Wideband Circularly Polarized Textile MIMO Antenna for Wearable Applications

In this paper, a wideband circularly polarized (CP) textile multiple-input-multiple-output (MIMO) antenna is presented for wearable applications. The designed MIMO antenna consists of two sickle-shaped resonating elements and a common ground plane. Each antenna element is excited by a microstrip line feed, and an inverted L-shaped strip is introduced in the ground plane to support circular polarization. The antenna covers impedance bandwidth ( $\text{S}_{11}\le -10$ dB) of 3.6–13 GHz and 3-dB axial ratio bandwidth (ARBW) of 5.2–7.1 GHz. The proposed textile MIMO antenna exhibits envelope correlation coefficient (ECC) < 0.02, diversity gain (DG) $>9.96$ , total active reflective coefficient (TARC) $ < -10$ dB, channel capacity loss (CCL) < 0.2 b/s/Hz, and mean effective gain (MEG) ratio within ±0.5 dB. The antenna offers dual-sense circular polarization and high isolation (>18) between the resonating elements. Also, the proposed antenna is investigated for different human body situations, and its specific absorption rate (SAR) for human tissues specimen is studied. The overall size of the proposed CP textile MIMO antenna is $32.5 \times 42 \times 1$ mm3. The designed MIMO antenna could be useful for wearable applications due to its textile layers, reasonable on-body performance, and compact size.