Millimeter-Wave Yagi MIMO Antenna With High Isolation and Beam-Tilting Capability Using Optimized Metamaterials

A high-performance multiple-input–multiple-output (MIMO) antenna for the millimeter-wave spectrum is introduced in this paper, featuring broadband performance, high gain, superior isolation, and beam-tilting functionality. A single Yagi antenna, utilizing a third-order mode dipole as its driver with integrated reflectors, is designed for the 28 GHz band to enhance gain. The rigorous numerical optimization procedure was employed to precisely adjust the dimensions and positions of the driven dipole, director, and reflectors. The optimized Yagi antenna functions within the 28 GHz 5G band, offering a 2.6 GHz bandwidth. The radiation pattern results reveal that the antenna’s gain in this higher resonant mode exceeds that of a conventional Yagi-Uda antenna, achieving a gain of 9.35 dBi at 28 GHz. The MIMO antenna is subsequently designed using two adjacent Yagi elements, with a metamaterial array positioned between them to enhance isolation and tilt the radiation beam. The trust region (TR) method is utilized to refine the metamaterial’s dimensions, achieving up to 58 dB of isolation at 28 GHz. Additionally, the metamaterial enables a 33-degree E-plane beam tilting relative to the end-fire direction when switching between the two ports’ excitations. The system is validated through experiments, demonstrating a strong correlation between the simulated and measured data.