EMC Testing Services

Field uniformity

IEC 1000-4-3 requires that the radio frequency field used during immunity testing be uniform over the area shown below. To have uniformity, 12 of the 16 points shown (75%) must be within -- 0, + 6 dB of the target value (e.g. 3 V/m). In addition, each of those 12 points must be within ± 3 dB of the mean. Better uniformity increases the likelihood a product will meet the minimum requirements of the standard and improves the repeatability of the test. If a test chamber exactly met the minimum requirements of the standard, a product could be exposed to a field strength twice as large as required by the standard!

UL's chambers exhibit superior field uniformity. A typical example is shown below for vertical polarity. The required 12 points average 1.9 dB of deviation over the frequency range of 25 MHz to 1,000 MHz.

Additional Resources

• RF "ambient free" anechoic chambers
• Site attenuation