In this paper, a compact quad-port multiple-input multiple-output (MIMO) antenna based on magneto-electric (ME) dipole elements has been developed for Ka-band applications with circular polarization (CP) characteristics. Four \({\textbf {2}} \times {\textbf {2}}\) arrayed aperture-coupled ME-dipole elements fed by four T-shaped power divider networks are sequentially rotated to enhance isolation. The implementation of two vias on the ME-dipole segment forms an induced magnetic current loop, generating a magnetic dipole at a certain phase, while the two constricted F-shaped patches form an electric dipole segment with a \({\textbf {90}}^\circ \) phase difference, generating a CP sense. A Z-shaped aperture on the ground plane of each element is adjusted to enhance the 3 dB axial ratio bandwidth (ARBW) and suppress the flow of current from one port to another, improving port isolation by \(-\) 25 to \(-\) 40 dB. Validation of the fabricated prototype, sized \({\textbf {1.9}}\lambda _g\times {\textbf {1.9}}\lambda _g\times {\textbf {0.17}}\lambda _g\) , demonstrates a \(-\) 10 dB impedance bandwidth (IBW) of 42.4%, an ARBW of 17.9%, and a peak realized gain of 10–13.5 dBic.
