A pattern-reconfigurable antenna design for body area networks communications

This article presents a novel pattern-reconfigurable antenna based on theory of characteristic mode for body area networks (BAN) communication. The radiation pattern of the antenna is able to switch between the omnidirectional pattern and broadside pattern, which can satisfy on-body and off-body communication links simultaneously. An array of 4 x 2 rectangular plates with the off-body communication mode at BAN frequency band is used as the main radiator, and four copper posts between the radiator and the ground are introduced to generate the on-body mode. A simple feeding network is designed to selectively excite the two modes. The footprint of the proposed antenna is 0.43 lambda(0) x 0.43 lambda(0) x 0.05 lambda(0). For demonstration, the proposed antenna has been fabricated and measured both in the free space and on the phantom. The measured results agree well with the simulated ones. Furthermore, the issue of the specific absorption rate (SAR) is studied. The peak SAR values of the proposed antenna in two communication modes are far below the Federal Communication Commission standard. In addition, for practical application, the link budget of the on-body link is investigated. The stable impedance and radiation properties, the low SAR values and the reliable communication ability make the proposed antenna be a suitable candidate for BAN communications.