A study on magnetic near-field measurements above a patch antenna using an optical waveguide probe with a loop element

We developed a magnetic field probe consisting of a LiNbO₃ optical waveguide modulator and a loop antenna element for accurate magnetic near-field measurements in the gigahertz range. We confirmed the probe invasiveness by measuring magnetic field distributions above a patch antenna operating at 2.49 GHz using the probe. Then we compared those measured results with those for shielded loop probes. Furthermore, we compared experimental results with finite-difference time-domain (FDTD) method simulation results. Comprehensive results indicate that the optical waveguide probe is suitable for accurate magnetic near-field measurements with low disturbance of measured fields. In addition, phase distribution measurements were done using the probe and a vector network analyzer (VNA). Thereby, we confirmed that the probe is useful for time domain measurements.