Assessment of Combined SAR for Low Power Radio Base Stations with Multiple Antennas

In this paper, we investigate when the phase shift between the elements in an array of two dipole antennas can be disregarded for Specific Absorption Rate (SAR) assessments. It is found that at a short assessment distance (one tenth of wavelength from the phantom), the antennas behave like individual electromagnetic sources. Thus, the maximum of combined SAR when both antennas transmitting simultaneously is well-approximated by the maximum SAR of individual antennas. In addition, for antenna separation distances of half a wavelength or larger, the variation of SAR with the phase shift among the antennas is small. Therefore, measuring SAR with antennas operating simultaneously disregarding the phase shift provides an accurate estimate of the exposure leading to a significant reduction in the measurement time. The results obtained for the array of dipole antennas are verified by analyzing a low power Ericsson 5G radio base station product with four antenna branches.