The design of an eight-port MIMO antenna at the sub-6-GHz (LTE 42/43 and 46) bandsfor fifth-generation (5G) smartphone is presented. First, based on the Babinet's principle, a microstrip slot antenna (MSA) is designed from its counterpart complementary structure, microstrip patch antenna (MPA) to operate over the LTE 46 band. In order to make the MSA to operate at the specified three LTE bands, a proposed single antenna, namely RMSA, is achieved by adding a strip-ring resonator within the grounded slot of MSA which shows a good measured impedance bandwidth (S11 ≤ -6 dB) of 3.28 ~ 3.84 GHz and 5.14 ~ > 6.0 GHz. Then, eight similar antenna elements of RMSA are printed on a smartphone printed circuit board (PCB). An FR4 substrate is used as the system PCB with an overall dimension of 80 × 150 × 0.8 mm3. Two techniques, namely polarization and pattern diversity, are exhibited by designing the MIMO system due to the orthogonal arrangement of microstrip lines feeding the RMSAs. Simulated and experimental results are conducted to examine the performance of the designed MIMO antenna. Good isolation, acceptable gain, and efficiency are obtained over the bands of interest which verify the suitability of the proposed system for MIMO smartphone applications.
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