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 λ 0 × 0.68 λ 0 × 0.044 λ 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° and a 3‐dB AR beamwidth of 84°. 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.