High-isolation eight-element MIMO array for unbroken metal-rimmed smartphone applications

ABSTARCT In this paper, a high-isolation eight-unit multiple-input multiple-output (MIMO) array is proposed, which applies to future smartphones with unbroken metal frames. Two types of elements (inverted H-shaped slot antenna [IHSA] and modified top-loaded monopole [MTLM]) are adopted to realize low mutual coupling, and the detailed decoupling mechanism is also presented. The IHSA with a better-reduced ground effect is utilized, which contributes to suppressing mutual coupling. To further enhance isolation, the MTLM without ground clearance is exploited, which cannot excite the radiated mode of the IHSA. To mitigate the effects of an unbroken metal frame, a shorting strip is introduced, which not only improves the impedance matching but also reduces the profile of the MTLM. Ultimately, the proposed MIMO system integrated with an unbroken metal frame is constituted by four IHSAs and four MTLMs, which offers a measured isolation of more than 20 dB. What's more, the calculated envelop correlation coefficients (ECCs) are less than 0.013.