# Pentaband Dual-Polarized Antenna for Multiservice Wireless Applications
## 1 Introduction  
Wireless communication has become an integral part of modern society, and as the demand for wireless services continues to grow, industries are seeking ways to provide reliable and efficient wireless communication across multiple frequency bands [1; 2; 3; 4]. Multiband technology has emerged as a solution to this problem, as it allows for the use of multiple frequency bands simultaneously, thereby improving spectral efficiency, increasing channel capacity, and reducing multipathing. One type of antenna that is particularly useful for multiband operation is the printed patch antenna. Printed patch antennas are cost-effective, are easy to implement, and can communicate across multiple bands, making them an attractive option for wireless communication applications. However, to fully realize the benefits of multiband technology, it is essential to combine it with multiple-input-multiple-output (MIMO) systems [5]. MIMO technology enables high spectral efficiency, high data rates, and reliable communication between sending and receiving terminals. Compared to a single antenna, MIMO systems offer significant advantages, making them crucial components of modern wireless communication [6; 7; 8]. As the demand for wireless communication continues to grow, there has been a significant increase in the development of multiband MIMO antenna concepts for existing wireless systems in recent years [9; 10]. However, designing MIMO antennas presents a primary challenge of reducing the coupling between adjacent antenna elements [11]. Reducing the coupling between antenna elements is essential, as it directly impacts the system's throughput [12]. Therefore, various decoupling strategies have been explored in the literature, including using a slit on the ground plane, neutralization lines, parasitic structures, frequency-selective surfaces, and artificial metamaterials. For instance, some researchers have proposed using slots on the ground plane to achieve decoupling in dual-band MIMO antennas [13], while others have applied the neutralization technique to ultrawideband structures to reduce mutual coupling [14; 15]. However, these decoupling methods have limitations and may not be suitable for all applications. Other researchers have proposed more complex decoupling strategies, such as using parasitic structures, frequency-selective surfaces, and artificial metamaterials [16; 17; 18]. These designs are generally used for single narrow-band applications and utilize multilayer structures, making the design more complex. In previous studies, researchers have explored multiband MIMO antennas with dual ports [19; 20; 21; 22; 23] and quad/multiport ports [24; 25; 26; 27; 28; 29]. The dual-port antenna design proposed in [19] utilized a defective ground and parasitic element to create a dual-band antenna suitable for WLAN applications. In another study [20], stubs were integrated into the feedline and ground plane to achieve 20 dB isolation in tri-arm triple-band MIMO operation. In a third design [21], researchers proposed 3 iterations of a hexagonal aperture on a hexagonal patch for pentaband applications, which achieved over 21 dB isolation with a defective ground. More recently, a study focused on a planar log-periodic array that achieved 23.5 dB of element isolation without decoupling structures for Ku/K-band wireless communications [22]. This design utilized a log-periodic antenna element and a specific feed network to realize multiband MIMO performance without decoupling structures. Additionally, an E-shaped compact MIMO antenna was proposed for pentaband applications [23], although it achieved very low isolation. Compared to dual-port models, achieving high isolation in multi-port antennas becomes more challenging as the number of elements increases due to increased coupling effects. One approach to achieving high isolation among antenna elements is to incorporate circular and rectangular slots on a square-shaped patch, which was used to achieve 16 dB isolation below 6 GHz across the three operating bands of 5G [24].