## 1 Introduction
One notable example is the 5G-compatible MIMO antenna presented in reference [16]. This design operates at 28 GHz and features a unique \"infinity-shaped\" structure incorporating three circular rings. This design aimed to enhance performance at high frequencies and demonstrated an antenna radiation efficiency of 92% and a peak gain of 6.1 dBi. A notable improvement in this field is the MIMO antenna with a \"tree-like\" configuration proposed in [17]. Tailored for 5G systems, this design integrates four curved radiating elements to achieve broad bandwidth coverage. Its radiation patterns are characterized at operational frequencies of 28 GHz, 33 GHz, and 38 GHz, demonstrating peak gains of 10.58, 8.87, and 11.45 dBi, respectively. The work in reference [18] presents an MIMO antenna optimized for dual-band 28/38 GHz operation, delivering high-gain performance. This configuration achieves peak realized gains of 4.15 dBi and 7.73 dBi at the respective frequencies, with total efficiencies reaching 80.13% and 85.44%. Furthermore, an MIMO antenna comprising a crescent-shaped slot elliptical operating at dual frequencies (28/38 GHz) was introduced in reference [19]. Utilizing a linear array of 1 \(\times\) 4 elements, this design achieved a bandwidth of 7.8 GHz and peak gain of 10.4 dBi. Reference [20] presents an implementation that achieves high isolation (up to 23 dB) between MIMO antenna elements by employing spatial and polarization diversity. This antenna operates across the 27.25-29 GHz and 34.5-41 GHz frequency bands, achieving gains of 9.5 and 11.7 dBi at 28 and 38 GHz, respectively. Reference [21] introduced an MIMO antenna with four-element series slot-fed array for circular polarization diversity, utilizing 45\({}^{\circ}\) inclined slots and a straight microstrip line feeder. The realizable antenna footprint is 20 \(\times\) 27.7 mm\({}^{2}\). The measured results confirmed that the suggested design features a bandwidth of 3.8 GHz and a peak gain of 11.86 dBi. Metamaterials offer a powerful tool for optimizing the performance of MIMO systems. By carefully integrating these engineered materials, it is possible to achieve significant improvements in gain, isolation, and overall system efficiency. The proposed design, with its unique combination of features, demonstrates the potential of metamaterials in revolutionizing future wireless communication technologies. Research has explored various approaches to enhance isolation in dense antenna arrays. These include utilizing periodic metamaterial photonic bandgap structures for applications like MIMO and synthetic aperture radar (SAR) [22; 23; 24; 25; 26], investigating the impact of surface wave effects caused by metasurface in MIMO/SAR systems [26], and utilizing metamaterials as electromagnetic bandgap (EM-BG) layers to minimize mutual coupling and improve performance in challenging communication environments [27; 28; 29; 30; 31]. The proposed design presented here offers several key advantages:  
* It achieves a high peak gain of 13 dBi operating at 28.8 GHz that enhances signal directivity and extends the communication range. * It realizes a bandwidth of 1.0 GHz, around 28.8 GHz, measuring a reduced reflection coefficient of \(-\)27 dB, enabling the low loss operation. * It demonstrates isolation levels of 34.5 dB across its ports, effectively rejects interference and ensures strong, clear signal transmission. These results were experimentally validated to test the design's reliability, creating a promising candidate for future 5G mmWave. The organization of this paper is as follows: Section 2 discusses the methodologies and materials, Section 3 presents the results and discussion, and Section 4 provides the conclusions.