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

Nowadays the majority of electrical devices are complex systems with different operation modes and switching elements. The amount of evaluation procedures that are needed to be done for these devices increases drastically. It is pushing standard radiated EMI measurements to the edge, where the advantage between time and the accuracy of measurements should be chosen. Standard low-frequency measurements as CISPR 36, used to evaluate radiated EMI for frequencies below 30 MHz, became too time-consuming and expensive. Proposed improvements which include time-domain multichannel measurements in combination with a three-axis shielded loop antenna can be more time-efficient. Compared to a conventional single-loop antenna, one of the potential challenges is the coupling between loops for the two- and three-axis antenna. This paper investigates the effect of coupling between the individual loops when illuminated with a complex field, which is shown to be the worst-case scenario. Only some minor coupling is observed implying that such a three-axis loop antenna can be used without sacrificing much accuracy, while still providing a significant improvement in the measurement time-efficiency.