Continuous Electromagnetic Emission Measurement Setup with Antenna Position Tracking

For measuring the maximum electromagnetic emissions around equipment many test methods use the frequency domain, traditionally using a super-heterodyne test receiver. However, for large equipment under test the frequency domain method is very time consuming when the measurements are performed at low frequencies, below 150 kHz, where small bandwidth and thus long measurement time is needed. Time-domain measurements are now replacing the traditional super-heterodyne receivers, but the commercial time-domain receivers still use a first mixer stage. However, at low frequencies, low cost digitisers can do the same job directly in the baseband. Using fast signal processing, this method allows to continuously measure the radiated magnetic field around the equipment under test. Combined with position tracking, this allows to identify areas of maximum emissions very fast. These positions are then used to obtain a more detailed spectral analysis of emissions by increasing the measurement time over those spots. In result, the whole measurement procedure can be significantly optimized by spending less time over areas of lower interest, and putting more focus on areas of potentially high emission levels. This paper presents the concept as well as an experimental comparison of three antenna movement approaches satisfying the NRE01 and RE101 radiated emissions measurement procedures.