This paper presents a triple-band open-ring high-gain high-efficiency antenna for 2.45/3.0/3.45 GHz wearable applications. The proposed antenna operates at 2.45 GHz for Industrial, Specific, and Medical (ISM) applications, 3.0 GHz for military applications, and 3.45 GHz for Worldwide Interoperability for Microwave Access (WiMAX) applications. The proposed triple-band antenna has excellent features for offbody communication, which has directional radiation pattern, high gain, high efficiency, low-specific absorption rate (SAR), and comfortability for wearers. In order to attain these features, the antenna structure consists of two substrates, a rigid substrate and a textile substrate. Two open-ring radiators and a 1 by 2 power divider feeding network are printed on a low-loss rigid substrate. In addition, a square conductive textile is adhered on the backside of the textile substrate. The open-ring radiator generates triple-band at 2.45, 3.0, and 3.45 GHz, in which the inner open-ring excites two resonant modes at high frequencies of 3.0 and 3.45 GHz. The outer open-ring excites a single resonant mode at a low frequency of 2.45 GHz. The outer annular ring is shorted to the ground plane by a shorting pin to miniaturize the antenna size and additionally maintain antenna stability. The conductive textile works as a full-ground plane or protective shield to reduce the electromagnetic waves toward the human body. Therefore, the SARs are significantly minimized. The compatibility of the proposed antenna for off-body communication is verified by measuring the antenna performance in free-space and on phantom/human bodies. The simulated and measured results show very good agreement.INDEX TERMS off-body, SAR, triple-band, flexible substrate, wearable antenna.

A wearable dual-port button antenna that excites pattern-diversity dual-polarized waves is proposed for on-/off-body applications. Its simple structure comprises of two radiators and a common ground plane designed into two substrates. The crossed-dipole radiator is made by two symmetric bowtie dipoles printed on a circular-shaped semi-rigid substrate, which covers an ultra-wideband (UWB) application with circular polarization and directional radiation patterns, high gain, and high efficiency suitable for off-body communication. The annular-ring radiator and common ground plane are made by a conductive textile on the square-shaped flexible-felt substrate. The annular-ring radiator is shorted to the ground plane using four vias, which generates triple TM modes covering the 2.45/5.85 GHz wireless body area networks (WBAN) with omni-directional radiation patterns and a 3.8 GHz C-band with a directional radiation pattern suitable for on-/off-body communications. The fabricated antenna is verified by measurement in both free space and phantom body environment. Measurements agreed well with simulations. Simulated specific absorption rates (SARs) under US and EU standards are below the safe level, making the proposed antenna suitable for on-/off-body communications.INDEX TERMS button antenna, circular polarization, dual-mode, dual-polarized, wearable antenna. I. INTRODUCTIONWireless body-area networks (WBANs) have drawn significant attention in the internet of things (IoTs), especially in biomedical systems for healthcare, physical training, and patient recovery progress. In such applications, the biological conditions, including body temperature, heart-rate, and blood pressure, are collected in real time by various devices. The acquired data are transferred to an external hub or station. The wearable devices allow doctors or physical trainers to monitor patients and provide spontaneous action as needed. This is known as off-body channel communication, which requires an antenna with acceptable gain and directional radiation pattern. Various types of wearable antennas are proposed for off-body communications [1][2][3][4][5][6][7][8][9][10][11][12][13]. However, all these antennas have linear polarization (LP), which may lead to polarization mismatch caused by the constant movement of the human body. To tackle this issue, circularly polarized antennas that have been used as wearable antennas can be adopted to mitigate polarization mismatch [14][15][16][17][18][19][20][21]. The other communication establishes the internal links between the wearable devices on the body, called on-body channel communication, that requires an antenna with omnidirectional radiation pattern to suppress the radiation in unwanted directions. Various kinds of on-body communication antennas have been presented [22][23][24][25][26][27][28]. Both on-body and off-body communications require the antenna with compact size, high efficiency, low specific absorption rate (SAR), and comfortability to wearers. When nodes on the body communicate each other, ac...

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A compact broadband circularly-polarized wearable antenna is presented for wireless body area network (WBAN) off-body communications. The proposed antenna comprises two substrates, a semirigid substrate with low loss-tangent and a textile substrate, that can boost the antenna performance while maintaining wearer comfort. Initially, a crossed-dipole as a fundamental radiator that radiates a circularly polarized (CP) wave is printed on the semi-rigid substrate. A pair of L-shaped slits are loaded into crosseddipole arm, which significantly miniaturizes the antenna size. A magneto-electric dipole as a parasitic element is loaded to widen axial ratio bandwidth (ARBW) and impedance bandwidth (IBW). A conductive textile is attached to the textile substrate as the ground plane to minimize the specific absorption rate (SAR). The simulated SAR at 5.85 GHz is below the US and EU limit standards. The proposed antenna has solved typical issues in wearable antenna design such as low gain, low radiation efficiency, large size, and narrow IBW and ARBW, while still providing comfortability to wearers.INDEX TERMS crossed-dipole, magneto-electric dipole, SAR, WBAN, wearable antenna.