Performance Analysis of Incident Power Density Evaluation by Inverse Source Method for Compliance Assessment at Quasi-Millimeter and Millimeter Wave Bands

In modern communication systems including the fifth-generation mobile communication system (5G), quasi-millimeter, and millimeter wave frequencies above 6 GHz are utilized. At these frequencies, the incident power density is employed as a metric to assess the compliance of wireless devices to human exposure limits in international guidelines and national regulations. In this article, the performance of the inverse source method (ISM) for incident power density evaluation is investigated in terms of accuracy and operational costs, i.e., measurement and computational costs. The ISM is based on the surface equivalence theorem, and it reconstructs the incident power density close to the device under test from a field measured in a more distant region. The comparison of the performance between the ISM and the conventional plane-wave spectrum method by computational simulation shows that the ISM has an advantage over the conventional method in robustness to the truncation of the measurement region. The ISM reduces the number of measurement points to a quarter for the reconstruction of the spatially averaged incident power density in an error less than 0.4 dB. These findings in the computational simulations are also validated by the measurements of a standard horn antenna and array antennas operated at 28 GHz.