Distributed antenna systems for wireless handheld devices robust to hand loading

The performance of handset antennas is strongly affected by the user interaction. In particular, the close proximity of the user's hand when holding the phone usually degrades the behavior of the antenna by introducing detuning effects and efficiency decrements. With the aim of mitigating such negative effects, the present paper proposes a distributed antenna system comprising three monopoles strategically arranged along the ground plane of a wireless handheld device. This configuration not only improves the performance of the radiating system with respect to that attained with a single monopole antenna or a distributed antenna system of two monopoles, but also increases its robustness to the hand loading effect. In order to assess the benefits of the proposed technique, simulated and measured results in free-space as well as regarding the presence of a hand phantom are compared with previous techniques based on a single monopole and a distributed antenna system of two monopoles. The experimental results demonstrate that the proposed distributed antenna system of three monopoles improves the bandwidth (34% for ${\hbox {SWR}} \leq 3$ (693-978 MHz)), the efficiency in free-space, and becomes more robust to the hand loading effects than a single monopole solution and a distributed system of two monopoles.