Abstract
A new flexible circularly polarized (CP) wearable antenna is proposed for Wireless Body-Area Network systems (WBAN) operating at 5.8 GHz. The circular polarization is enabled by combining a microstrip-line monopole feed and an inverted L-shaped conformal metal strip extended from a coplanar waveguide. The proposed antenna shows satisfactory performance in terms of gain and specific absorption rate (SAR) at a separation of 12 mm from a human body model. To minimize body-antenna separation, a flexible <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$2 \times 2$ </tex-math></inline-formula> artificial magnetic conductor (AMC) was used as a reflector to achieve good performances in terms of gain and SAR. The total footprint of the proposed antenna is only <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$34.4\times34.4$ </tex-math></inline-formula> mm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$0.384 \lambda _{0}^{2}$ </tex-math></inline-formula> ) board of semi-flexible Rogers RT-Duroid 5880 substrate. The final design provides a peak gain of 7.6 dBi and an efficiency of 94.7% when worn on the body. Furthermore, evaluation results indicate that the maximum SAR level decreased by up to 20.42% in comparison with the CP antenna without the AMC. Full-wave EM simulation and experimental results are performed, both in free space and proximity to the human body under different bending scenarios. Overall, the proposed antenna performance has been shown to be robust to structural deformation along the x-axis in comparison to previously reported designs. These features demonstrate that the proposed antenna is a strong candidate for off-body wearable applications.
Highlights
The interest in wireless body area networks (WBANs) has been rising significantly in the development of flexible and wearable devices [1]
The antenna design is based on a simple topology structure to generate a wide-band broadside circularly polarized (CP) radiation
The antenna with and without the artificial magnetic conductor (AMC) reflector enables good impedance matching in free space
Summary
The interest in wireless body area networks (WBANs) has been rising significantly in the development of flexible and wearable devices [1]. Significant frequency shifts occur due to structural deformation resulted in an increase of beam width with a decrease in the gain These antennas have characteristics in common that limit performance, such as low efficiency, narrow bandwidth, frequency shifts, and poor front-to-back ratio (FBR) under different bending conditions, and their complex excitation mechanism made the design uncomfortable to the user. A flexible CP wearable antenna backed by an AMC array structure is designed and investigated for WBAN applications. An inverted L-shape parasitic strip from one side of the coplanar ground planes has been designed to achieve the CP capability at 5.8 GHz. the monopole antenna is backed by a compact 2×2 AMC array, to reduce the backward electromagnetic radiation towards the human body.
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