Design of Quasi-Endfire Spoof Surface Plasmon Polariton Leaky-Wave Textile Wearable Antennas

Abstract

A new design for a quasi-endfire spoof surface plasmon polariton (SSPP) leaky-wave antenna (LWA) is presented for wearable application. The antenna consists of an ultra-thin corrugated metallic structure screen-printed on a flexible textile substrate, which supports extremely confined spoof surface plasmon polaritons. To enable a highly directional leaky mode, two unit-cell designs with different surface impedances are incorporated to realize binary perturbations on the in-plane wavenumber. An auto-adaptive multi-objective optimizer (MOO) is utilized to intelligently design the surface impedance configuration, which achieves significant dimensional reduction compared to the periodically modified SSPP LWAs. A final miniaturized version with 28-unit-cells achieved about 70% size reduction in comparison to the longer design of 75 unit-cells. For proof of concept, the antenna is designed and optimized for operation at 6 GHz. A bandwidth of >200 MHz (5.90 GHz - 6.13 GHz) is achieved, centered around 6 GHz, for which the highly directional endfire pattern can be tilted to 22° and 14° for the 28 and 75 unit-call designs, respectively. The measured results agree well with the simulations. Meanwhile, experimental results show that the Specific Absorption Rate (SAR) is lower than 1.6 W/kg standard when the antenna is 2 mm away from the human phantom. This textile-based antenna realized with advanced screen-printing technology is extremely suitable for garment integration due to its high flexibility, low-profile, good fabrication accuracy, and robustness in its performance.