# Compact Sub 6 GHz Slot Multiantenna System for 5G Laptops
## 1 Introduction  
In recent years, consumers have shown a preference for mobile communication products that offer high transmission rates, portability, lightweight, and large screen displays. Manufacturers have introduced a range of slim laptops with high screen-to-body ratios to meet these demands. However, the limited space in these devices has resulted in less space for antennas. As a result, the characteristics of many antennas installed in mobile communications devices are evolving into smaller sizes and lower profiles. Several multiple input, multiple output (MIMO) multiantenna systems for mobile devices and 5G applications [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28] have been continuously proposed with the rapid spread of 5G MIMO technology, which also include the 5G MIMO multiantenna systems for mobile phones. In these systems, multiple antennas are configured at appropriate distances to maintain a certain degree of isolation. The spacing between the antennas in them is about 10-30 mm [2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13]. Some designs incorporate isolation elements to optimize the degree of isolation between antennas [14, 15]. However, they occupy more of the limited space available in devices. A certain distance between two antennas is necessary for achieving a good degree of isolation. There are several multiantenna systems configured in close distances, in which the degree of isolation between antennas is optimized with the application ofa decoupling mechanism. For example, there are designs in which the branch points of two antennas are configured close to each other [16; 17; 18], designs in which a chip inductor is added to the end of two antennas' branches [19; 20], designs in which a chip capacitor is added to the common shorted branch of two antennas to form a band-pass resonant structure for the optimization the degree of isolation [21], and designs in which a band-pass resonant structure consisting of distributed capacitors and inductors is added to the shorted branch of two antennas to achieve decoupling [22]. A novel mushroom-inspired dual-band electronic bandgap structure was proposed to improve the isolation between closely packed antenna elements [23]. The ground part is located at the substrate's bottom to enhance the isolation performance of the MIMO antenna that was designed [24]. The authors employed a decoupling inductor and stop-band filter to reduce the mutual coupling and antenna size [25]. This is the first instance where a decoupling inductor was shared by two bands. To reduce mutual coupling, two decoupling branches (DBs) were implemented [26]. The implementation of the DBs effectively reduces mutual coupling at 3.5 GHz, while having minimal impact on mutual coupling at 4.9 GHz. In [27], a single antenna consisted of an H-shaped radiating element fed to the main board of the smartphone. Each side edge consisted of four radiating elements, and the gap between each antenna element was optimized to achieve low mutual coupling. In addition, there is a two-antenna design with two different excitation mechanisms that is able to achieve good isolation without the need for a distance between the two antennas. The profile height of the two-antenna element is 4 mm, and its length is 30 mm. It can cover the 5G 3400-3800 MHz band [28]. The MIMO antenna systems use slot structures [6; 7; 8; 9; 10; 11; 12; 13], which can be seamlessly integrated with metallic surroundings and are particularly suitable for devices with metal frames or back covers. Notably, refs. [10; 11; 12; 13] belong to the state-of-the-art literature within the past year. In [10], the authors proposed eight identical small inverted F-shaped folded slots etched onto a metal frame as a highly isolated MIMO antenna. Effective mitigation of the coupling between antenna elements can be achieved through the ideal arrangement of the positions of eight antenna elements. In [11], the authors proposed an eight-element antenna system that operates at sub 6 GHz.