A low-profile wideband 8-antenna array for future 5G New Radio (5G NR) mobile devices is studied. Each array element has a size of 16.85 mm × 4.6 mm, and the height of the frame is only 5 mm. The array element is composed of a driven element coupled-fed by a T-shaped feeding element and a shorting element. The driving element and the shorting element enable the antenna to obtain dual resonance modes, while the T-shaped feeding structure can improve the impedance matching. The 10-dB impedance bandwidth (3.27–4.24 GHz) of the proposed 8-antenna array can completely cover the 5G Sub-6GHz NR Band n77/n78. The measured antenna efficiency of each array element was higher than 50%. Good isolation of >13 dB was achieved between adjacent array elements due to the introduction of a modified decoupling structure. Besides achieving a desirable ECC of <0.06, the calculated channel capacities of the 8 × 8 multiple-input multiple-output system working across the bands of interest can reach up to 38.8 bps/Hz.