Space-Time-Frequency Characterization in Electromagnetic Near-Field Scanning: A Data-Driven Approach

Near-field scanning has become a widely-used tool for diagnosing electromagnetic compatibility and electromagnetic interference issues. However, the transient signal of the device under test often contains multiple frequency bands and exhibits nonstationarity, which poses a challenge for near-field scanning analysis. To address this issue, this article presents a method for analyzing time-resolved near-field radiation based on multiresolution dynamic mode decomposition (MRDMD). The MRDMD approach recursively and hierarchically applies the traditional dynamic mode decomposition (DMD) method. The distribution of DMD eigenvalues determines the slow and fast modes in each level's decomposition, where the slow modes are preserved and the fast modes are used to generate input data for the next level. This yields a multiresolution time-frequency representation of the near-field radiation field, and corresponding spatial distributions for each frequency component are extracted. Two numerical examples involving a single dipole antenna with on-off keying modulation and the activation/deactivation of three dipole antennas are conducted to validate the proposed MRDMD method. The multiresolution time-frequency representation of the near-field radiation shows good agreement with actual results in terms of excitation duration and frequency components. Simultaneously, each frequency component's spatial distributions in the scanning plane are also derived. Thus, our work provides a multiresolution analysis tool for near-field scanning, particularly in cases where space-time-frequency correlated information is required.