Design of a Modified MIMO Antenna Based on Tweaked Spherical Fractal Geometry for 5G New Radio (NR) Band N258 (24.25-27.25 GHz) Applications  
[PERSON]  
1 Department of Electronics and Communication Engineering, Lovely Professional University,  
(27.5-28.35 GHz), which are specifically designated for millimeter wave (mm wave) 5G applications [3; 4].The 5G wireless technology system comprises two primary components, namely the core network and the radio access network. The core network is responsible for the handling of data and Internet connections in 5G wireless technology, while the radio access networks, comprising 5G small cells and macro cells, play a crucial role in the functioning of 5G wireless technology. Additionally, these networks facilitate the connection between mobile devices and the core network. The clustering of 5G small cells is necessitated by the limited propagation range of millimeter wave (mm-wave). The smaller cells serve as a complement to the macro cells, which are utilized to provide coverage over larger geographic areas [5].To broadcast and receive enormous amounts of data concurrently, macro cells use MIMO antennas with numerous connections. As a result, multiple individuals can connect to the network simultaneously. For the proper functioning of a multiple input multiple output (MIMO) antenna system, certain conditions must be met, including isolation between the antenna elements, diversity gain, envelope correlation coefficient, and mean effective gain [6; 7]. Nearly every single one of the designs for MIMO antennas that have been published in the relevant body of scholarly research only barely meets the minimum criteria of mutual coupling, which is very close to being an acceptable value. Some of the techniques that can be used for the purpose of enhancing the MIMO performance characteristics are as follows. The utilization of Characteristics Mode Analysis (CMA) has been proposed as a means to enhance bandwidth [8; 9; 10].The addition of rectangular-shaped slits and slots on both the patch surface and bottom plane, in conjunction with the utilization of orthogonal polarization, leads to a substantial decrease in mutual coupling [11]. The implementation of open-ended resonator slots on the patch, T-shaped stubs on the bottom plane, and L-shaped slits on the feedline has been found to enhance isolation, as reported in reference [12]. The patch's I-shaped slot and the flawed ground structure increase the bandwidth and reduce mutual coupling [13]. The design incorporates a rectangle slot, two vertical slots on the bottom plane, and a square slot on the surface of patch. In addition, a microstrip feed line with a tapered profile is utilized to enhance bandwidth and isolation, as mentioned in references [14; 15]. The combination of elliptical slots on the patch and a T-shaped stub on the bottom plane can significantly enhance the bandwidth and increase isolation, as stated in reference [16]. High isolation is provided by rectangular and triangular stubs on the patch, flawed ground structure, and orthogonal polarization [17]. DGS and dielectric layers increase the bandwidth and isolation [18]. A monopole antenna is composed of a half-disk-shaped radiator and a rectangular ground with a tapered microstrip feedline that increases bandwidth and minimizes the interaction between adjacent antennas [19]. The implementation of an L-shaped monopole and annular rings on the patch, along with a rectangular shaped slot on the bottom plane, and the utilization of orthogonal polarization, have been found to effectively mitigate mutual coupling, as reported in reference [20]. The use of the capacitively coupled approach has been employed to enhance isolation, as indicated by reference [21]. A cylindrical dielectric resonator with a two-layer substrate structure is utilized in order to enhance envelope correlation and gain, as stated in reference [22].