Abstract
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 × 0.33 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> × 0.14 λ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> , 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 |S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">11</sub> | <; -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%).
Highlights
The Yagi-Uda antenna, initially proposed by Uda [1], exhibits the advantages of high front-to-back ratio (FBR), high gain, and directive radiation pattern
Three -shaped metal plates are introduced for each antenna element, which serve as directors to tilt or steer away the radiation beam, so that the pattern diversity is achieved
Based on the three-port MIMO patch antenna with three shorting posts, a novel -shaped metal plate as a director is designed and introduced for each element, in order to achieve better spatial pattern diversity and obtain good isolation / low envelope correlation coefficient, which is strongly affected by the radiation pattern and polarization of each unit-cell
Summary
The Yagi-Uda antenna, initially proposed by Uda [1], exhibits the advantages of high front-to-back ratio (FBR), high gain, and directive radiation pattern. A five-element top-hat monopole Yagi antenna was designed and proposed in [12], achieving vertically polarized endfire radiation pattern at UHF band.
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