Metamaterial-based two element MIMO array design for wireless portable devices

In this work, we present a metamaterial-based approach to enhance isolation in a dual-element circular patch multiple-input multiple-output (MIMO) antenna operating at 5.5 GHz. The proposed metamaterial unit cell has a compact size of 4×5.8 mm2 and is designed on a low-cost FR-4 substrate with a height of 1.6 mm. In MIMO configuration, two radiating elements separated by 10 mm exhibit an isolation level of 19.7 dB. To mitigate inter-element coupling, an eight-cell metamaterial slab is printed between patch elements, improving isolation to 24.3 dB by suppressing waves and minimizing near-field coupling. The antenna is excited via a conventional microstrip feed, which is subsequently modified to a stepped feed structure to achieve frequency reconfiguration. However, this shifts the resonant frequency to 5.7 GHz, achieving compatibility with WLAN bands. The performance of the proposed MIMO antenna is evaluated and the simulation results demonstrate a low envelope correlation coefficient, improved gain, and suppression of mutual coupling. Due to these attributes, the proposed design demonstrates suitability for wireless portable devices.