# Compact Sub 6 GHz Slot Multiantenna System for 5G Laptops
## 5 Parametric Study
With increases in parameter \(t\), the impedance matching condition at the second resonant mode deteriorates and slightly shifts to high frequency. The ultimately optimized parameter \(t\) is 5.5 mm. As parameter \(d\) increases, the first resonant frequency significantly decreases, and the second resonant frequency shifts less. The final value of parameter \(d\) is 32 mm. As the parameter gap grows, the impedance matching condition for the first resonant mode improves and shifts toward higher frequencies. The ultimately optimized parameter gap is 1 mm. The parametric analysis of each design parameter is described below to understand the impact on the antenna characteristics. The comparison of the simulated reflection coefficient with a change in the capacitance value \(C\) is shown in Figure 13. It can be seen that when the capacitance value rose, there was a tendency for both low- and high-frequency modes to drop in frequency. This occurred  
Figure 12: Comparison of the simulated reflection coefficient of a T-shaped feed-in section with and without a chip capacitance \(C\). mainly because when the capacitance value grows, the virtual impedance increases, causing the frequency to drop through zero virtual impedance. The resonance frequency points can therefore be adjusted by changing the capacitance value to modify the virtual impedance of the low- and high-frequency modes. Regarding the changes in the length of the left and right branches in the T-shaped feed-in section, Figure 14 compares the reflection coefficients for the right-side branch parameter \(r\). The figure demonstrates that increasing the length of the right-side branch from 11 mm to 13 mm resulted in changes to the reflection coefficients. There was a clear tendency for both low- and high-frequency modes to decrease in frequency. This primarily occurred in the length where the right-side branch was situated in the distribution area of the strong electronic field when the low- and high-frequency modes were excited, and then the variations in length and the coupling levels had a marked effect on both low- and high-frequency modes. A comparison of the reflection coefficients for the left-side branch parameter \(t\) in the T-shaped feed-in section is provided in Figure 15, which indicates that when the left-side branch grew from 4.5 mm to 6.5 mm in length, there was a clear tendency for the high-frequency modes to fall in frequency. However, there was no significant change in the low-frequency modes. This was primarily in the length in which the left-side branch was situated in the distribution area of the strong/weak electronic fields when the high-/low-frequency modes were excited. The variations in length and the coupling levels thus had/did not have a marked effect on the high-/low-frequency modes. Figure 14: Comparison of simulated reflection coefficients with changes in parameter \(r\). Figure 13: Comparison of simulated reflection coefficients with changes in \(C\). Then, a parameter analysis of the length \(d\) of the slotted hole was conducted. A comparison of the reflection coefficients for parameter \(d\) is shown in Figure 16. We can clearly see from the diagram that when the slot length was reduced from 34 mm to 30 mm, there was upward trends in both the low- and high-frequency modes. This was followed by an analysis of the variation in the coupling gap between the T-shaped feed-in section and the slotted hole. A comparison of the reflection coefficients for the parameter gap is shown in Figure 17. When the gap width grew from 0.8 mm to 1.2 mm, the coupling level between the low and high frequencies fell, resulting in a boost in the low-frequency mode. The boost in the high frequencies was not significant, but the matching noticeably changed. Based on the analysis mentioned above, we could adapt the low- and high-frequency resonance frequencies and their matching by applying the capacitance value of the T-shaped feed-in section, the length of the left and right branches, and the coupling distance between them and the slotted holes.