A Wideband Circularly Polarized Antenna With Metasurface Plane for Biomedical Telemetry

This letter presents a metasurface (MS)-based wideband wearable circularly polarized (CP) antenna to communicate with in-body devices. The antenna consists of a crossed dipole, an MS plane and a CP feeding network. The feed network generates a quasi-90° phase delay between each adjacent arm of the crossed dipole. This produces CP radiation and reduces polarization mismatch between the telemetry antenna and the implantable antenna. The MS, consisting of a 5 × 5 unit cell array, functions as a reflector for the crossed dipole to improve forward radiation while maintaining a low-profile structure. This is by designing the unit cells with a near-zero phase reflection over the operating band. To enable conformity with on-body usage, the antenna is designed fully using flexible materials. Textile conductive elements are embedded into a PDMS substrate. It is sized at 106 × 106 × 5 mm3 (1.24λ × 1.24λ × 0.05λ at 3.5 GHz). Results indicated a -10 dB impedance bandwidth from from 2.25 to 6 GHz (90%). The 3 dB axial ratio bandwidth is from 2.9 to 4.95 GHz (52%), with a maximum on-body gain of -10.5 dBi. Finally, the specific absorption rate (SAR) assessment of the antenna indicated values far lower than the limits of the FCC.