engleski

Analysis of GSM Base Station Antenna Near Conductive Object : Estimating EM Field Levels in the Near Field

When estimating the potential radiation hazard of a base station antenna system, one often relies on the antenna far-field radiation pattern, while the estimation often refers to the antenna near-field zone. It is widely accepted that this leads to overestimation of the field amplitudes. This work analyzes the typical sector antenna, widely used in GSM system. Antenna near field distribution is calculated using NEC2, for various configurations of antenna installations. Analysis of the antenna in free space shows that the overestimation only happens in the mainlobe, while in all other directions even underestimation can happen. Furthermore, conductive objects in close proximity of the antenna, like in widely-used multiple-antenna configurations, can significantly distort the radiation pattern in a generally unknown manner, leading to unexpected higher amplitudes in the unknown directions. For truly conservative, worst-case EM field estimation, this should be taken into account. The paper concludes with some guidelines on using the modified radiation pattern for such estimation.

base station antenna; near field; EM field estimation

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