Methodology for Electromagnetic Field Exposure Assessment of 5G Massive MIMO Antennas Accounting for Spatial Variability of Radiated Power

The technology of massive Multiple Input Multiple Output (maMIMO) antennas introduces new challenges in the Radio Frequency Electromagnetic Fields (RF EMF) exposure assessment of 5G base stations due to the aleatory changes of the radiation direction. The beamforming capabilities of the antenna modify the radiation pattern both in space and in time domain in order to adapt the electromagnetic footprint to the changes of user positions, mobility, and service requests. Recently, Base Station (BS) power monitoring counters per Angular Regions (AR) were introduced in maMIMO antenna technology for monitoring the power associated to specific angular directions. By analyzing the time averaged power reported by ARs power monitoring counters the paper proposes, making use of simulations, a methodology to quantify a statistical spatial power reduction factor (0.05 to 0.5, on the base of the assumptions adopted in this paper) to be applied in the RF EMF exposure assessment process accounting for the variability of the maMIMO antenna radiation pattern. The proposed approach enhances and completes the methodology already described in normative documents for characterizing time variations of the total radiated power. The paper is completed with a sensitivity analysis for the size of each AR with respect to the antenna beam size; the analysis shows that a good spatial resolution is achieved when the AR Region has almost the same size as the beam’s half power beam width.