On Actual Maximum Exposure From 5G Multi-Column Radio Base Station Antennas for Electromagnetic Field Compliance Assessment

The traditional approach of radio frequency electromagnetic field exposure compliance assessment is highly conservative when applied to radio base station antennas implementing dynamic beamforming. In this paper, an analytical model based on the queuing theory with a hyper-exponential service distribution time is developed to assess the time-averaged actual maximum downlink exposure of 5G multi-column radio base station antennas by taking into account the effects of beam scanning over time in free space. Using the measured antenna radiation patterns, the 5G downlink antenna precoding codebook, and assuming a conservative user equipment distribution, the ratio of the actual maximum exposure to the theoretical maximum exposure with 100% traffic load and 75% time-division duplex downlink duty cycle is found to be less than 0.5 and 0.3 for four-transmitter and eight-transmitter radio base station antennas, respectively. These results show that assuming constant peak power transmission in a fixed direction leads to an overestimate of downlink exposure also from conventional antennas characterized by only a few transmitters in addition to massive multi-input multi-output products.