Total Field Reconstruction in the Near Field Using Pseudo-Vector $E$-Field Measurements

Exposure assessments in the frequency range above 10 GHz typically require knowledge of the power density very close to the radiator (at 2-mm distance), which can be obtained through the total electric and magnetic fields. However, phase measurements are often not feasible in this frequency range, in particular in the reactive near field. We developed a novel phase reconstruction approach based on plane-to-plane reconstruction algorithms. It uses E-field polarization ellipse information, which can be obtained extremely close to the source with probes based on the pseudo-vector sensor design. The algorithm's robustness and accuracy were analyzed and optimized for distances of a fraction of the wavelength λ, and a comprehensive set of realistic exposure conditions was simulated to evaluate the algorithm. For distances greater than λ/5, the error of the spatially averaged peak incident power density is found to be below 0.5 dB. Measurements in four different antenna prototypes revealed that the simulated deviation of reconstructed averaged power density was consistently below 1.1 dB for distances as close as 2 mm, i.e., smaller than the estimated total experimental assessment uncertainty of 1.4 dB. This demonstrates that the power density can be reliably determined by measurements as close as λ/5 from any transmitter.