Flexible CPW-Fed Antenna for Ultra-wideband Wearable Application

This paper introduces a compact, slotted coplanar waveguide (CPW)-fed antenna that exhibits a wide bandwidth (fractional bandwidth $\gt \mathbf{5 0 \%}$) within the ultra-wideband (UWB) range, and is also flexible. The antenna design features hexagonal rings that are cut and slotted on a polydimethylsiloxane (PDMS) substrate to achieve these characteristics. The slotted hexagonal ring radiator is fed by a tapered CPW, positioned centrally on a trapezium-shaped ground plane. The antenna operates effectively over a frequency range of 1.68 to 9.03 GHz, achieving a total impedance bandwidth of 7.35 GHz ($\mathrm{S} 11\lt -10 \mathrm{~dB}$ for $1.68-9.03 \mathrm{GHz}$, VSWR <2). The peak gain across the band is $\mathbf{6. 7 1} \mathbf{~ d B i}$. Through various design iterations, the peak gain is observed to be 6.71 dBi at 6.5 GHz and 4.07 dBi at 2.4 GHz. Additionally, the antenna maintains an axial ratio $(\mathrm{AR})\lt 3 \mathrm{~dB}$ from 1.75 to 1.83 GHz, and a specific absorption rate (SAR) of $1.33 \mathrm{~W} / \mathrm{kg}$ for 1 g of tissue. The overall dimensions of the antenna are $95 \times 80 \mathrm{~mm}^{2}$.