Ground plane booster antenna technology: Human head interaction: Functional and biological analysis

Performance of handset antennas is strongly affected by the user interaction, namely the close proximity of the human head in talking position considerably affects the behavior of a radiating system. However, different radiating systems are not equally affected by the presence of the human head since the effects are highly dependent on the principle of operation associated to each radiating system. This paper is focused on assessing human head effects regarding different radiating systems concerning two aspects: functional (reflection coefficient, efficiency, and radiation patterns) and biological (Specific Absorption Rate (SAR)). Particularly, the paper concentrates on comparing the robustness of a non-resonant ground plane booster based solution with resonant structures commonly used in current handsets. Four prototypes are measured in order to compare their performance: a dual-band PIFA, a hexa-band PIFA with a slotted ground plane, a set of coupled monopoles, and a compact radiating system based on the excitation of the ground plane mode through a set of non-resonant ground plane boosters. A figure of merit relating the antenna efficiency with the SAR values is proposed for comparison purposes. The study demonstrates the robustness of the compact radiating system.