Vertically Polarized Quasi-Yagi MIMO Antenna for 5G N78 Band Application

In this study, a three-port vertically polarized Quasi-Yagi Multiple-Input-Multiple-Output (MIMO) antenna system with pattern diversity is proposed for 5G N78 band application. All the three ports, which are sequentially rotated by 120°, are integrated together on a circle patch. Each antenna element is fed by a probe and an annular slot etched on the patch which works as a capacitor to counteract the inductance effect introduced by the feeding probe and the nearby shorting posts. A patch-like broadside radiation pattern is generated for each element. By introducing a novel Γ-shaped metal plate for each element, the radiation beam could be tilted and deviate from the z axis by around +30° to suit the diversity application demand. Good isolation is achieved by introducing a metal post between every two ports, which well suppresses the mutual coupling induced by the current between the ports. The working principle of the proposed MIMO antenna is theoretically illustrated in detail and experimentally verified. The Proposed antenna occupies a cylindrical volume of π × 0.33²× 0.14 λ₀³, where λ0 represents the free space wavelength at the center frequency of the operating band. The measured overlapping bandwidth covers the N78 band (3.3-3.8 GHz) with |S₁₁| <; -10 dB for the three antenna elements. The proposed antenna offers attractive features including a shared radiation aperture, pattern diversity, good isolation (≤ 20 dB) good gain (≥ 8.2 dBi), low field envelope correlation coefficient value (≤ 0.001), and high radiation efficiency (≥ 74%).