Design and Characterization of a Multi-Processed Differential Magnetic Field Probe by Using Asymmetric Calibration Method

In order to improve the spatial resolution of a magnetic near field probe, the design method combining multiple ports with multiple production processes has been proven effective. However, the asymmetry of transmission structure introduced by the junction between two different processes is a key problem that limits the performance of these probes. In this paper, a differential magnetic near field probe (diff-H-probe) combining flexible printed circuit (FPC) process with print circuit board (PCB) process has been manufactured to achieve high spatial resolution. The measurement results show that this probe can recognize a serpentine line with 100~\mu \text{m} -width of trace and 100~\mu \text{m} -space between traces. Meanwhile, an asymmetric calibration method (ACM) has been applied to significantly improve the performance of the diff-H-probe. Some key parameters of the probe with and without using the ACM are compared by using an air-dielectric microstrip line. The compared results show that the detection frequency range of the proposed probe is broaden to 12 GHz. Moreover, the results also demonstrate that the ACM can improve the differential electric field suppression up to 4.1 dB and improve the common mode electric field suppression to 20 dB at the frequency below 12 GHz.