A sub-6 GHz four-element MIMO antenna using slotted metamaterial structures with low SAR performance

Abstract

A four-element multiple-input multiple-out (MIMO) antenna employing a metamaterial (MMT)-based structure is presented for sub-6 GHz wireless applications. The antenna is fabricated on an FR4 substrate and operates over the 5.7–5.9 GHz band, centred at 5.8 GHz. The overall antenna size is 46 × 44 × 1.6 mm3 (0.89λ0 × 0.85λ0 × 0.03λ0 at 5.8 GHz). Inherent decoupling is achieved through the orthogonal placement of the antenna elements, while the integrated MMT structure further suppresses mutual coupling and enhances radiation efficiency. Both simulated and measured results show good agreement, confirming reliable antenna performance across the intended frequency range. The proposed design achieves a maximum gain of 4.4 dBi, with isolation better than 24.5 dB. MIMO diversity characteristics are evaluated using envelop correlation coefficient (ECC), diversity gain (DG), Total active reflection coefficient, and channel capacity loss (CCL), an ECC below 0.001, a DG close to 10 dB, and a CCL below 0.5 bits s−1 Hz−1. User safety is assessed through specific absorption rate (SAR) analysis using a female hand phantom at 17 mW input power, demonstrating a reduction in SAR from 1.493 W kg−1 to 1.295 W kg−1 with the MTM, suitable for handheld devices.