Meaning
IEC 61000-4-21 defines the electromagnetic compatibility procedure for testing equipment inside reverberation chambers. The standard specifies methods for generating uniform statistical fields using mechanically tuned stirrers to evaluate radiated immunity and emissions. Compliance testing stops at the boundary of the test facility itself, where chamber calibration verifies field statistics before the device under test enters the working volume.
Chamber Calibration
The validation protocol measures electric field uniformity across the designated working volume before any active assembly undergoes exposure. Technicians rotate paddle stirrers through discrete angular steps while recording vector field components with broadband isotropic probes. Spatial standard deviation calculations across these samples must fall below specified thresholds to confirm adequate modal density for reliable stress application.
Loading Effect
Placing a finished product inside the cavity alters the quality factor of the resonant enclosure through absorption and scattering. The standard requires monitoring this shift because excessive loading compresses the dynamic range of the stirred environment and reduces peak field amplitudes. Engineers quantify the resulting degradation by measuring decay time constants before and after introducing the assembly.
Uncertainty Budget
Measurement confidence depends directly on the number of independent stirrer positions and frequency tuning steps executed during the sweep. The evaluation accounts for cable losses, probe calibration drift, and spatial field variations as combined error sources rather than single margins. Final compliance documentation records these combined variances to prove the radio frequency stress met required severity levels at every frequency band.
