In this paper, a reconfigurable patch antenna with Circular Polarization (CP) diversity with theoretical discussion and verification is proposed for the fifth generation (5G) of mobile communication systems. The proposed antenna contains two PIN diodes, which are correctly placed on the ground plane to attain polarization diversity. By switching between two ON/OFF modes in the PIN diodes, the proposed antenna can support the RHCP mode or the LHCP mode. An antenna with the well-matched impedance bandwidths (S11 ≤ -10 dB) of 2.5 GHz (27~29.5 GHz) and 3 GHz (36~39 GHz) and the dual-band 3-dB axial ratios of 6% (27.3-29 GHz) and 8.4% (35-38.2 GHz) operates at both the RHCP and LHCP modes. The experimental result shows that the proposed antenna has a circular polarization bandwidth at the center frequencies of 28 and 38 GHz for both the RHCP and LHCP.
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