Reconstruction of currents from EMC near-field measurements by means of continuity equation constraints

Electromagnetic compatibility (EMC) is a challenging task in electrical engineering. Near-field scanning provides an insight into the physical behavior of circuits and thus allows understanding the problems. Therefore, near-field scanning enables a well-directed optimization regarding EMC in electronic systems. However, it is a thorough task to gain valuable information from the measured probe signals. One of this valuable information is the distribution of currents in printed circuit boards. In context of EMC, even small current amplitudes are critical. So, the sensitivity of the probe is decisive and due to that there is a lower limit for the probe size. However, the fields across bigger probes are not homogenous and probe compensation is necessary. Additionally, it is advantageous to gain more information by the use of probes with multiple outputs. The usual way to reconstruct the current distribution is a two-step approach with the determination of the electromagnetic fields in an intermediate step. Here, a method for directly mapping dipole sources is analyzed in the context of probes with multiple outputs and simple microstrip devices under test. Parameter studies regarding the number and positions of the dipoles are carried out. Furthermore, the technique requires some a priori information. We propose using a discrete form of the continuity equation as a constraint. By this constraint a significant improvement is achieved.