Wideband Shared-Radiator Four-Element MIMO Antenna Module for 5G Mobile Terminals

Abstract

A low-profile wideband shared-radiator four-element multiple-input multiple-output (MIMO) antenna module that can be directly and flexibly integrated with the chassis ground of a mobile terminal is proposed. The module structure of a grounded square shared patch surrounded by four corner-cut patches is constructed through the characteristic mode analysis (CMA). By analyzing the low efficiency problem caused by the reverse currents, the off-diagonal feed positions are proposed to enhance the efficiency. The use of the shared patch with four I-shaped slots and the off-diagonal feeds makes the dimension of the proposed four-element antenna module only $30\times 30\times $ 2 mm3. With the help of multiple regionalized characteristic currents and four grounded short branches, the proposed antenna module shows good simulated isolations of better than 12.5 dB in the −6 dB impedance operating band of 4.25–5.13 GHz. To verify the integration flexibility, an $8\times $ 8 MIMO antenna prototype with two proposed modules directly deployed on a phone-size chassis ground was fabricated and measured. The experimental results indicate that the −6 dB impedance operating band can cover the fifth-generation (5G) N79 band (4.4–5 GHz) with isolations of better than 10 dB and efficiencies of 40.3%–48.5%. The diversity performance, the channel capacity, the effects of the user's hands and head on the antenna performance, and the specific absorption rate (SAR) are analyzed, and the results are acceptable. With the advantages of zero clearance, small size, wide bandwidth, isolation adjustment flexibility, and integration flexibility, the proposed antenna module is potentially applicable in future mobile terminals.