Design of Metamaterial Loaded Wideband Sub-6 GHz 2 × 1 MIMO Antenna with Enhanced Isolation Using Characteristic Mode Analysis

This paper presents, a modified rhombus-shaped antenna designed and analyzed using characteristic mode analysis (CMA) for a sub-6 GHz range of 5G. The proposed antenna is extended to design a 2 × 1 MIMO antenna having a wide bandwidth of 2600 MHz (3.2–5.8 GHz). The high level of mutual coupling (|S21|= − 12.31 dB at 4.75 GHz) exhibited by MIMO antenna is alleviated with the help of modified hexagonal-shaped mu-negative (MNG) metamaterial unit cells. Using CMA, MNG unit cells are placed (onto MIMO antenna) such that orthogonal modes are generated within MIMO antenna elements resulting in a high isolation level (S21 <  − 25 dB) for the entire operating range of bandwidth (with peak value of − 34.4 dB at 4.75 GHz). This also aids in the miniaturization of MIMO antenna by enabling the placement of antenna elements at a minimized edge-to-edge gap of 0.13λ (where, λ is the resonating frequency). The proposed MIMO antenna with MNG unit cells (called MNG-MIMO antenna) exhibits good envelope correlation coefficient with (ECC < 0.001) and diversity gain (DG = 9.9 dB), along with a high radiation efficiency of 82% while retaining a wide-bandwidth (2600 MHz). Also, the proposed MNG-MIMO antenna exhibits circular polarization (Axial ratio < 3 dB) in the frequency range of 4.56–4.89 GHz. An eight-element MNG-MIMO antenna (called eight-element MNG-MIMO) with a ground plane of 170 × 80 mm2 is analyzed to highlight the practicality of the proposed MNG-MIMO antenna. The obtained simulated response of eight-element MNG-MIMO indicates no change in efficiency and ECC levels however a minor variation in isolation is observed. Thus with a compact volume of 990mm3, the proposed design is fit for various 5G and IoT applications.