Whitepaper

An Effective Method of Probe-calibration in Phase Resolved Near-field Scanning for EMI Application

Published by Amber Precision Instruments

This paper presents a time-domain broadband calibration method for E- and H-field probes used in phase-resolved near-field EMI scanning. A comb generator drives a 50Ω microstrip trace, creating known fields (simulated in CST) across 10 MHz–1 GHz in a single waveform capture. The probe factor — a complex, frequency-dependent ratio of field strength to oscilloscope voltage — is determined by referencing measured voltage to simulated fields, capturing the full probe-cable-amplifier chain in one shot. Validated against TEM cell calibration (difference under 1 dBc) and confirmed via scanning of a microstrip-copper patch test device, the method shows under 20% relative error in strong-field regions.