Compact Microstrip-Based Textile Antenna for 802.15.6 WBAN-UWB with Full Ground Plane

Hindawi International Journal of Antennas and Propagation Volume 2019, Article ID 8283236, 12 pages https://doi.org/10.1155/2019/8283236 Research Article Compact Microstrip-Based Textile Antenna for 802.15.6 WBAN-UWB with Full Ground Plane Purna B. Samal ,1 Ping Jack Soh ,2 and Zahriladha Zakaria 3 1 Electronics and Communication Engineering Department, College of Science and Technology, Rinchending, Phuentsholing, Bhutan Advanced Communication Engineering (ACE) Centre of Excellence, School of Computer and Communication Engineering, Universiti Malaysia Perlis (UniMAP), Pauh Putra Campus, 02600 Arau, Perlis, Malaysia 3 Centre for Telecommunication Research and Innovation (CeTRI), Faculty of Electronic and Computer Engineering, Universiti Teknikal Malaysia Melaka (UTeM), 76100 Melaka, Malaysia 2 Correspondence should be addressed to Purna B. Samal; Received 17 October 2018; Revised 12 January 2019; Accepted 21 January 2019; Published 25 March 2019 Academic Editor: Paolo Baccarelli Copyright © 2019 Purna B. Samal et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The paper presents the design and investigation of a flexible all-textile antenna operating in the wireless body area network (WBAN) ultrawideband (UWB) specified by the IEEE 802.15.6 standard. The proposed antenna features an innovative and compact UWB radiator on top of the overall structure with a full ground plane on its reverse side. The radiator, which is based on a microstrip patch combined with multiple miniaturization and broadbanding methods, resulted in a simple topology and a compact size of 39 mm × 42 mm × 3 34 mm (0 51 × 0 55 × 0 043λ). In comparison to the literature, the proposed structure is considered to be the most compact microstrip-based textile UWB antenna to date featuring a full ground plane. The choice of the commercial textiles is also made based on cost efficiency, ease of accessibility, and ease of fabrication using simple tools. Meanwhile, the full ground plane enables the antenna operation in the vicinity of the human body with minimal body coupling and radiation towards it, ensuring operational safety. Besides its operation in the mandatory channels of the WBAN-UWB low and high bands, the proposed antenna also operates and preserves its performance in five other optional channels of the high band when placed on the body and under bend conditions of 30° and 60°. The proposed antenna successfully achieved the specific absorption rate below the regulated limit specified by the Federal Communications Commission. 1. Introduction The ultrawideband (UWB) technology introduced by the Federal Communications Commission (FCC) [1] requires a wide operating bandwidth of 7.5 GHz. This requirement triggered widespread research in overcoming the narrowband property of conventional planar antennas for its application. The technology provided a capability for high data rate transmission with low-power spectral densities [2, 3] as compared to a conventional wireless communication system. Due to its immense potential in body-worn communications [4], UWB technology was extended into the application of wireless body area network (WBAN). Based on the recent IEEE 802.15.6 WBAN standard [5], two mandatory UWB channels (low and high bands) can be used for operations. The low band (LB) is divided into three operating channels: 0, 1, and 2, with each channel requiring a bandwidth of 500 MHz and a total required LB bandwidth of 1.5 GHz operating from 3.24 to 4.74 GHz. Channel 1 is the mandatory channel in LB with its operation centered at 3.99 GHz. The high band (HB) consists of eight operating channels from Channel 3 to Channel 10. Similar to LB, each channel requires a bandwidth of 500 MHz, with a total operating bandwidth of 3.99 GHz (from 6.24 GHz to 10.23 GHz). The mandatory channel in HB is Channel 6 centered at 7.99 GHz. WBAN provides an immense potential in applications such as health monitoring [6, 7], location tracking, and emergency rescue services [8, 9]. Such applications require wireless devices to operate in close proximity to the human body, demanding a requirement for antennas that use flexible materials. This is to ensure conformance to the users’ body and ease of integration onto clothing and to guarantee 2 comfort and safety to users due to their prolonged usage near or on the body. Due to the recent introduction of commercial conductive textiles, antennas for WBAN are increasingly designed and implemented fully using textiles [10, 11]. Besides being easily integrated to clothing, the use of textiles enables a degree of transparency to the users in contrast to conventional worn electronic devices such as smart watches, loggers, trackers, and mobile devices. However, the dielectric properties of the human body poses a challenge to the full implementation of such wearable antennas, as wireless signals from these wearable antennas are very likely to be coupled to the body, resulting in inconsistent or unreliable performance. This calls for a design of textile-based wearable antennas that are not susceptible to any on-body detuning to facilitate reliable WBAN communication. One of the simplest and yet most effective method to protect the antenna against the effects of detuning caused by the human body (and vice versa) is the use of a full ground plane. Such ground planes, which need to be placed between the radiating element and the human body, are available in specific planar antenna types such as microstrip antennas. Moreover, the planar structure of the antenna is required to ensure proper integration onto the body using textile materials. However, the main limitation of this antenna type is its narrow bandwidth [12, 13], which makes it unsuitable for UWB applications. Broadbanding efforts for microstrip antennas have been previously presented, with a recent work in [14] proposing a microstrip-based UWB textile antenna based on FCC’s specifications, from 3.1 to 10.6 GHz, which resulted in minimal backward radiation. Besides its robust performance, the microstrip-based topology also provided safe specific absorption rate (SAR) values, which characterizes the level of electromagnetic absorption by tissues located in the proximity of the antennas [15]. A key factor in achieving the required UWB behavior in [14] is the combined use of various bandwidth enhancement techniques, at the expense of a relatively complex structure and large size. Inspired by [14], this paper aims to reduce the complexity of the radiating patch and overall antenna size by employing few and effective bandwidth enhancement techniques. The paper aims to achieve the antenna operation in mandatory channels of WBAN specified by IEEE 802.15.6. To our best knowledge, the proposed antenna is the one of the first microstrip-based antennas fully implemented using textil (...truncated)