Design of broadband circularly polarized wearable metasurface antenna using characteristic mode analysis

This paper presents a novel broadband circularly polarized antenna for wearable devices. The antenna consists of a microstrip patch and a 3 × 3 metasurface. First, a pair of orthogonal modes of the metasurface is accurately identified using characteristic mode analysis (CMA). Then, the microstrip patch and the improved metasurface structure are used to achieve orthogonal phases, allowing for effective circular polarization. The overall dimensions of the antenna are 38 × 38 × 4.8 mm3. Furthermore, the synergistic working principle of the metasurface and the patch is also analyzed. The measured results show that the −10 dB impedance bandwidth is 62.8% (4.35–8.33 GHz), the 3 dB axial ratio bandwidth is 28.3% (4.85–6.45 GHz), and the peak gain reaches up to 8 dBi. By evaluating the Specific Absorption Rate (SAR), the results comply with the IEEE C95.1–2005 standard, ensuring the safety of wearable antenna. The designed antenna exhibits excellent impedance and axial ratio bandwidth; and has a small size and good gain performance. This antenna can be used for wearable wireless communication devices in the 5 GHz (5.15–5.825 GHz) wireless body area network (WBAN) band.