Wideband Circularly Polarized Two-Element MIMO Antenna with Polarization Diversity

This paper introduces a wideband MIMO (multiple input multiple output) antenna operating Sub 6 GHz 5G frequency band with circular polarization (CP). It comprises two identical printed monopole antennas (PMAs) with disconnected ground planes, spaced at $0:051 \lambda_{0}$ ($\lambda_{0}$ is a free-space wavelength at lowest frequency). An inverted U-shaped parasitic element reduces the mutual coupling and improves the axial ratio (AR), while a substrate cavity reflector is installed to be completely CP antenna and increase the absolute gain in the boresight direction. The proposed antenna achieves a measured 10dB impedance and 3dB AR bandwidth of 46.58% (3.03 - 4.95 GHz) with a maximum gain of 5.39 dBic. Notably, polarization in the far-field can be switched between right-hand circular polarization (RHCP) and left-hand circular polarization (LHCP) by changing the exciting port. Experimental measurements validate the antenna's performance within the desirable frequency range.