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.
Guided Wavelength
Wave Propagation
Electromagnetic energy traveling along a printed circuit transmission line occupies a physical space determined by the surrounding materials. This boundary condition modifies the velocity of the signal, establishing a specific guided wavelength that is shorter than the wavelength in free space. The signal speed depends directly on the effective dielectric constant of the laminate.
Medium Calculation
Calculating physical dimensions for microstrip or stripline structures requires scaling the operating frequency to the propagation medium. A designer determines the guided wavelength by dividing the speed of light in a vacuum by the product of the operating frequency and the square root of the effective relative permittivity. Fabricators rely on these calculated dimensions to build printed antennas and high-frequency couplers.
High-frequency boards require precise dielectric control to ensure that these distributed elements function at the targeted frequency.
Trace Geometry
Line widths and lengths designed for high-frequency circuits must scale with the signal frequency to avoid unwanted resonance. When trace dimensions approach a quarter of the guided wavelength, the conductor begins to behave as a transmission line rather than a simple connection. Stub traces or unterminated routing branches can act as short circuits or open circuits at these frequencies, causing severe reflection and signal loss.
Precision lithography and controlled etching maintain the uniform trace widths required to prevent changes in wave impedance. Incorporating tight tolerance limits on dielectric thickness during fabrication ensures that the manufactured board matches the simulated electrical behavior.
Perimeter Stitching via Pitch Selection for Circuit Board Shielding
Perimeter via pitch selection requires matching ground via spacing to less than one-twentieth of target frequency wavelength while verifying barrel plating thickness.