An Analysis of Vector Estimation for Uncertainty Reduction in Evaluating the Specific Absorption Rate of Multiple Transmitting Antenna Devices

Advanced communication systems utilizing multiple transmitting antennas working in a same frequency, such as phased array antennas or MIMO (Multi-Input Multi-Output) antennas, recently receive more and more research attentions. One of technical issues, which certainly need to take into account, is the electromagnetic compatibility. In particular, the evaluation of Specific Absorption Rate (SAR), in the aspect of RF safety specification, is an essential requirement. This paper presents a technique of using vector electric field probes to evaluate the maximum SAR of multiple transmitting antenna devices. Thanks to the information of the phase and magnitude of the measured electric field from the vector probes, the electric fields, or SARs, corresponding to different sets of relative phases of antennas can be estimated from measured E-fields when antennas are turned ON/OFF alternatively. Fundamental concepts are presented, and the errors caused by estimation are analyzed. Index Terms—SAR, estimation, multiple-antenna transmitters, MIMO, vector probes.