In-phase versus out-of-phase distributed antenna systems for wireless handheld devices

Hand loading usually degrades the performance of handset antennas. With the aim of providing a solution robust to the human presence, this paper discloses a distributed antenna system fed in-phase capable of mitigating undesirable hand loading effects while providing enhanced performance. The solution consists of a passive array of two resonant coplanar monopole antennas inspired in the Hilbert geometry. Input impedances of both monopoles are combined into a single input-output port through two transmission lines featuring equal phases. This combination allows not only improving the performance of the radiating system with respect to that attained by a single monopole antenna, but also providing a symmetric solution immune to the finger location. The solution is compared with a single monopole and a distributed antenna system fed out-of-phase. Simulated and measured results demonstrate that the proposed design is capable of providing operation in the communication standards GSM850/GSM900 as well as in the UHF part of the LTE-Advanced while maintaining the same electromagnetic performance with certain independence of the finger location.