Polarization-orthogonal co-frequency dual antenna pair suitable for 5G MIMO smartphone with metallic bezels

This paper proposes a polarization-orthogonal co-frequency dual antenna pair suitable for fifth-generation (5G) multiple-input multiple-output (MIMO) smartphone with metallic bezels. The proposed spatial-reuse dual antenna pair consists of a split on the metallic bezel and a slot on the mainboard ground, where the slot is centered on the split. Two orthogonal degenerate characteristic modes operating at half wavelength including in-phase current and slot modes can be excited on the same antenna structure. An end-shorted microstrip line that crosses the split is used to excite the in-phase current mode, producing y-polarized radiation, while a symmetrical slot-centered Y-shaped feeding network with its shorted ends crossing the slot is adopted to excite the slot mode, producing x-polarized radiation. To the best of authors' knowledge, this is the first time that a co-frequency dual antenna pair suitable for smartphone with metallic bezels is proposed. A sub-6 GHz dual antenna pair operating at 3.5 GHz that occupies a footprint of 25 × 7 × 1.5 mm³ shows a simulated isolation better than -24.1 dB without any external decoupling measures and an envelope correlation coefficient (ECC) lower than 0.008. A four-antenna MIMO array is fabricated and measured to verify the feasibility. Across the operation band, the measured isolation of the antenna pair is better than -20.1 dB and other isolation levels are all better than -12.7 dB, the ECCs of any two antennas are lower than 0.13, and the total efficiency range of the four antennas is 35.2%64.7%. The proposed dual antenna pair exhibits a great potential to be applied in future 5G MIMO smartphone.