Differential Mode Radiation can be reduced by
1) Reducing the magnitude of the current
2) Reducing the frequency of harmonic content of the current
3) Reducing the loop area
Common Mode Radiation can be reduced by
1) Minimising the source voltage that drives the antenna (normally ground potential)
2) Providing a large common mode impedance in series with the cable or printed track
3) Shunting the current to ground
Reduction of Common Mode (CM) and Differential Mode (DM) radiated emission
To reduce the radiated emission, we must;
1) Reduce the frequency of the signal, ie, the rise and fall time, if possible
2) Reduce the loop area – eliminate or reduce all loop area by reducing the ground loop, the signal loop by decoupling
3) Reduce the inductance of the ground plane, mutual inductance of signal and return paths. By minimising the loop area where the signal flows, we have to reduce the mutual inductance in that circuit.
4) Eliminate or reduce all radiating antenna
5) Reduce or eliminate the noise source, differential voltage, if possible. Etc.
Methods of reducing of susceptibility to radiation
1) Balance the circuit, if possible
2) Reduce all loops that can pick up the radiation by induction current flow
3) Increase/decrease the impedance of the circuit to pick up depending on whether it is near field magnetic or electric field induction.
4) Reduce or eliminate all pick up antennas
5) Apply shield and crosstalk reduction technique, etc.