Designs, developments, challenges, and fabrication materials for MIMO antennas with various 5G and 6G applications: a review

The rapid expansion of digital media platforms and their growing user base in the wireless industry necessitate communication systems to provide information at high speeds with reliable connections. Therefore, wireless communication systems with a single antenna cannot accomplish these requirements. Consequently, the access and utilization of multi-input multi-output (MIMO) antennas are becoming more common in contemporary high-speed transmission systems. This article covers the fundamentals of MIMO antenna operation, the metrics for MIMO antenna performance parameters, and the design methodologies for specifying the three most commonly used antennas (two-port, quad-port, and eight-port). Additionally, it discusses their ability to improve channel capacity significantly. It focuses on designing MIMO antennas with ultra-wideband (UWB) for 5G systems operating between 1 and 27 GHz and millimeter-wave (mmWave) bands from 30 to 100 GHz. This article is valuable for researchers interested in developing MIMO antennas for diverse applications. It compiles advanced methods related to materials, advancements, challenges, and state-of-the-art technologies used in the design of high-performance MIMO antennas. We concluded that antennas that operate at mmWave frequencies have small dimensions and suffer from isolation problems in the MIMO formation. In contrast, antennas operating below 6 GHz are large and do not suffer from isolation problems.