Small Size and High Isolation MIMO Antenna System for 5G Mobile Terminals

Multi-input multi-output (MIMO) technology has been popularized in 5th-generation (5G) mobile terminals. In this paper, we design an
$8\times 8$
MIMO antenna with 4 antenna units. The working frequency band is 3.4-3.6GHz. The antenna system has merits of small volume and high isolation. The height of the antenna unit is less than 5mm, and the is less than 21mm. In the working frequency band of 3.4-3.6GHz, the isolation between any two antennas is less than - 23dB. The design of each antenna unit is based on the principle of differential mode/common mode (CM/DM) antenna. We fold the antenna inward to increase the length of current path to miniaturize the antenna. In addition, we adjust the feed structure of CM antenna to improve the isolation inside antenna units. At last, we add the defected ground structure (DGS) to antenna array, which improve the isolation between antenna elements by 8dB. According to the simulation results, we can conclude the method proposed by us is effective.