A method for determination of RF exposure compliance for pico cell base stations by SAR measurements in a flat phantom

With the increasing number of cellular base stations in both indoor and outdoor environments, there is a growing need for simple and accurate methods for RF exposure assessments and for the determination of exposure limit compliance distances for such equipment. For low output power devices, whose compliance distances can be assumed to be short, measurements of SAR in a phantom representing the human body can be feasible. Assessment of SAR by measurements requires technically advanced equipment and stable setups and procedures in order to reduce the uncertainty of the result. With the usage of a box-shaped phantom, the position of the antenna in front of the phantom is easily determined. The shape of such a flat phantom roughly resembles the trunk of a person and can be assumed to be more conservative (i.e. giving higher SAR) than an anatomically shaped homogeneous phantom due to the greater coupling with the antenna. The purpose of this study was to investigate whether flat phantom measurements can be used to accurately estimate the maximum averaged local SAR in a human body exposed to RF fields from small pico base station antennas and if such a measurement method can be used to determine RF exposure compliance distances. The validity of the method was verified by comparing measurements of SAR in a flat phantom with numerical calculations of SAR in an anatomically realistic human model.