Efficient Experimental Assessment of The Specific Absorption Rate (SAR) Induced by MIMO Wireless Communication Devices; Application of Vector Near-Field Measurement System

Abstract

This paper introduces an efficient procedure for the evaluation of the true exposure level, quantified by the peak averaged specific absorption rate (SAR), of multiple-input multiple-output (MIMO) communication devices operating transmission diversity. As compared to the traditional conservative evaluation of the SAR, that results from the unpractical testing of all the antenna-array states of the device, the assessment of the true exposure level enables higher margin for minimizing the SAR while maximizing the radiation performance of the device.

EMPIR European project for validation of vector array SAR measurement systems

“…Although reference sources have been provided to emulate real devices under test, there are currently no measurements available to compare the similarity of the field strength of a test object with the reference sources. Finally, a new effective procedure for assessing the actual exposure level, quantified by the SAR level, has been developed for MIMO devices used for beamforming [5]. This procedure provides greater flexibility to minimize the radiation and performance of these MIMO devices, compared to the traditional conservative assessment of SAR that results from the impractical testing of all antenna array states of the device with systems that do not use phase information and are less applicable to beamforming systems such as MIMO antennas.…”

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

“…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 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.…”

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

“…A simple and efficient procedure is introduced in [12] for the MIMO SAR evaluation that incorporates a calibration method of the phase reference of the aforementioned independent N field phasor measurements. It is introduced for the specific case of a MIMO system in which it is possible to individually excite the antenna array elements.…”