This article proposes a compact microstrip four-port dual circularly polarized (CP) multiple-input multiple-output (MIMO) antenna with polarization diversity for Sub-6G band. The proposed MIMO antenna consists of four antenna elements, two of which are left-hand circular polarization (LHCP), and the other two are right-hand circular polarization (RHCP). The circular polarization of each antenna element of the MIMO antenna is achieved by a microstrip feed line and a slotted ground plane with two rectangular strips. A novel decoupling element of the antenna composed of I-shaped and II-shaped metal strips is cross-connected and merged between the ground planes of the antenna to obtain wide axial ratio bandwidth and high isolation. The size of the proposed antenna is 55×55×1.6 mm3. The antenna of the impedance bandwidth (S11 ≤ -10 dB) is 3.28-3.80 GHz (14.6%), and the axial ratio bandwidth (AR ≤ 3 dB) is 2.85-3.87 GHz (30.3%). Inter-element isolation less than -16 dB and the envelope correlation coefficient (ECC) less than 0.07 are achieved between the ports of the antenna. The proposed MIMO antenna achieves full coverage of CP characteristics within the impedance bandwidth. The proposed antenna is beneficial to the application of Sub-6G band. At the same time, it is also suitable for dual circular polarization communication and polarization diversity system.
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