Speaker
Description
In high-frequency bands such as 28 GHz used in 5G communication systems, base stations are installed closer to users, along with the adoption of beamforming technology. As a result, the human body is exposed to non-uniform electromagnetic fields generated by multiple beams. The ICNIRP guidelines on electromagnetic field exposure limits were revised in 2020, expanding the application range of whole-body averaged specific absorption rate (WBA-SAR) limits from 10 GHz to 300 GHz. Since WBA-SAR is difficult to measure directly, it is important to clarify its correlation with measurable physical quantities through simulation. However, simulations at high frequencies, such as 28 GHz, require enormous computational resources. Therefore, we are investigating a method to efficiently evaluate exposure from beamforming antennas by calculating exposure levels through the superposition of pre-calculated data for various beams. In this study, we propose a method to represent multiple beams as a combination of fewer beams. Using this method, we evaluate the variation in exposure levels according to the beam direction and distance for beams formed by an 8 × 8 element array antenna. The worst-case WBA-SAR values were compared with broadside beam exposure values at each distance. Broadside beam exposure at the height of the chest was lower than worst-case values by 0-10 % for vertical polarization and 2-12% for horizontal polarization across 1 m to 4 m separation distances.
