A new antenna design methodology based on performance analysis of MIMO and defining novel antenna parameters

Abstract

The rapid growth of wireless technology has created a significant demand for the design of Multiple-Input Multiple-Output (MIMO) antennas for wireless devices. MIMO antennas play a crucial role in meeting the requirements of current and future wireless standards, as they can maximize data rates in wireless communication systems by utilizing multiple channels within the same bandwidth. However, designing MIMO antennas for compact devices presents considerable challenges. The limited space between antennas leads to increased coupling and high correlation, which can negatively impact their performance. To address these challenges, this thesis proposes a new antenna design methodology based on MIMO performance metrics and defining antenna parameters. Existing metrics for conventional antenna systems are insufficient for fully assessing MIMO antenna performance. This methodology provides a systematic approach to optimize antenna configurations, mitigate mutual coupling, and achieve desired performance characteristics, paving the way for enhanced system capacity. The thesis introduces a novel methodology for designing MIMO antennas that relies on crucial performance metrics and defining parameters. These parameters include factors such as antenna spacing, slot dimensions, strip placements, and parasitic element sizes, which are important for meeting the requirements of modern wireless standards within the LTE and sub-6 GHz 5G bands. The research presents five distinct MIMO antenna designs, each optimized for specific requirements and validated through simulations and experimental measurements. Firstly, the dual-band Vivaldi-shaped MIMO antenna covers the 5G NR bands n78 and n79, boasting gains of over 7.63 dBi and 8.5 dBi respectively, while maintaining mutual coupling below -30 dB. Secondly, the concentric octagonal-shaped MIMO antenna is designed for 5G UE applications in the n38 band, achieving a gain of over 5 dBi and mutual coupling below -25 dB. Thirdly, the compact quad-element MIMO antenna is designed for LTE/Wi-Fi applications, exhibiting high isolation exceeding 17 dB and a channel capacity loss lower than 0.6 b/s/Hz. Fourthly, the wideband MIMO antenna is a single-element design with quad-ports, operating in the 2.1/2.3/2.6 GHz and 2.4 GHz bands. It offers an operating bandwidth of 2-3.0 GHz, reflection coefficients below -10 dB, isolation under -25 dB using synthesized pi-networks TL-based decoupling network, and a diversity gain of approximately 10 dB. Finally, a quad-element MIMO antenna utilizing a modified Apollony fractal, designed for 5G wireless communications, achieves S11 below or equal to -10 dB within the impedance bandwidth, with low mutual coupling below -20 dB. The thesis explores various decoupling strategies to mitigate mutual coupling and enhance antenna performance. These strategies include antenna placement and orientation, parasitic elements, neutralization, and synthesized Pi-networks TL-based decoupling network topology. Each design is thoroughly evaluated through simulations and experimental measurements, with performance metrics including S-parameters, envelope correlation coefficient (ECC), channel capacity, total active reflection coefficient (TARC), and diversity gain. The research demonstrates the feasibility and effectiveness of the proposed methodology for designing compact MIMO antennas that offer improved performance metrics, making them well-suited for use in 5G and beyond wireless communication systems.