Efficient Time-Domain Multi-Channel Measurements using a Multi-Axis Antenna for Frequency Range below 30 MHz

Abstract

Radiated electromagnetic interference measurements were traditionally done in the frequency domain. A super-heterodyne EMI test receiver is then analyzing each frequency individually during a sweep across the spectrum. Despite the high accuracy, the time needed for the measurements sometimes reaches several days due to the small bandwidth and thus long dwell time, especially in the lowfrequency range below 30 MHz. Modern time-domain EMI analyzers already created major reductions in measurement time. Some standards require measuring with several magnetic loop antenna orientations with respect to the equipment under test. Instead of the expensive single-channel time-domain analyzers, cost-efficient multichannel digitizers are proposed to perform measurements using several magnetic loop antenna positions and polarizations simultaneously.

Estimation of the Highest Influence on the Measured Results of a Three-axis Shielded Loop Antenna Using Three Transmitting Antenna and Tilted Antenna Methods

“…According to the measurement results which were shown in [6], [10] the highest emission level around an EUT could be measured from the same antenna position in two planes simultaneously. Because of that, the possibility to measure a high level of magnetic emissions in Z plane exist as well.…”

“…changing velocity, or different states like cruising or parking. In [6] the possibility to use multichannel digitizers to read the measurement data simultaneously from multiple sources was discussed and shown. With this opportunity several antennas could be used simultaneously and greatly speed up the measurements.…”

Evaluation of Three-Axis Magnetic Loop Antenna Cross Coupling for Low-Frequency Measurements

“…Several possibilities to reduce the measurement time were studied [6]. Multi-channel time-domain measurements already provide considerable time reduction [7]. As an alternative of one single shielded loop antenna, the multi-axis antenna, made of three orthogonal loops, has been used by amateur radio for several decades [8].…”

“…Van Veen introduced a loop antenna for EM emission measurements, which includes three orthogonal loops, for evaluation of small EUT [9]. The possibility to use three orthogonal loop 60 cm antennas has been investigated in [7], [10]. The combination of multi-axis antenna and multichannel measurement device could provide the evaluation of EM field in three orientations simultaneously.…”

“…However, this is only possible if the radiated EM field is co-polarized with one antenna and un-polarized with another. This is typical for antenna factor measurements using another antenna as a reference source [11], [7]. In this case, the antenna which is measuring a lower value of the EM field will have a less influence on the other one.…”