Interference Mechanisms of Undesired Fields on Shielded Tangential Magnetic Field Probes during Measurement

Shielded tangential magnetic field probes suffer from significant measurement errors due to concurrent coupling of tangential electric field (E_y-field) and vertical magnetic field (H_z -field) during near-field scanning. Existing research lacks a comprehensive analysis of this hybrid coupling mechanism and effective separation methodologies. This study presents the systematic investigation of the hybrid coupling mechanism of E_y-field and H_z-field in shielded tangential magnetic field probes. By establishing equivalent circuit models, the physical paths of capacitive coupling and magnetic flux penetration are clarified, explaining the frequency-dependent behavior of E_y-field coupling transitioning from 20 dB/dec at low frequencies to 40 dB/dec at higher frequencies, and the consistent 20-dB/dec increase of H_z-field coupling. The field separation method is used to achieve effective separation of E_y-field and H_z-field coupling responses in a wide frequency band of 0.01-40 GHz. The inherent crossover frequency (f_k) of the probe is identified as a characteristic parameter, with physical interpretation of its role as a critical point determining the dominant coupling mechanism: H_z-field coupling dominates below f_k, while E_y-field coupling dominates above it. The method is validated through full-wave simulations and measurements on shorted microstrip lines. This work provides a new approach for quantifying undesired field coupling in near-field measurement.