Design of a compact multistubs resonator based dual-band flexible wearable antenna with low SAR for sub-6 GHz ISM applications

In this paper, a small size multistubs resonator based flexible wearable antenna is demonstrated for dual-band operation. The proposed antenna is composed of vertically aligned multistubs resonator, a 50 Ω microstrip feed and a defected ground structure (DGS). This configuration of antenna resonates at 2.4 and 5.8 GHz Industrial, Scientific, and Medical (ISM) sub-6 GHz bands. It has a small footprint of 32 × 17 × 0.508 mm³ (0.256 λ_L × 0.136 λ_L × 0.004 λ_L at f_L = 2.4 GHz), with measured reflection coefficient magnitudes (|S₁₁|) of - 15.81 dB with bandwidth of 280 MHz (2.3-2.58 GHz) and - 33.06 dB with bandwidth of 580 MHz (5.42-6 GHz) at 2.425 and 5.72 GHz, respectively. Moreover, it has bidirectional and omnidirectional radiation features due to DGS with a measured peak gains of 1.317 dBi (2.425 GHz) and 4.759 dBi (5.72 GHz). This study also explored a widespread investigation on a parametric study, specific absorption rate (SAR), diverse bending conditions and its interaction with diverse on-body circumstances (by placement on the chest, hand, and leg). The SAR values are 1.29 W/kg (1 g) and 0.88 W/kg (10 g) at 2.43 GHz whereas at 5.8 GHz, the SAR values are 0.507 W/kg (1 g) and 0.257 W/kg (10 g), which well within SAR safe limits. The antenna adhere the effective robustness, stable performance during bending deformations and on-body scenarios which validated the antenna effectiveness for wearable sub-6 GHz ISM band applications.