# Advanced Metamaterial-Integrated Dipole Array Antenna for Enhanced Gain in 5G Millimeter-Wave Bands
## 1 Introduction  
In recent years, there has been a noticeable increase in research and development in the high-frequency domain, specifically the millimeter-wave (mmWave) frequency band [1, 2, 3]. This surge is a part of a continuous pursuit to surpass the limitations of data transmission speed and network capacity, with a particular focus on the development of the next-generation mobile communication system, 5G. 5G promises not only superior speed compared to existing 4G LTE (Long-Term Evolution) systems but also lower latency and higher data rates over a wider frequency range [4, 5]. 5G technology is designed to support various data-intensive applications such as autonomous vehicles, artificial intelligence, and the Internet of Things (IoT), all of which require high-speed internet connections [6]. The recent and upcoming 5G millimeter-wave applications are demonstrated in Figure 1.  
One of the core technologies of the 5G network is New Radio (NR) technology, which utilizes the millimeter-wave frequency band ranging from 24 GHz to 86 GHz [7]. This frequency band, largely unused by previous generations of mobile communication systems, offers a very wide bandwidth that theoretically enables gigabit-level ultra-high-speed data transmission [8, 9, 10]. The use of such a wide bandwidth solves potential capacity issues faced by future wireless communications, providing a foundation for uninterrupted connectivity and ultra-fast data services to users [11]. Many countries have already considered or chosen the 26/28 GHz band for the construction of 5G networks, playing a crucial role in accelerating the global standardization and commercialization of 5G services [12, 13]. However, utilizing the millimeter-wave band comes with several challenges. Notably, the mm wave frequency band experiences relatively high propagation losses due to physical limitations such as attenuation by atmospheric molecules. To overcome these issues, communication systems require technical solutions such as high-gain antennas [14; 15; 16]. Recently, innovative antenna design methods have been proposed to enhance the performance of the millimeter-wave antenna [17; 18; 19; 20; 21; 22; 23; 24; 25; 26; 27; 28]. A quasi-Yagi array antenna with a folded dipole driver is proposed for 5G mm wave applications in [17], while a series-fed antenna array is proposed in [18] for high antenna gain. However, the antennas in both [17] and [18] suffer from narrow operating bandwidths. In [19], a partially reflective surface (PRS) is utilized with a Fabry-Perot cavity antenna to achieve high gain operating at the 60 GHz band, but this antenna occupies a larger space because of its double substrate layers with additional foam layers in between the substrate layers. Additionally, a log-periodic dipole array with director cells [20], planar segmented techniques [21], metasurface layers [22], slot antennas with substrate-integrated waveguides [23], defected ground antennas with metallic via [24], and clover-type antenna array techniques are utilized in the literature to enhance the performance the of millimeter-wave antennas [25]. However, these antennas either suffer from a large overall antenna volume [21; 22; 23] or very low antenna gain [24; 25; 26]. Besides the above-mentioned techniques, metamaterial is also becoming popular among researchers to enhance the performance of millimeter-wave antennas [27; 28; 29] because of its capability to enhance the gain and bandwidth of antennas. In [27], a metamaterial layer is utilized 16 mm above the designed patch antenna to increase the antenna gain. Likewise, in [28; 29], metamaterial is used to achieve high antenna gain. These reported works [27; 28; 29] achieve high antenna gain; however, all of these works have the limitation of a narrow bandwidth. Additionally, the antenna in [27] suffers from a large antenna volume. In this work, a high-gain millimeter-wave antenna is proposed based on metamaterial.