Estimation of the average power density in the vicinity of cellular base-station collinear array antennas

This paper investigates the character of the average power density in the c lose proximity of base-station antennas, where human exposure to electromag netic fields radiated from such radio-frequency (RF) sources Is the highest . The concept of average power density is used since, in proximity of a lar ge array antenna, the direction of the power flow at a given point is not r eadily predictable because of the substantially diverging path lengths and direction of propagation of the energy arriving from different array elemen ts, This quantity is shown to have a marked cylindrical decay near the ante nnas, which converts to spherical in the far field, On this basis, a set of simple prediction formulas is derived to allow the estimation of the avera ge power density with good precision. The latest IEEE C95.1-1999 Standard f or RF safety calls for spatially averaged measurements of incident power de nsity to verify compliance to maximum permissible exposure limits. The adva ntage of using the concept of average power density and the resulting predi ction formulas is that the evaluation of the exposure of humans near cellul ar base-station antennas becomes extremely simple during surveys when large computerized scanning equipment may not be available.