DESIGN AND STUDY OF ISOLATION TECHNIQUES FOR MIMO ANTENNAS IN 5G APPLICATIONS

Abstract

This doctoral research presents a comprehensive investigation into the design, optimization, and implementation of advanced Multiple-Input Multiple- Output (MIMO) antenna systems for 5G wireless communication networks and beyond. The study addresses critical challenges in modern antenna design, including mutual coupling reduction, isolation enhancement, bandwidth expansion, gain improvement, and frequency reconfigurability, while maintaining compact form factors suitable for next-generation mobile devices and base stations. The research begins with a systematic review of wireless technology evolution, 3GPP's standardization role in 5G, and fundamental MIMO system principles. A thorough state-of-the-art analysis identifies key research gaps in antenna performance metrics and reconfiguration techniques, establishing the foundation for the proposed innovative solutions. The thesis progresses with the development of a circularly polarized, closely spaced two-port MIMO antenna optimized for 5G mid-band applications. The design integrates decoupling circuits and metasurfaces to improve isolation and performance. Extensive simulations and experimental validations confirm the antenna’s effectiveness in terms of S-parameters, gain, and radiation patterns, with comparative analyses highlighting its advantages over existing models. Further advancements include a metasurface-based ultra-wideband (UWB) four-port MIMO antenna targeting 5G mm-Wave communication within the FR2 spectrum (n257–n261). The research details unit cell design, polarization conversion mechanisms, and circular polarization characteristics. Fabrication and measurements validate the antenna’s superior gain and bandwidth, demonstrating its potential for next-generation wireless systems. Additionally, the thesis presents a closely coupled frequency- reconfigurable two-port MIMO antenna designed for 5G NR bands n48 and n78, incorporating PIN diodes to achieve dynamic frequency tuning. The self-isolation mechanism in a two-port MIMO configuration is further explored, eliminating the need for external decoupling structures while maintaining high isolation and low v mutual coupling. The design's performance is extensively validated through simulations, fabrication, and benchmarking against contemporary models. A metasurface-based frequency-reconfigurable two-port MIMO antenna is also introduced, integrating a metasurface reflector to enhance isolation and gain. The findings of this research contribute significantly to the field of MIMO antenna design for 5G applications, offering innovative solutions for improved isolation, gain, bandwidth, and frequency reconfigurability. The proposed designs demonstrate advancements in polarization control, mutual coupling reduction, and frequency agility, paving the way for future high- performance wireless communication systems. The comparative analyses against existing models establish the superiority of the proposed antennas, ensuring their suitability for next-generation 5G and beyond communication networks.