Meaning
Calibration procedures in radiated power measurements utilize a known reference dipole to determine the exact transmitter output by replacing the device antenna. This technique, known as antenna substitution, removes the variable gains and cable losses of the test environment from the final measurement equation. The process isolates the electromagnetic characteristics of the emitter from the instrumentation setup to establish a high degree of precision in compliance data.
It applies primarily in open area test sites and anechoic chambers where directional characteristics must be verified.
System Calibration
Signal generators feed the substitution antenna at the exact frequency of the device under test to replicate the observed field strength. Engineers use antenna substitution to establish the equivalent isotropic radiated power without relying on theoretical antenna gains. The measurement requires a calibrated dipole or horn antenna whose factors are traceable to national metrology institutes.
Path Calculation
Attenuation losses are resolved by comparing the generator power to the initial device reading. This step bypasses the need for complex mathematical models. It ensures that the calculated power represents the actual performance.
Certification Route
Federal regulatory bodies accept this laboratory routine as the most reliable method for verifying compliance with maximum radiation limits. The substitution method holds greater weight than calculation from direct conduction measurements because it accounts for case radiation and board level coupling. It remains the gold standard for final module approvals.
