Assessment of Compliance With RF EMF Exposure Limits: Approximate Methods for Radio Base Station Products Utilizing Array Antennas With Beam-Forming Capabilities

The importance of antenna arrays with beam-forming capability is expected to increase in future mobile communication systems with the ongoing development of new radio access technologies involving higher frequency bands and massive MIMO concepts. In this paper, various approximate methods for radio frequency electromagnetic field compliance assessments of radio base station products utilizing these antenna arrays are investigated with the focus on front compliance distances. For electrically large arrays, the results show that accurate compliance boundary dimensions may be obtained using a field-combining procedure of assessment results for a centrally placed element. For smaller arrays, an overall improvement in accuracy is possible by complementing the center element solution with results for a handful of selected edge and corner elements to better characterize the array behavior. Compared with a general and straightforward approach based on field combining of embedded assessment results for each element, the approximate methods allow for significant reductions of the total assessment time.