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In this paper, a dual-band four-element multi-input and multi-output (MIMO) antenna system based on compact self-decoupled antenna pairs is proposed for the fifth-generation (5G) operation in mobile terminals. By sharing one common grounding branch for the two adjacent antenna units, dual-band antenna pairs with high isolation can be obtained. In particular, the two compact antenna pairs are placed perpendicularly on both sides of the system ground plane. The MIMO antenna system is optimized to operate in both 3.5 GHz (3.4-3.6 GHz) and 4.9 GHz (4.8-5.0 GHz) bands with isolation better than −17.5 dB for the low band and −20 dB for the high band. The proposed dual-band four-antenna MIMO system is fabricated and measured, and a good agreement between the simulation and measurement is obtained. Moreover, the influences of the phantom hand and display panel on the performance of the MIMO antenna system are also studied and discussed.INDEX TERMS 5G, MIMO system, mobile antennas, self-decoupled antenna pairs, sub-6GHz.

A multi‐antenna system based on an antenna element that has the self‐isolated property for the fifth‐generation (5G) multiple‐input and multiple‐output (MIMO) operation in mobile terminals is presented. The proposed antenna has one T‐shaped feeding element and two identical L‐shaped radiating elements and they are symmetrically located along the central line of the antenna. In particular, the two L‐shaped elements act as not only the antenna radiating element but also the decoupling element between two adjacent antenna units. It is demonstrated that very good isolation (better than 20 dB) for the 8‐antenna MIMO system can be achieved without using any additional decoupling elements or decoupling techniques. Envelope correlation coefficient (ECC) and channel capacity (CC) are also used to evaluate the MIMO performances of the proposed MIMO antenna system. Antenna prototypes are fabricated and measured; and quite good agreement between simulation and measurement is obtained.

A wideband 8-antenna multiple-input and multiple-output (MIMO) system that can cover 3.3-5.0 GHz is proposed for the 5G new radio N77/N78/N79 application in mobile phones. The wide bandwidth of the MIMO antenna system is obtained by the proposed coupled-loop antenna, which has three coupling sections located separately at its top central and two sides. Due to this special arrangement, the coupled-loop antenna can support three resonance modes of loop antenna: 0.5λ, 0.75λ, and 1.0λ modes. The distinctive feature of the proposed coupled-loop antenna design is that it can excite the 0.75λ modes, which has not been reported before. The wide bandwidth is obtained by the combination of the three resonance modes. To evaluate the performance of the proposed 8 × 8 MIMO antenna system, the antenna isolation, envelope correlation coefficient (ECC), and channel capacity (CC) are all investigated. Antenna prototypes for an 8-antenna MIMO system located along the edge of mobile phones are fabricated and measured, and; quite good agreements between simulation and measurement are obtained. INDEX TERMS 5G communication, coupled-loop antenna, mobile terminal, wideband MIMO antenna system.