Electromagnetic Dissipation
Dissipation of electromagnetic energy from printed circuit trace paths reduces the signal power delivered to load terminations. High-speed transmission lines experiencing radiative loss shed high-frequency signal components into the surrounding dielectric and free space. This attenuation behaves as an added insertion loss that degrades the integrity of digital signals.
The phenomena becomes increasingly pronounced at frequencies exceeding ten gigahertz where traces behave as unintentional antennas.
Circuit Design
Trace geometry and substrate selection dictate the level of emissions generated by high-speed printed circuits. Microstrip lines on open outer layers suffer higher radiation levels than striplines embedded between protective ground planes. Designers minimize these emissions by using tightly coupled differential pairs that allow opposing electromagnetic fields to cancel each other out.
Any layout discontinuities, such as vias or acute angle bends, alter the local impedance and force return currents to take wider paths, which escalates radiative emissions. Controlling trace width and maintaining solid reference planes are therefore standard practices in high-frequency circuit layouts.
Shielding Compliance
Regulatory testing ensures that emitted energy remains below established limits for electromagnetic compatibility. When radiative loss causes an assembly to exceed emission standards, the board fails certification, requiring redesign or the addition of metal shields. Applying localized shielding cans over high-power components prevents the escaped energy from interfering with nearby circuits.
