Design of an Ultra-Wideband MIMO Antenna with Open-Slot Structures for 5G Metal-Frame Smartphones

This paper presents the design and implementation of an ultra-wideband MIMO antenna for sub-6 GHz 5G metal-frame smartphones. The proposed antenna array includes four pairs, each comprising a slotted patch element and an open-slot structure on the metallic rim. The design achieves compactness by sharing the same aperture, critical for overcoming metal-frame smartphone constraints. It minimizes the required ground clearance to 40 × 0.7 mm2 to fit the limited space of metallic bezels while maintaining high inter-element isolation. Specifically, one element operates at 2.5–3.8 GHz and 4.8–7.0 GHz, while the other provides continuous coverage from 2.5 to 6.5 GHz, supporting all global sub-6 GHz 5G frequency bands. Specifically, one element operates at 2.5–3.8 GHz and 4.8–7.0 GHz, while the other offers continuous coverage from 2.5 to 6.5 GHz, supporting all sub-6 GHz 5G frequency bands. The open-slot configuration enlarges the operational bandwidth and improves isolation, achieving more than 12.6 dB isolation between elements. A prototype was fabricated and experimentally tested. Measured results indicate that the antenna array maintains a total efficiency above 56% and an envelope correlation coefficient below 0.18 across the target bands. The measured and simulated results are in good agreement, confirming the effectiveness of the proposed design. The proposed antenna is a strong candidate for next-generation 5G smartphone applications due to its wideband performance, high isolation, and compact integration.