Impact of Electromagnetic Properties of Textile Materials on Performance of a Low-Profile Wearable Antenna Backed by a Reflector

Abstract

This paper focuses on the characterization of the electromagnetic (EM) properties of textiles (polar fleece, cotton, denim, polyester, and polyamide-elastane) and study of their impact on the performance of a wearable antenna. EM properties are measured by the cavity perturbation method, and it is found that the textile materials exhibit low values of complex relative permittivity between 1. $2+i0.002$ and 1. $9+i0.1$. A hexagonal-shaped monopole antenna with a substrate from polar fleece and high body-antenna isolation (front-to-back ratio 31 dB) is designed to serve the performance baseline. Additionally, prototypes on cotton, denim, polyester, and polyamide-elastane substrates are simulated, fabricated, and measured. Results show that radiation efficiency, gain and directivity decrease with increasing dielectric losses in the textile substrate. Further numerical investigations reveal that each of these five textile antennas achieves stable on-body performance in the frequency range of 2.4 to 2.5 GHz when it is placed on a flat phantom.