# A Dual-Polarized and Broadband Multiple-Antenna System for 5G Cellular Communications
## 1 Introduction  
The continuous evolution of wireless systems has driven demand for higher data rates and improved services. As a result, 5G wireless communication has emerged to tackle the challenges posed by the limitations of the current generation's (4G) cellular networks [1, 2]. It is poised that 5G technology can transform wireless connectivity by delivering a wide array of services, including enabling the IoT, enhancing mobile broadband, and offering ultra-reliable communication systems. Its ability to integrate these capabilities positions 5G a critical enabler for the next generation of connected devices and services [3]. One of the key technologies driving the advancements in 5G networks is MIMO systems. MIMO technology utilizes multiple antennas at both the transmitting and receiving ends, enhancing communication reliability and significantly increasing channel capacity. Byleveraging multiple signal paths, MIMO improves data throughput and efficiency in wireless communication systems, making it a key component in modern wireless networks. While MIMO technology has been extensively utilized in 4G LTE systems, it plays an even more pivotal role in 5G and 6G networks. By increasing the number of radiation elements, MIMO systems in 5G can achieve even higher performance levels. This makes it a highly efficient and promising solution for meeting the increasing demands of data-heavy applications [4]. In addition to its reliability and capacity benefits, MIMO technology also employs diversity schemes in antenna configurations. This involves sending the same signals with uncorrelated antennas, which helps combat fading and significantly improves the reliability of wireless links. By leveraging the benefits of MIMO technology and diversity schemes, 5G networks are poised to deliver seamless connectivity and cater to a wide array of emerging applications. Multiple antennas in the system enable advanced techniques like MIMO, beamforming, and spatial diversity, paving the way for efficient data transmission, improved link reliability, and overall performance enhancements in 5G smartphones [5; 6]. The focus on broadband capabilities is another key attribute enabling seamless connectivity across a wide frequency range [7]. In addition, by incorporating dual polarization, this antenna system allows the simultaneous transmission and reception of signals with both horizontal and vertical polarizations, significantly enhancing data throughput and mitigating potential interference issues. This capability is especially crucial in dense urban environments and areas with high network congestion, ensuring a stable and reliable connection for smartphone users [8]. As a result, 5G smartphones equipped with this technology can efficiently adapt to diverse network deployments, regulatory environments, and varying user requirements, ensuring a consistent and high-quality user experience. Moreover, printed antennas are becoming increasingly popular in cellular communications. Their compact size and simple design contribute to efficiency and ease of integration into mobile devices. Among various printed antennas, omnidirectional antennas such as monopole, slot, loop, and PIFA are predominantly employed in MIMO smartphone systems, as they offer superior omnidirectional coverage and wider bandwidth. These characteristics ensure comprehensive performance across different sides of the mainboard. In contrast, directional antennas like patch antennas are less commonly used due to their larger size and limited radiation coverage [9]. In recent years, various smartphone MIMO antenna designs have been reported to cater to the needs of sub-6 GHz cellular networks [10; 11; 12; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30; 31; 32; 33; 34; 35]. However, many existing smartphone antennas face challenges, such as narrow operational bandwidths, single-polarized radiators, or uniplanar designs that occupy substantial PCB space and increase system complexity.