IEEE 299 and 299.1 on Measuring the Shielding Effectiveness of Enclosures
IEEE 299 is titled “Standard Method for Measuring the Effectiveness of Electromagnetic Shielding Enclosures” and is by far the most widely used IEEE standard sponsored by the EMC Society. IEEE 299.1 is the “Standard Method for Measuring the Shielding Effectiveness of Enclosures and Boxes Having All Dimensions between 0.1 m and 2 m”. It is also widely accessed. While both of these standards are considered currently “inactive”, you can purchase 299 (here) and 299.1 (here) from the IEEE.
IEEE 299 is a relatively straightforward standard, with 39 pages of technical content of which 13 are found in five informative annexes. IEEE 299.1 is rather more complex, since it deals with situations where enclosure dimensions are small compared to the wavelengths of the RF fields and frequencies of interest. The copy I have has 44 pages in the main document, plus another 38 pages in 12 informative annexes.
Dealing with enclosures where the smallest dimension is 2 m or greater, IEEE 299 defines test methods from 9 kHz - 18 GHz, extendable down to 50 Hz and up to 100 GHz. The table below shows the recommended antennas for different frequency ranges.
Depending on the frequency range, the measurand might be voltage, H field, E field, or power. After that, shielding effectiveness can be calculated in a straightforward way, comparing the value without the enclosure (Value1) to the value with the enclosure (Value2):
[linear values] SE = 20 log10 (Value1/Value2) (or 10 * log10 when comparing power)
Or
[dB values] SE = Value1 - Value2
The measurements involved aren’t trivial, but with enough space to place equipment the procedures are relatively simple.
IEEE 299.1 has a harder job, since the smaller dimensions seriously constrain test equipment and configurations. It officially covers the same frequency range as 299. The standard divides itself into two sections, one covering 0.75 - 2 m and the other 0.1 - 0.75 m. At this point, testing within a reverb chamber becomes a much more attractive option than in IEEE 299, and the standard spends a lot of time on those methods (see also IEC 61000-4-21). Data collected this way takes a little more math to interpret correctly, due to the statistical nature of reverb chamber measurements. The standard as currently written feels somewhat incomplete and refers to continuing research in the area of measurements of physically and electrically small enclosures.
Both of these standards have been approved to move forward with renewal by the EMC Society and will be moving to IEEE Standards Association approval in the Fall of 2024. After that approval comes through a working group will be formed under the leadership of Dr. Davy Pissoort of KU Leuven. The expectation is that IEEE 299 will be renewed with only minor updates to the technical content, where 299.1 will require more extensive revisions. If you are interested in being involved in this effort, please contact me at standards@emcunited.com and I can put you in touch with Dr. Pissoort.