A Fast and Rigorous Assessment of the Specific Absorption Rate (SAR) for MIMO Cellular Equipment Based on Vector Near-Field Measurements

Abstract

This paper introduces a rigorous and fast procedure for accurate assessment of the peak averaged specific absorption rate (SAR), quantifying the user exposure to the electromagnetic field radiation from new-radio communication devices. Focus is lent to the specific class of user equipment that exploit multiple-input multiple-output (MIMO) technology and using exclusive simultaneous excitations of the active antenna-array system, such as expected on 5G devices. In contrast with the required N(N-1)+1 measurements on traditional SAR systems that only take measurements of the amplitude of the electric field, it is demonstrated in this paper that only N+1 number of measurements are required to evaluate the true SAR of a Nantenna MIMO thanks to using a vector near-field based SAR measurement system.

On the measurement procedures for the assessment of the specific absorption rate (SAR) from MIMO cellular-equipment of fast varying relative phases

“…b. Using N + 1 measurements, follow the method presented in [9,10] in order to obtain, at each point (x, y, z) of the measurement domain, the individual local SAR distributions SAR i (x, y, z) corresponding to an independent excitation of each antenna of the MIMO system.…”

“…As the first step of the measurement method was previously validated in [9,10], the local SAR values SAR 1 (x, y, z) and SAR 2 (x, y, z) corresponding to the two antennas can be assumed to be known in every point of the measurement domain. The corresponding local SAR variations are represented in Figure 5.…”

“…This is for instance the case for antenna array systems where the phase shift is used to control the radiation pattern and the radiation direction. For these systems, the methods presented in [9,10] allow for a rigorous SAR assessment of all the possible configurations of the MIMO system using only N + 1 measurements (where N is the number of antennas of the MIMO system). These fast and rigorous methods, requiring such minimal number of measurements, are made possible through the simultaneous measurement of the amplitude and the phase of the electric field phasor, combined with a vector spectral analysis of the radiofrequency signals for SAR assessment.…”

“…In this paper, a SAR measurement method for MIMO systems with a fast relative phase variation rate is presented. This method is based on the work presented in [9,10] and on the convergence of the time averaged electric field. The proposed method is intended for SAR measurement systems with vector probes measuring the electric field phasor, with a frequential selectivity and a time-domain acquisition of the demodulated radiofrequency signals.…”

“…In this paper, a method for the evaluation of the time averaged SAR is presented. The proposed method is the extension of the work presented in [9,10] to the case of MIMO systems with fast time domain variations. The proposed method is based on the use of vector measurement systems with a finite measurement probes grid and using E-field reconstruction in the measurement volume.…”