Design of a Twelve-Port MIMO Antenna System for Multi-Mode 4G/5G Smartphone Applications Based on Characteristic Mode Analysis

This paper presents a twelve-port multiple-input multiple-output (MIMO) antenna system for multi-mode 4G/5G smartphone applications. Characteristic mode analysis (CMA) is used to illustrate the operation principle and optimize the geometrical structure of the antenna system. The proposed MIMO antenna system consists of a 4G antenna module and a 5G antenna module. The 4G antenna module is a $2\times 2$ MIMO antenna array capable of covering the LTE700/2500/3400, GSM850/900, DCS, PCS, UTMS, 2.4-GHz WLAN, and 3.5-GHz WiMAX, which consists of two symmetrical antenna elements, and uses protruded ground to improve the isolation between the two adjacent 4G module antenna elements. The 5G antenna module is a $10\times 10$ MIMO antenna array composed of ten identical monopole antennas and operates at the bands of $3.31\sim 3.70$ GHz and $4.46\sim 5.40$ GHz, covering the 3.5-GHz band ($3.4\sim 3.6$ GHz) and 4.9-GHz band ($4.8\sim 5.0$ GHz) for 5G applications. The proposed antenna is fabricated, and the experimental results agree with the simulated results well. The calculated envelope coefficient correlation is lower than 0.5, indicating that the diversity performance meets the need of the MIMO antenna system. All the features make the antenna suitable for multi-mode 4G/5G smartphone applications.