Metamaterial-Based Structures for Mutual Coupling Reduction Technique and Performance Enhancement in 5G Smartphone MIMO Antennas: A Systematic Review. - Noptin Harpawi; Muzammil Jusoh; Mohamed Nasrun Osman; Emansa Hasri Putra; Thennarasan Sabapathy; Akram Alomainy (IEEE Access, 2026)