# Compact Sub 6 GHz Slot Multiantenna System for 5G Laptops
## 2 Proposed MIMO Antenna System Design  
The overall design of the dual-band 5G MIMO six-antenna system proposed in this paper is shown in Figure 1. The design is based on a screen ground plane and a keyboard ground plane with the dimensions of 300 \(\times\) 200 mm\({}^{2}\), which is approximated to the dimensions of a 13\" laptop in the market today. Copper sheets were used to make the screen and keyboard ground planes. There was a clearance space of 217 \(\times\) 3 mm\({}^{2}\) at the position 1 mm from the upper edge and 40 mm from the left edge of the screen ground plane, which was intended for the installation of a 5G MIMO six-antenna system. The dimensions of the clearance space are the same as the ones of the six-antenna system. The dual-band 5G MIMO multiantenna system (including Ant 1, Ant 2, Ant 3, Ant 4, Ant 5, and Ant 6) was composed of six identically structured and sized closed-slot antennas configured 5 mm apart from each other, side by side, in the same direction. The dimensions of each antenna was 32 \(\times\) 3 mm\({}^{2}\). The six antennas were printed on a substrate made of FR4 glass fiber with a thickness of 0.4 mm. The dimensions of the substrate were 221 mm \(\times\) 5 mm with a relative dielectric constant of 4.4 and a loss tangent of 0.02. The ground pads were printed around the FR4 glass fiber substrate and were connected to the screen ground plane. A ground pad was 2 mm long and 1 mm wide at the top and bottom. To maximize space utilization in laptops and enhance the operational bandwidth of antennas, a 300 \(\times\) 3 mm\({}^{2}\) copper sheet was vertically attached to the upper edge of the screen ground plane. This increased the bandwidth of the antennas, allowing each one to support sub 6 GHz dual-band operations at 3300-3600 MHz and 4800-5000 MHz.  
Figure 2 depicts the detailed design for one of the 5G antennas. As the 5G six antennas were the same structure and size, Ant 1 is taken here as the example for the illustration of the structure of a single antenna. With a 32 \(\times\) 3 mm\({}^{2}\) rectangular closed-slot, a single antenna was coupled with an asymmetric T-shaped feed-in section with a 0.5 pF chip capacitor for exciting the one-half and full wavelength resonance modes of the closed slot to cover the sub 6 GHz dual-band operations at 3300-3600 MHz and 4800-5000 MHz. Chip capacitors were used here to improve the impedance matching in the low- and high-frequency bands to effectively trigger the low-frequency modes and to adjust the resonant frequencies of the high-frequency modes. In addition, T-shaped asymmetrical left and right branches were employed for adjusting the coupling levels at low and high frequencies. The signal feed-in point in the figure is denoted as point A, and it was connected to the inner conductor of a mini coaxial line with a characteristic impedance of 50 ohms. The outer conductor of the mini coaxial line was connected to point G, which was a ground short-circuit point on the metal ground plane of the screen.  
The six-antenna system was designed with the concept of a closed-slot configuration, which could effectively excite the one-half wavelength and full wavelength resonance modes of the closed-slot structure at both low and high frequencies. When exciting the low- and high-frequency modes, the strength of the electric fields at the left and right ends of the slot decreased. As a result, the likelihood of coupling excitation affecting the neighboring slot antennas was reduced, resulting in a closed-slot antenna that can be closely integrated into a multiantenna system with excellent isolation and ECC performance.