Eighteen-Element Antenna for Metal-Rimmed Smartphone Sub-6 GHz LTE42 Band Applications

Due to the limited space and large mutual coupling levels, the design of sub-6 GHz massive Multi-Input Multi-Output (m-MIMO) smartphone antenna system attracts antennas’ designers and engineers worldwide. Therefore, this paper presents 18-element m-MIMO antenna system that covers the long-term evolution 42 (LTE42) frequency band (3.4–3.6 GHz) for the fifth generation (5G) applications in metallic frame smartphones. The proposed array system is etched on the long sides of a metal rim of the mobile chassis symmetrically, which is electrically connected to the system ground plane with zero ground clearance. A low-profile frame of height 7 mm (λ/12.3) is symmetrically placed below & above the ground system level. The two frame parts (above/ below the ground level) are utilized separately for the implantation of the antenna elements to achieve good space exploitation and perfect pattern diversity between elements. Orthogonal feeds are used to further increase the level of the isolation where each antenna element above the ground level is fed by a 50-ohm microstrip line, and each antenna element below the ground level is fed by a 50-ohm coplanar waveguide (CPW). The proposed antenna structure is a capacitive coupled-fed open-slot antenna with a small footprint area of 12 × 3.5 mm2 (λ/7.2 × λ/24.5, where λ represents the free space wavelength at 3.5 GHz). A small coupling L-shaped strip provides a capacitive coupling for the proposed 5G antenna structure. To establish the contribution of the proposed 18-element m-MIMO, the prototype of the proposed system was manufactured and successfully measured. Both measured and simulated results are shown to be in good agreement. This proves that the proposed antenna provides coverage for the LTE42 band (3.4–3.6 GHz) with acceptable isolation and efficiency. Moreover, the performance of the proposed m-MIMO were further verified via channel capacity calculation and the envelope correlation coefficient (ECC) measurement. Based on that, the proposed m-MIMO is shown to provide a desirable performance for all m-MIMO parameters while it owns the largest MIMO order in mobile terminals in the open literature.