Low specific absorption rate quad-port multiple-input-multiple-output limber antenna integrated with flexible frequency selective surface for WBAN applications

This paper presents the design and analysis of a multiple-input-multiple-output (MIMO) textile antenna for wireless body area network (WBAN) applications. The MIMO antenna is comprised of four identical modified rhombus-shaped monopole antenna elements of size of 0.57 λ0× 0.57λ0× 0.015λ0 , where λ0 is the wavelength calculated at the lowest operating frequency. The antenna is backed by a 6 ×6 frequency selective surface (FSS) of dimensions of 0.84 λ0× 0.84λ0× 0.015λ0 to improve gain and to reduce specific absorption rate (SAR). The antenna has an impedance bandwidth (S 11 ⩽ −10 dB) of 8.8 GHz (2.8–11.6 GHz) and isolation of >19 dB between the resonating elements. In order to assess the MIMO antenna’s flexibility, the bending analysis is performed for various bending radii. The obtained diversity metrics are: envelope correlation coefficient <0.5 dB, diversity gain <10 dB, channel capacity loss <0.4 bits s−1 Hz−1, and total active reflection coefficient <−10 dB. The performance of the antenna with and without FSS is investigated for gain enhancement and SAR reduction. With the help of FSS, the antenna gain is increased to 8.44 dBi, and the SAR reduced from 6.99 Watt kg−1 to 0.0273 Watt kg−1. The FSS achieves the highest efficiency of 96%. The designed antenna is suitable for smart textile applications due to its low SAR, high gain, and wider impedance bandwidth.