Meaning
Verification processes confirm that the electromagnetic field generated inside an anechoic chamber is homogeneous across a defined area. Field uniformity calibration is the procedure used to measure and document the variations in field strength over a grid of points to ensure they remain within specified limits. This check must be performed before the chamber is used for product testing.
Chamber Validation
Physical arrangement of absorbers and antennas determines the quality of the generated field. During field uniformity calibration, a transmit antenna is placed at one end of the chamber, and a field probe measures the field strength at sixteen points on a vertical plane. This measurement ensures that the field is uniform enough to provide reproducible test results.
Data Computation
Statistical analysis of the measured field points determines the acceptability of the chamber. When analyzing the results of a field uniformity calibration, the data must show that the field strength at a high percentage of the points lies within a six-decibel tolerance window. This calculation is repeated for each test frequency and antenna polarization.
If the field does not meet this requirement, the absorber layout or antenna positioning must be adjusted. This mathematical rigor ensures that the test environment is highly controlled.
Regulatory Compliance
International standards dictate the frequency of these validation procedures. Executing a field uniformity calibration annually ensures that the chamber continues to meet the requirements of standards such as IEC 61000-4-3. This ongoing validation is a prerequisite for maintaining laboratory accreditation.
