Radiated coupling

Definition

The disturber and the victim are coupled by a medium (e.g. air). The level of disturbance depends on the power of the radiating source and the effectiveness of the emitting and receiving antenna. An electromagnetic field comprises both an electrical field and a magnetic field. The two fields are correlated. It is possible to analyse separately the electrical and magnetic components.

The electrical field (E field) and the magnetic field (H field) are coupled in wiring systems via the wires and loops (see Fig. R37).

Fig. R37 – Definition of radiated coupling

When a cable is subjected to a variable electrical field, a current is generated in the cable. This phenomenon is called field-to-cable coupling.

Similarly, when a variable magnetic field flows through a loop, it creates a counter electromotive force that produces a voltage between the two ends of the loop. This phenomenon is called field-to-loop coupling.

Examples

(see Fig. R38)

• Radio-transmission equipment (walkie-talkies, radio and TV transmitters, mobile services)
• Radar
• Automobile ignition systems
• Arc-welding machines
• Induction furnaces
• Power switching systems
• Electrostatic discharges (ESD)
• Lighting

Fig. R38 – Examples of radiated coupling

Counter-measures

To minimise the effects of radiated coupling, the measures below are required.

For field-to-cable coupling

• Reduce the antenna effect of the victim by reducing the height (h) of the cable with respect to the ground referencing plane
• Place the cable in an uninterrupted, bonded metal cableway (tube, trunking, cable tray)
• Use shielded cables that are correctly installed and bonded
• Add PECs
• Place filters or ferrite rings on the victim cable

For field-to-loop coupling

• Reduce the surface of the victim loop by reducing the height (h) and the length of the cable. Use the solutions for field-to-cable coupling. Use the Faraday cage principle.

Radiated coupling can be eliminated using the Faraday cage principle. A possible solution is a shielded cable with both ends of the shielding connected to the metal case of the device. The exposed conductive parts must be bonded to enhance effectiveness at high frequencies.

Radiated coupling decreases with the distance and when symmetrical transmission links are used.