Radiated Emission

When testing a system for radiated emission it is very important that the system is working properly. Sometimes auxiliary equipment has to be used to let the system work as expected and you must find a way to eliminate the radiation coming from the auxiliary equipment. Most of these measurements are done in a Faraday cage to eliminate background radiation from our surroundings. An open area test site or an anechoic room is most helpful to rule out reflections that could make the measured data inaccurate.

Radiated emission measuring is the art of finding the worst case setup for the system to be tested. Important factors are the state in which the system is in or the positioning of the outgoing cables or of the system itself.

There are two types of radiation that can be measured: the electrical- and magnetic field. The electrical field is measured in a frequency range of 9kHz - 40GHz. This measurement is done with an antenna situated approx. 1, 3 or 10 meters from the system to be tested (Equipment Under Test, EUT). The magnetic field is measured in a much lower frequency range because a magnetic field of a higher frequency changes into an electric field within several inches from the EUT. The magnetic antenna is placed at 0 cm or at distances up to 10 meters in distance of the EUT. The frequency range is between 5Hz and 100MHz (Higher is also possible but not mandatory in accordance with the harmonized standards).