## 1 Introduction  
The surging demand for data driven by the proliferation of electronic devices has placed significant pressure on current communication systems. This escalating demand necessitates higher data rates, demanding significant advancements in wireless technology and broadband integration. Each successive generation of wireless technology introduces new features and surpasses the performance of its predecessor. Fifth-generation (5G) wireless technology influenced a diverse spectrum of frequencies, each with distinct characteristics. Sub-1 GHz bands offer extensive coverage for outdoor users, and mid-band frequencies including 2.5, 3.5, 3.7-4.2, and 4.8-5 GHz offer a balance between coverage and data capacity. Conversely, millimeter-wave (mmWave) bands operating above 24 GHz promise exceptionally high data rates but currently suffer from limited coverage. The Federal Communications Commission (FCC) has designated certain frequency ranges for 5G deployment, such as the 24 GHz, 28 GHz, 37, 40, and 47 GHz bands for licensed operations [1, 2, 3, 4, 5]. Additionally, the 64 to 71 GHz spectrum has been reserved for unlicensed applications, enabling technologies such as Wi-Gig and various ultra-fast wireless communication systems [6, 7]. Multiple-input multiple-output (MIMO) antenna systems, which utilize multiple antennas at both the transmitting and receiving ends, substantially improve wireless communication performance in several key areas. By enabling the concurrent exchange of multiple data streams, MIMO technology boosts data rates, strengthens signal reliability, and elevates overall network efficiency. This has driven significant interest in advancing MIMO antenna designs, especially for operation in the mmWave frequency spectrum, making it a prominent and dynamic research focus in modern telecommunications [8; 9; 10]. Antennas designed for the 28 GHz band (N261, 27.5-28.35 GHz) must address the challenges of mmWave propagation, including high path loss, atmospheric attenuation, and the need for dense network deployments. A critical requirement is a wide bandwidth to cover the allocated spectrum, enabling support for high data rates and channel aggregation in 5G new radio (NR). High gain (10-15 dBi or higher) and directional beamforming capabilities are essential to compensate for signal attenuation and enable precise user tracking in dynamic environments. For MIMO configurations, antennas must achieve low mutual coupling (isolation > 30 dB) and ultra-low envelope correlation coefficients (ECC < 0.1) to ensure independent operation and maximize spatial multiplexing gains. Compact physical dimensions are equally vital as mmWave systems often require dense antenna arrays (e.g., 4 \(\times\) 4 or 8 \(\times\) 8 MIMO) integrated into small devices like smartphones or IoT modules. Critical requirements for successful MIMO antenna design in 5G involve achieving high spectral efficiency, minimizing interference, and dynamically adapting the bandwidth--key factors in advancing 5G capabilities. Meeting these demands relies on spectrum-efficient infrastructure, resilient interference mitigation strategies, and flexible bandwidth allocation to address shifting network requirements. MIMO technology has been widely acknowledged for its ability to enhance spectral efficiency via methods like spatial multiplexing and beamforming. These approaches leverage adaptive radiation patterns, polarization diversity, and directional signal transmission to suppress interference and optimize performance in dense communication environments [11; 12; 13; 14; 15]. MIMO antenna design faces several critical challenges, including minimizing interference between antenna elements (mutual coupling), reducing size and complexity, maximizing signal strength (gain), broadening the usable frequency range (bandwidth), and ensuring efficient operation. Previous research has explored various innovative antenna designs to overcome these challenges and advance MIMO technology.