There are plenty of ways of testing units for radiated immunity (or radiated susceptibility, for the aerospace/defense world). As of MIL-STD-461 Rev E, that document allows RS103 to be tested in a reverb chamber as an alternative to the more traditional absorber-lined semi-anechoic chamber (ALSE) test setup. In the automotive industry, ISO 11452-11 describes a reverb test method for components, and this has flowed down to some OEM-specific requirements, like Ford’s RI114. If you’re worried that testing to the 3 V/m or 10 V/m immunity levels of IEC 61000-4-3 is still missing some real-world vulnerabilities of your hardware, you may want to consider testing per IEC 61000-4-21.
There are significant advantages to testing in a reverb chamber. One major advantage is that instead of illuminating specific faces of the unit under test (UUT), due to the chamber reflections, a UUT is being hit from multiple directions. This is much more representative of real-world conditions, where you rarely know exactly where a threat radiator might be relative to your unit. RS103 only tests in one orientation (and even though testers are supposed to establish the “worst case” orientation, “worst case” at one frequency might not be the worst at all frequencies). The automotive industry generally tests three different orientations. But even with that extra testing (and the additional test time it requires), things can be missed. I’ve seen cases where a unit passed traditional ALSE immunity testing then failed during vehicle level (ISO 11451) immunity. When that unit was re-tested in a reverb chamber, it replicated the failure seen on the vehicle. Given that the goal of module testing is to catch issues early instead of finding them late in the program, much of the automotive industry has been strongly encouraging units to do immunity testing in reverb chambers.
For the automotive industry in particular, reverb testing saves a lot of time (and time in a test chamber = money). It’s well known that radiated immunity can be one of the most time-consuming tests, triply so for ISO 11452 testing, where three separate orientations are required. Reverb testing cuts down that test time by needing only one UUT orientation, roughly a third of what it would take in an ALSE. However, even for aerospace/defense RS103 testing, the time savings are significant: you don’t need to test in two polarizations, and you don’t need multiple antenna locations to cover a large test area at high frequencies.
Of course, nothing is an unqualified good. You generally don’t want to test units with sensitive RF components in a reverb chamber since they’re harder to protect and the field strengths can get very high. You must also consider each chamber’s Lowest Usable Frequency (LUF). Below that frequency, it can’t maintain a volume of field uniformity (see Figure A.5 of IEC 61000-4-21 for a good illustration)). The LUF is largely determined by the physical size of the chamber, where reaching lower frequencies requires a bigger chamber.
If you can access a reverb chamber and do your testing there, IEC 61000-4-21 can be an invaluable resource. It goes through the mathematical details of setting up and calibrating a chamber for either emissions or immunity (or shielding effectiveness) testing. The math can look intimidating and requires a significant amount of statistics, but wading through it should be trivial compared to the cost of longer testing in an ALSE—or missing problems that you must then troubleshoot right before product launch.
