Ultra-Wideband 8-Port MIMO Antenna Array for 5G Metal-Frame Smartphones

A design of an ultra-wideband eight-port multiple-input multiple-output (MIMO) antenna array in a smartphone with an open-slot metal frame for fifth-generation (5G) communications is presented. Each element is fed by a microstrip line with a tuning stub, consisting of a <inline-formula> <tex-math notation="LaTeX">$U$ </tex-math></inline-formula>-slot on the ground plane and an open slot on the metal frame. Each slot element on the ground only occupies an area of 15 <inline-formula> <tex-math notation="LaTeX">$\times $ </tex-math></inline-formula>3 mm. The antenna array can operate in 3.3–6 GHz (<inline-formula> <tex-math notation="LaTeX">$S_{11\,}< -6$ </tex-math></inline-formula> dB) that is ultra-wide bandwidth for the future 5G communications. The antenna array is manufactured and measured. Measured antenna isolation is higher than 11 dB without any decoupling structures applied. Moreover, measured radiation patterns, antenna efficiencies, and envelop correlation coefficients are also given in this paper. High agreement between the measured and simulated results is obtained, which means that the proposed antenna is promising in engineering application.