Methods and Practices for In Situ Measurements of RF EMF Exposure From 5G Millimeter Wave Base Stations

In this article, a methodology for in situ measurements of the radio frequency electromagnetic fields exposure from 5G base stations (BSs) operating at millimeter wave (mmW) frequencies is presented. Measurements were performed in proximity of two BSs operating around 28 and 39 GHz. The measured power density from the BSs when extrapolated for the maximum transmit power was below 30 mW/m ² at a distance of about 10 m (i.e., below 1% of the ICNIRP limits). A systematic analysis of the challenges related to in situ measurements of 5G mmW exposure is conducted for the first time. It was found that exposure measurement procedures developed for frequencies below 6 GHz (such as those based on extrapolation of the synchronization signal block) are generally applicable also at mmW. When in line-of-sight, dual-polarized directional antennas can be used to accurately characterize the maximum exposure. The angular variation of the incident power density at the measurement location was studied by means of a motor-controlled panorama tilt unit. At the same time, a network counter was used to monitor the directional time-averaged power transmitted by the BS. The study is of importance to standardization committees addressing measurement techniques to assess exposure from mobile networks.