A Compact MIMO Array Antenna with Wideband Circular Polarization Using Magneto-Electric Dipole Elements for Millimeter-Wave Applications

This paper presents a miniaturized quad-port circularly polarized (CP) MIMO antenna, utilizing magneto-electric (ME) dipole array elements. The suggested antenna element design originates from a linearly polarized (LP) ME-dipole, using a narrow horizontal slot for feeding. Within this setup, the four rectangular microstrip patches function as electric dipoles, while the shorted patches create a current loop that generates a magnetic dipole. Later, the patch widths are adjusted, and a pair of symmetrical Γ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\varvec{\Gamma }$$\end{document}-shaped strips and vertical slots are introduced to attain elliptical polarization. The transition from Γ\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\varvec{\Gamma }$$\end{document}-shaped strips to the graceful curves of F-shaped strips onto the patches redirects currents, giving rise to CP ME-dipole modes, where electric and magnetic currents operate in tandem. To enhance the antenna’s axial ratio (AR), two additional vertical slots are introduced onto the ground plane feeding slot. By using this CP ME-dipole element, a four-port MIMO array antenna is constructed where four sequentially rotated 2×2\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$\varvec{2 \times 2}$$\end{document} CP array have been used. The proposed antenna ultimately attains a remarkable 28.6% impedance bandwidth, with a measured 3 dB AR bandwidth of 21% (28.1–34.7 GHz), 12.2 dBic peak gain and below -25 dB mutual coupling. The exceptional performance and compact design of this CP MIMO array antenna make it a promising choice for mmWave communication.