For interference sources to be a problem – there must be receptors. There are a great many receptors in any electrical system. These are normally referred to as wires or cables. This means that system level EMC is mostly about understanding how wires and cables become transmitting and receiving antennae and finding solutions to minimize their efficiency. At circuit and board level, we are talking about interconnecting wires and printed circuit board tracks (traces).
Since all electrical currents flow in loops, the efficiency of the wiring structure’s ability to produce emissions and/or be sensitive to interference is dependant on how we terminate the current return conductors at each interface.