A wearable dual-band folded-ring antenna, that has directional radiation pattern and offers high-gain, high-efficiency, and low-specific absorption rate (SAR) performance, is presented for 2.45/3.45 GHz off-body communication. The proposed antenna is comprised of two substrates; a folded-ring antenna as a main radiator is printed on a low-loss rigid substrate and a conductive textile is attached to a felt substrate. The conductive textile is used as the ground plane and as a protective shield to prevent incidental electromagnetic waves from propagating toward the human body. The felt substrate provides a comfortable surface for wearers. The antenna performance is verified and shows very good agreement both in free space and on phantom body environment. The measured bandwidths of S11on human body are 5.76% and 4.7% at each frequency band. The maximum broadside gains within the operating bandwidth are 5.1 and 8.6 dB, respectively. The measured radiation efficiencies on human phantom are 91% and 94%, respectively. The SAR values at lower mode based on US and EUR standards under 1 g average and 10 g average are 0.2 and 0.1 W/kg, respectively. At higher mode, the SAR values are 0.1 and 0.04 W/kg, respectively.
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Le et al. (2021) studied this question.