A magnetic field probe consisting of a LiNbO3 optical waveguide modulator and a loop antenna element was developed to enable accurate measurement of magnetic near-fields in the gigahertz range. The invasiveness of the probe was assessed by using it to measure the magnetic field distribution above a patch antenna operating at 2.49 GHz. The measurements were compared with those obtained using a shielded loop probe. The experimental results obtained using the probe were also compared with simulation results obtained using a finite-difference time-domain (FDTD) method. The overall results indicated that the optical waveguide probe was capable of accurately measuring magnetic near-fields with low disturbance of the measured fields.

Electromagnetic field probes inevitably disturb the original distribution of the field when they are positioned close to a device. This disturbance in turn affects measurement accuracy and device operation. We developed an optical magnetic field probe, comprising a loop antenna element and an electro-optic crystal, for highly accurate magnetic near-field measurement in the GHz frequency range. We analyzed the invasiveness of the optical magnetic field probe quantitatively both experimentally and using finite difference time domain simulation. We found that eliminating the metal cable reduced the disturbance of the surrounding field that was to be measured. In addition, we investigated the magnetic field detection characteristics of the probe and its influence on the operation of a microstrip line. The optical magnetic field probe was less invasive and provided more accurate measurement.