0018-926X (c) 2019 IEEE. Personal use is permitted, but republication/redistribution requires IEEE permission. See http://www.ieee.org/publications_standards/publications/rights/index.html for more information. This article has been accepted for publication in a future issue of this journal, but has not been fully edited. Content may change prior to final publication. Citation information: DOI 10.1109/TAP.2019.2951517, IEEE Transactions on Antennas and Propagation > REPLACE THIS LINE WITH YOUR PAPER IDENTIFICATION NUMBER (DOUBLE-CLICK HERE TO EDIT) < 1 Abstract— In this paper, a novel dual-polarized embroidered textile antenna array with an omnidirectional radiation pattern is proposed for both on- and off-body wearable applications. The flexible antenna is composed of a group of circularly oriented dual-polarized patch antennas excited with uniform amplitude and phase. The antenna array can be wrapped around a cylinder, such as an arm or a leg, for realizing a quasi-omnidirectional radiation pattern in the azimuthal plane, which is highly desirable in both on-body and off-body wearable applications. The operating principles and design consideration for how to achieve the omni-directional radiation and how to avoid radiation nulls are investigated in detail. Moreover, these analytical studies are verified through experimental results. In addition, a dual orthogonal polarization capability is employed to improve the link reliability. Due to the high front-to-back ratio (FBR) exhibited by each patch antenna element, the proposed omni-directional antenna array also features a low Specific Absorption Rate (SAR) and high efficiency, which are extremely important for wearable applications. As a proof-of-concept, an antenna array prototype operating at 5.8 GHz is designed, fabricated, and tested. Measured results agree reasonably well with the simulations in terms of S-parameters, polarization isolation, and radiation patterns, demonstrating that the proposed antenna array is ideally suited for potential wearable applications. Index Terms— Antennas, dual-polarized, embroidery, textile antenna, omni-directional, wearable application. I. INTRODUCTION ODY-centric wireless communication systems are playing an increasingly important role in healthcare, military, and fire-fighting applications [1]-[2]. To facilitate such on-body wireless systems, the antennas are typically required to be flexible, high efficient, and low absorption by human tissue. Moreover, maintaining a reliable link is very desirable for a This work was supported by the National Science Foundation ASSIST Nanosystems ERC under Award EEC-1160483. (Corresponding author: Chunxu Mao). C. Mao, Y. Wu, and D. H. Werner are with the Electrical Engineering Department, The Pennsylvania State University, University Park, PA 16802 USA. C. Mao is also with Institute for Communication Systems (ICS), 5G Innovation Centre (5GIC), University of Surrey, Guildford, GU2 7XH, UK (e-mail: cxm2088@psu.edu, c.mao@surrey.ac.uk). D. Vital, S. Bhardwaj are with the Department of Electrical & Computer Engineering, The Florida International University, Miami, FL 33174 USA. body-centric system since deformation and body movement are likely happened which will degrade antenna performance in a real-time operation. Taking all these issues together, the design of wearable antennas is an extremely challenging task, which is quite different from those of conventional antennas. According to their intended applications, wearable antennas can be divided into two groups, namely on-body and off-body wearable antennas. Over the past two decades, significant attention has been paid to wearable antennas for off-body communications (broadside radiation) based on a variety of different fabrication techniques, such as polydimethylsiloxane (PDMS) [3]-[4], liquid metal [5]-[6], and embroidered textiles [7]-[22]. Owing to its low-loss, low-cost, and easy integrating into garments, embroidered antennas based on flexible textiles are usually considered a better choice for wearable applications. Textile patch antennas were proposed by using probe-fed [7] and aperture coupled methods [8], which, however, are not suitable for implementation in body-worn applications. A textile-based substrate integrated waveguide (SIW) technique was also employed to design wearable antennas for reducing the backward radiation into the body [9]-[11]. It has been demonstrated that the front-to-back ratio (FBR) can also be improved by placing an additional electromagnetic band-gap (EBG) structure under the radiating element [12]-[13]. More compact textile antennas were also reported by employing the half mode of a cavity [14]-[17]. Moreover, textile antennas with circular polarization (CP) [18]-[19] and dual-band operation [20]-[22] were investigated for off-body wearable applications. To collect information effectively from sensors distributed over the body, the antenna should also operate in an on-body mode and ideally exhibit an omni-directional radiation pattern. To date, only a few antennas for on-body communication have been reported. In [23], an EBG loaded omni-directional textile antenna was proposed, but it suffers from large size (about 2 wavelengths in diameter) and a probe-feed that is difficult to implement in practice. In [24], omni-directional radiation was achieved by exciting a higher-order mode of a patch antenna. However, a multi-layer structure is required, and the antenna suffers from a low efficiency (only about 40%). In [25]-[26], dual-mode (on-body and off-body) wearable antennas were realized for different frequency bands, respectively. Dual-Polarized Embroidered Textile Armband Antenna Array with Omni-Directional Radiation for On-/Off-Body Wearable Applications Chun-Xu Mao, Member, IEEE, Dieff Vital, Student Member, IEEE, Douglas H. Werner, Fellow, IEEE, Yuhao Wu, and Shubhendu Bhardwaj, Member, IEEE B