## 1 Introduction  
The radio access network (RAN) contributes significant capital expenditure (CAPEX) in any cellular network, and for 5G RAN, the cost increases from 45% to 65% [1, 2]. Historically, this part of the network was vendor-dependent [3, 4, 5]. For any mobile network operator (MNO), the core of the network can be virtualized entirely, but as far as the RAN is concerned, it evolved through multiple stages: from distributed RAN, where the base band unit (BBU) and the radio resource unit (RRU) are colocated, to a centralized RAN, where the BBU and RRU are decoupled, and to a virtualized RAN, where the BBU or its functional parts are virtualized. These virtualized parts are deployed on a commercial off-the-shelf (COTS) server in the form of a software package [6]. And most recently, the ORAN has emerged, which not only increases virtualization but also breaks the vendor dependency by introducing open interfaces. Multiple split options are available for various applications, which increase the ORAN flexibility and adaptability [7]. The development of a promising MIMO antenna for the ORAN has become a top priority among researchers and the industrial community as it is a crucial part of the RF components needed for the 3 GPP split option of a RAN [8]. MIMO technology is indeed widely used in various wireless communication systems, including wireless local area networks, as well as in public and private cellular networks. According to 3 GPP Release 18, in Technical Specification 38.104, a single 5G MNO requires a 100 MHz band for uplink or downlink communication. From the perspective of a neutral host organization, 300 MHz is required to support three different MNOs [9]. Further shared infrastructure also provides flexibility in resource management. Designing MIMO antennas involves addressing port isolation and gain enhancement while meeting requirements for bandwidth, cost, and size requirements. Researchers have explored various methods to reduce mutual coupling, including defected ground structures (DGSs) [10], which enhance isolation, and parasitic elements between radiating elements that act as absorbers [11]. Additionally, neutralization lines [12] and electromagnetic band gap (EBG) structures [13] have been used to suppress surface wave propagation and minimize interelement coupling in MIMO systems. These techniques have significantly improved the key performance parameters of MIMO antenna arrays. Recent studies have further advanced MIMO antenna design by integrating innovative structural and spatial techniques. For instance, ref. [14] proposed an eight-port MIMO antenna comprising two equal modules. Each module consists of four coaxial probe feed patches with a shared radiator. Elements are separated by an additional central patch with ground shortening pins and four I-shaped slots. The arrangement of elements increases the operational bandwidth by exciting multiple characteristic modes of CMA, but port isolation and gain remain less than 12.5 dB and 2.5 dB, respectively. In another approach, [15] utilizes a frequency selective surface (FSS) positioned above four radiating elements to achieve a peak gain of 4.8 dB. Although the designed scheme achieves a wider bandwidth from 3.8 to 6 GHz, the isolation between elements remains at 20 dB even with the use of a low dielectric loss substrate. Similarly, the eight-port MIMO antenna presented in [16] utilizes E-shaped and I-shaped slots to achieve a broader bandwidth from 3.3 to 6 GHz. However, the designed antenna achieves 20 dB isolation even after introducing a single-ended spanner-shaped slot between radiating elements. The twin-element MIMO antenna proposed in [17] consists of a T-shaped hemispherical feeding patch, left-arm and right-arm radiating patches, and a conjoined triangular ground plane, which achieves a wider band (3.4-6 GHz) and isotropic gain up to 4.5 dBi. But the mutual coupling reached \(-\)15 dB.