Combined RIS and EBG Surfaces Inspired Meta-Wearable Textile MIMO Antenna Using Viscose-Wool Felt

In this paper, we present a textile multiple-input–multiple-output (MIMO) antenna designed with a metamaterial inspired reactive impedance surface (RIS) and electromagnetic bandgap (EBG) using viscose-wool felt. Rectangular RIS was used as a reflector to improve the antenna gain and bandwidth to address well known crucial challenges—maintaining gain while reducing mutual coupling in MIMO antennas. The RIS unit cell was designed to achieve inductive impedance at the center frequency of 2.45 GHz with a reflection phase of 177.6^◦. The improved bandwidth of 170 MHz was achieved by using a square shaped RIS under a rectangular patch antenna, and this also helped to attain an additional gain of 1.29 dBi. When the antenna was implemented as MIMO, a split ring resonator backed by strip line type EBG was used to minimize the mutual coupling between the antenna elements. The EBG offered a sufficient band gap region from 2.37 GHz to 2.63 GHz. Prior to fabrication, bending analysis was carried out to validate the performance of the reflection coefficient (S₁₁) and transmission coefficient (S₂₁). The results of the analysis show that bending conditions have very little impact on antenna performance in terms of S-parameters. The effect of strip line supported SRR-based EBG was further analyzed with the fabricated prototype to clearly show the advantage of the designed EBG towards the mutual coupling reduction. The designed MIMO-RIS-EBG array-based antenna revealed an S₂₁ reduction of −9.8 dB at 2.45 GHz frequency with overall S₂₁ of <−40 dB. The results also indicated that the proposed SRR-EBG minimized the mutual coupling while keeping the mean effective gain (MEG) variations of <3 dB at the desired operating band. The specific absorption rate (SAR) analysis showed that the proposed design is not harmful to human body as the values are less than the regulated SAR. Overall, the findings in this study indicate the potential of the proposed MIMO antenna for microwave applications in a wearable format.