This letter presents a novel design of a uniplanar compact electromagnetic bandgap (EBG) for millimeter-wave (mm-wave) wearable antennas. The unit cell of the EBG has a flexible fractal design with self-similar window-like structure, which can be easily fabricated at millimeter-scale. The fabricated EBG is a 3$\times$3 cell array laser-cut from adhesive copper foil on polyester fabric substrate. Results show that the gain and °10 dB bandwidth of a wearable coplanar waveguide (CPW) antenna backed by the proposed EBG are improved by 3 dB, and 40%, respectively, across the frequency range from 20 to 40 GHz. Backward radiation is also decreased by 15 dB, significantly reducing the potential health risk posed by the radiating antenna to the human wearer. Furthermore, on-body measurements show that the CPW-EBG antenna performances are not highly sensitive to human body proximity.

With the rapid development of wireless communication technology and the Internet of Things (IoT), wireless body area networks (WBAN) have been thriving. This paper presents a triband patch antenna with multiple slots for conformal and wearable applications. The proposed antenna operates at 5.8, 6.2, and 8.4 GHz. The antenna was designed with a flexible polyethylene terephthalate (PET) substrate, and the corresponding conformal tests and on-body performance were conducted via simulation. The antenna demonstrated promising gain and acceptable fluctuations when applied on curvature surfaces. The specific absorption rate (SAR) for on-body simulation also suggests that this antenna is suitable for wearable applications.

This paper presents a metasurface-based linear-to-circular polarization converter with a flexible structure for conformal and wearable applications. The converter consists of nested S- and C-shaped split ring resonators in the unit cell and can convert linearly polarized incident waves into left-handed circularly polarized ones at 12.4 GHz. Simulation results show that the proposed design has a high polarization conversion rate and efficiency at the operating frequency. Conformal tests are also conducted to evaluate the performance under curvature circumstances. A minor shift in the operating frequency is observed when the converter is applied on a sinusoidal wavy surface.