Prototype Antenna Array for Near-Field Surface Scanning of Magnetic Field

Near-field magnetic field strength measurements that use scanning antenna arrays require different probe orientations in the array, which can degrade the scanning resolution. The use of omnidirectional probes overcomes this problem, but their application in an antenna array needs to be investigated. In this paper, we developed a prototype antenna array for measuring the amplitude of the near-field magnetic field of the target. To calibrate each probe in the antenna array, we obtained in a simple expression for determining the calibration coefficient of a probe in a TEM cell. We also fabricated prototypes of magnetic probes to measure the amplitude of the magnetic field strength and measured their antenna factor (AF). To validate the magnetic probe prototypes, we measured the magnetic field strength amplitudes generated by an asymmetric transmission line in the frequency range 0.1-5.0 GHz as the probe moved along the scanning plane. We then developed a prototype scanning antenna array and measured the amplitudes of the magnetic field strength generated by an asymmetric transmission line at frequencies of 0.1, 2.5, and 5.0 GHz using this prototype. The antenna array measurement results agreed well with those obtained for a single magnetic probe moving along the scanning plane. This means that the developed prototype antenna array with omnidirectional probes can be used for near-field magnetic field strength measurements.