3.1 Conducted emission - Radiated emission

Cables connected to a device carry unwanted transient signals and other disturbances to other devices. This is the general conducted emission definition [55]. The conducted emissions are measured with voltage and current measurements on the cables. Such measurement methods are standardized, for instance, for automotive appliances in CPSPR25 [56]. The voltage measurement method measures the conducted emissions only on the power and eventually the ground cable on a LISN (Line Interface Simulation Network). However, that is of utmost relevance, because the disturbances on the power supply are distributed to other devices by the power delivery network. The current measurement method with a coupling coil measures the common mode current on a multi-wire cable harness. The measured conducted emissions are initiated by galvanic coupling, electric and magnetic near field coupling, and even from radiated far fields. Transient signals and disturbances on the cables also cause radiated emission. Thus, every PCB emission mechanism that causes radiated emissions from cables attached to the PCB is also relevant for the conducted emissions. The following description of emission mechanisms from the PCB, therefore does not further distinguish between radiated and conducted emission mechanisms.

All radiated and conducted emission measurement methods have different measurement sensitivities for different emission frequency ranges and different emission coupling mechanisms. This is the main reason for the application of different methods for device EMC compliance measurements.

Emission from PCBs can be classified based on the following two main mechanisms:

• Direct radiation from PCB sources.
  • Differential mode signals on the PCB and on attached cables.
• Emissions through galvanic coupling, electric and magnetic near field coupling to
  cables, long nets, and mechanical structures, which can be interpreted as antennas.
  • Common mode coupling from the differential mode signals.
  • Unintentional, parasitic signals on the PCB and on attached cables.

C. Poschalko: The Simulation of Emission from Printed Circuit Boards under a Metallic Cover