## 1 Introduction  
Future generation frequency for the upper mid-band has turned out to be a major building block of 5G due to its many benefits against mmWave technology. These include reversed coverage--especially in rural areas--lowered power consumption, better penetration, better data rates, and improved mobility [1, 2]. For expanding the demand of high-data-rate communication system, multiple antenna techniques at both the transmitter and receiver have developed. A glance at some of these systems like multiple-input multiple-output (MIMO) shows that they increase the channel capacity of communication links without necessarily increasing the allocated power or bandwidth [3, 4]. MIMO technologies are still one of the key elements of 5G wireless networks. Their performance is dependent on the multi-path characteristics of the communication channels and using carefully designed MIMO systems. On this front, low-profile wideband antennas are becoming popular due to their small size, light weight, lowered cost, and simpler fabrication. It additionally states that in the case of close placement of the antennas, there is great mutual coupling, which is undesirable from an efficiency aspect. For successful wireless communication in MIMO systems, a minimum isolation of 12 dB between antenna elements is required [5]. Several solutions have been put forward to tackle coupling and attain a high level of isolation. Some of these are parasitic elements [6], defected ground structures (DGSs) [7], stubs [8], self-isolating decoupling structures [9], and artificial intelligent techniques [10]. These methods are useful in the improvement of the performance of antennas, especially where the available space is very limited. Advancement of the fifth generation (5G) network is focused mainly on attaining the right amount of so-called spectral efficiency, bandwidth, and channel capacity, with the C-band (4.0-8.0 GHz) being the important frequency band of international interest [11]. MIMO antenna technology plays a vital role in 5G smartphones, helping to achieve faster data speeds, better signal reliability, and more efficient use of the available spectrum. Since smartphones have limited space, engineers have developed innovative antenna designs like planar inverted-F antennas (PIFAs), slot antennas, monopole arrays, dielectric resonator antennas (DRAs), and metasurface-based antennas to optimize performance while keeping interference low [12]. To further enhance signal quality, techniques such as decoupling networks, electromagnetic bandgap (EBG) structures, and metamaterials are used to reduce unwanted interactions between antennas. Another key challenge is specific absorption rate (SAR) compliance, ensuring that radiation exposure remains within safe limits. Solutions like artificial magnetic conductors (AMCs) and metasurfaces help balance safety with high performance [13; 14]. Thus, this band is an ideal solution for the economy and widespread distribution of coverage with 5G networks. In view of this, a large number of antennas is important in delivering high data rates [15]. But as wireless evolution advances to higher frequencies, this results in limitations such as short transmission ranges and more signal path loss. To counter these problems, solutions have been proposed such as the reconfigurable intelligent surface [16], which can actively manage the paths of signals within given systems. Further, the design requirements of wideband MIMO antennas for compact platforms such as smartphones face extra difficulties such as poor isolation between antennas and low space for integrating a number of antennas, which result in reduced spectral efficiency [17]. To avoid these challenges, the desirable antennas have a wider bandwidth, can operate in multiple bands, and have higher levels of separation between the elements. Nevertheless, the task of attaining improved spectral efficiency for 5G devices presents some real challenges.