Behavior of several antenna topologies near the human head at the 2.4-2.5 GHz band

The increasing growth of wireless devices operating at the 2.4-2.5 GHz band near the human head forces the antenna community to improve the robustness of the radiating system to the undesired effects caused by the proximity of the human head. In this sense, this study is focused on assessing the electromagnetic performance of several antenna topologies in the presence of the human head with the objective of determining the topology that maximizes the ratio between the radiated power in free space and the power absorbed by the human head. With this aim, the main antenna parameters [radiation efficiency, radiation patterns, and specific absorption rate (SAR)] of several antenna topologies (dipole, loop, slot, and microstrip patch) operating at the industrial, scientific, and medical 2.4-2.5 GHz band close to the human head are measured and compared. The experimental results demonstrate that the best performance is achieved by the microstrip patch antenna because it presents less human head absorption and less SAR, thus maximizing the radiated power. The study also states that the effect of the human head proximity over the radiation pattern increases the directivity in all cases under study except the patch case where the effect is negligible. Hence, it is possible to conclude that the microstrip patch is a good candidate for wireless devices operating close to the human head because it not only maximizes the ratio between the radiated power and the power absorbed by the human head but also contributes to reduce SAR.