A Wideband and High Sensitivity Probe Design for Near-Field Scanning

In this paper, a wideband and high sensitivity magnetic probe is designed for the near-field scanning. To achieve the high sensitivity, the size of the probe aperture is fixed as 1 mm by 1 mm. On the basis of the fixed size, reducing the length of the loop wire and optimizing the width of the loop wire are adopted to reduce the parasitic inductance and capacitance, in order to increase the highest working frequency of the probe. The working frequency of the probe is up to 20 GHz. At the same time, ground planes, metal on sides and shielding vias are used to suppress the unwanted electric field coupling. The tapered trace, shorting via arrays and coax-thru-hole vias are used to improve the performance of the probe further. The probe is fabricated on a four-layered printed circuit board (PCB) with Rogers substrate and calibrated by a standard microstrip line. Finally, a near-field scanning system with the fabricated probe is set up to measure the magnetic field above a Z-type line. From the near-field scanning results, it can be concluded that the probe can measure the magnetic field accurately.