Metamaterial and Metasurface Techniques for Mutual Coupling Reduction in MIMO Antennas: A Comprehensive Review (2019-2025)

Abstract

The performance of Multiple-Input Multiple-Output (MIMO) antennas—essential to 5G and evolving 6G communication systems—is often limited by electromagnetic interaction between closely spaced radiating elements. Over recent years, met-amaterials (MTMs) and metasurfaces (MTSs) have shown remarkable potential in suppressing such mutual coupling while maintaining compactness and efficiency. This paper presents a detailed review of 18 significant contributions published between 2019 and 2025, systematically classifying them into superstrate-based designs, defected ground structures, resonator/CSRR con-figurations, hybrid MTM-SIW approaches, massive-MIMO scaling, and reconfigurable MTM techniques. Reported isolation improvements range between 20–50 dB with varying trade-offs in gain, bandwidth, and fabrication complexity. The paper also summarizes substrates and design choices commonly adopted across sub-6 GHz, mm Wave, and THz applications. Finally, it discusses key research gaps and emerging directions such as AI-assisted MTM synthesis, integration with reconfigurable intelli-gent surfaces (RIS), and sustainable material adoption for future wireless devices.

Introduction

Modern communication networks rely on MIMO antennas for high data rates, reliability, and spectral efficiency. As antenna arrays shrink to fit compact wireless devices, mutual coupling between closely spaced elements becomes a major challenge, degrading isolation, radiation patterns, and system performance. Conventional decoupling approaches (neutralization lines, orthogonal layouts, DGS) offer partial relief but often compromise bandwidth or increase design complexity. Metamaterials (MTMs) and metasurfaces (MTS) provide a promising alternative by enabling surface-wave suppression and electromagnetic field control without significant size penalties. This paper builds on earlier work by the authors (2018) and reviews MTM/MTS-based coupling-reduction techniques published from 2019–2025.

A systematic literature survey across major databases shortlisted 18 relevant studies based on criteria such as experimental validation, MTM/MTS involvement, and reporting of S-parameters, ECC, bandwidth, or gain metrics. These works were grouped into six categories: superstrate loading, DGS–MTM integration, CSRR-based resonators, hybrid SIW methods, massive-MIMO MTM arrays, and miniaturized/reconfigurable MTMs.

The review shows that metasurface superstrates deliver strong isolation (25–41 dB) for sub-6 GHz systems but may add thickness. DGS–MTM hybrids provide broad applicability from sub-6 GHz to mmWave with isolation around 22–32 dB, although fabrication precision is crucial. CSRR decouplers achieve the highest isolation (up to 50 dB at THz) but remain narrowband. Hybrid SIW and MTM tiling approaches scale effectively for massive-MIMO arrays, while compact MTMs support IoT and wearable applications.

Comparative analysis highlights consistently low envelope correlation coefficients (ECC < 0.05), indicating strong diversity performance across techniques. Despite these advances, the study is theoretical and draws exclusively from published data; student-level fabrication of MTMs remains difficult due to cost and material constraints. Simulation using open-source EM tools is a practical next step.

Conclusion

Metamaterial and metasurface innovations have transformed the landscape of mutual coupling reduction for MIMO systems. Through this comprehensive analysis (2019–2025), it is evident that these engineered materials provide versatile and scalable path-ways to high isolation and diversity. As wireless systems progress toward 6G, MTM/MTS structures will remain central to achieving compact, energy-efficient, and adaptive antenna arrays.

References

[1] Al-Bawri, S.S., et al., “Massive metamaterial system-loaded MIMO antenna array with high isolation,” Electronics / PMC, 2022 — Demonstrates MTM arrays for large MIMO decoupling (up to ~32 dB). [2] Hasan, M.M., et al., “Gain and isolation enhancement of a wideband MIMO antenna using metamaterial loading,” Sensors / MDPI, 2022 — Practical MTM-loaded MIMO design with measured diversity metrics (ECC, CCL). [3] Islam, T., et al., “Mutual coupling reduction in compact MIMO antenna using decoupling structures,” Micromachines / MDPI, 2023 — Shows parasitic/decoupling patch and MTM strategies achieving <-32 dB coupling. [4] Jafargholi, M. & Jafargholi, A., “Mutual Coupling Reduction in an Array of Patch Antennas Using CLL Metamaterial Superstrate for MIMO Applications,” (conference / journal record) — Classic CLL-superstrate approach and comparative results. [5] Si, L., et al., “Broadband extremely close-spaced 5G MIMO antenna with a metamaterial-inspired superstrate,” Optics Express, 2019 — Introduces dual-layer MTM superstrate for broadband coupling suppression. [6] Mark, R., “Isolation and Gain Enhancement Using Metamaterial Superstrate,” Radioengineering, 2019 — Early experimental demonstration of MTM superstrate improving both gain and isolation. [7] Mark, R., et al., “Mutual coupling reduction using near-zero ? and ? metamaterial superstrate,” IET Microwaves, Antennas & Propagation, 2020 — Uses NZE/NZM superstrate to reduce coupling in patch arrays. [8] Wu, T., et al., “Decoupling of MIMO antenna array based on half-mode substrate integrated waveguide (HMSIW),” Journal / ScienceDirect, 2022 — HMSIW + MTM hybrid decoupling technique for compact arrays. [9] Khan, D., et al., “Dual-band 5G MIMO antenna with enhanced isolation using metamaterials,” Scientific Reports, 2024 — Miniaturized dual-band MIMO for mmWave with MTM decoupling. [10] Rahman, M.A., et al., “Metamaterial-based tri-band compact MIMO antenna,” Scientific Reports / Nature, 2025 — Recent tri-band MTM MIMO module for microwave/mmWave with practical measurements. [11] Din, I.U., et al., “A Novel Compact Metamaterial-Based Four-Element MIMO Antenna for 5G mmWave,” Wiley / Advances, 2024 — 4-element MTM MIMO design with wide operating band and isolation improvements. [12] Musaed, A.A., et al., “High-isolation 16-port massive MIMO antenna based on metamaterials,” PMC article, 2024 — Massive-MIMO scale MTM loading and measured isolation results. [13] Hasan, M.M., et al., “Metamaterial-loaded miniaturized extendable MIMO antenna (4/8 elements),” ScienceDirect, 2024 — MTM loading for miniaturization plus extendable array topologies. [14] Raza, M.U., et al., “Metasurface-assisted mutual coupling suppression in patch arrays using CLL superstrate,” ScienceDirect / Composite Materials / Antennas, 2024 — CLL metasurface superstrate applied to patch arrays for MIMO. [15] Islam, M.T., et al., “Applications of metamaterials in antennas and mutual coupling suppression,” Scientific Reports, 2021 — Review-style paper covering MTM uses including coupling suppression. [16] Song, Z., “High-Isolation Compact MIMO Antenna with CSRRs,” PIER / Journal, 2024 — CSRR etched patches for simultaneous miniaturization and isolation gain. [17] Khan, F., Khajeh-Khalili, F., “A simple method to enhance gain & isolation of MIMO antennas based on metamaterial structures (mmWave),” Journal, 2021 — mmWave MTM+defected ground approaches for gain/isolation improvements. [18] Al-Bawri, S.S., et al., (other PMC review) “Massive metamaterial system-loaded MIMO antenna array” — Good for large array decoupling techniques and practical implementation notes.

Copyright

Copyright © 2025 Priyanka Nayak, Komal Dudam. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.