A novel vector near-field scanning system for emission measurements in time-domain

Traditionally, measurements of electromagnetic interference have been performed by EMI receivers operating in the frequency domain. Radiated emission measurements according to CISPR 16-2-3 are carried out below 1 GHz on open area test sites or in anechoic chambers with a conducting floor. Above 1 GHz, the measurements are carried out with a non-reflecting floor. The emission measurements are performed at several heights and angular positions to measure the maximum interference. Typical distances between the device under test and the antenna for measurements are 10 m for the frequency range 30 MHz-1 GHz. Time-domain measurements using the short-term fast Fourier transform have been introduced in the standards CISPR 16-1-1 and CISPR 16-2-3. They allow to reduce the test time significantly. Alternative methods, such as the measurement in a GTEM cell at three positions, have been introduced to reduce the test time. However, a drawback of the test methods for radiated emission measurements is the limited characterization of the device under test regarding near- and far-field in a spherical way. In this paper a novel vector near-field scanning system operating in time-domain is presented. Multichannel time domain EMI measurement systems open up new possibilities such as source reconstruction and far field evaluation. Using methods for stochastic electromagnetic field modeling, we present a near field scanning system that allows for source separation.