
Shielding effectiveness depends upon the spacing between these perimeter vias relative to the signal rise time. Vias placed too far apart allow electromagnetic leakage to occur between individual holes. Close spacing creates a continuous wall that effectively mimics a solid metallic sheet and eliminates the slot antenna effect along the board edge.
Proper alignment reduces the probability of radiated emissions failing regulatory standards.