Flexible circularly polarized antenna with axial ratio bandwidth enhancement for off-body communications

A flexible circularly polarized (CP) wearable antenna is proposed for a wireless body area network at the 5.8-GHz industrial, scientific, and medical band. The proposed antenna is made of flexible polyimide and foam material. The CP radiation is enabled by loading two pairs of shorting pins on a rectangular patch antenna. The 3-dB axial ratio (AR) bandwidth is doubled by adding two inverted L-shaped parasitic stubs on both sides of the antenna. For validation, the antenna with the dimensions of 0.68 lambda(0) x 0.68 lambda(0) x 0.044 lambda(0) was fabricated and measured in various scenarios with an impedance bandwidth of 6.6% (5.67-6.05 GHz), an AR bandwidth of 3.85% (5.730-5.955 GHz), and a peak gain of 7.2 dBi. The measured radiation in the off-body direction is achieved with a half-power beamwidth of 65 degrees and a 3-dB AR beamwidth of 84 degrees. With the specified input power of 100 mW, the specific absorption rates are 0.613 and 0.294 W/kg in 1-g and 10-g average tissues. Moreover, through analysing the link budget a reliable communication can be guaranteed within 20 m in indoor line-of-sight environments.