# Compact Sub 6 GHz Slot Multiantenna System for 5G Laptops
## 5 Parametric Study  
To verify the operating principle of the antennas and to provide a clearer picture of the contribution path of each mode in different frequency bands, we analyzed the electronic field distribution of the antennas at the two resonant frequency points, 3450 MHz and 4900 MHz, in the low- and high-frequency bands. The simulated electronic field distribution of the single antenna at 3450 MHz and 4900 MHz is demonstrated in Figure 11. It is evident from the figure that at 3450 MHz operation, the electronic field distribution followed the one-half wavelength resonance of a closed slot, with the maximum field occurring at the center of the slot. At 4900 MHz operation, the electronic field distribution followed the full wavelength resonance of a closed slot, with two peak fields occurring on both sides of the slot. It is notable that the distribution of the two peak fields on both sides is slightly asymmetrical because of the T-shaped feed-in section with a long coupling interval adjacent to the left side. In Figure 12, the simulated reflection coefficients of the proposed single-antenna T-shaped feed-in section with and without a chip capacitor are compared. The figure shows that the closed-slot antenna, featuring a basic T-shaped feed-in section, displayed a resonance mode at 4200 MHz. Notably, the real impedance of the antenna in the low-frequency band ranged between 25 and 125 ohms. However, its virtual impedance was too high to achieve a match. By adding a chip capacitor to the T-shaped feed-in section, the extremely high  
Figure 11: Electronic field simulation and distribution for single antennas at 3450 MHz and 4900 MHz. Figure 10: Calculated ergodic channel capacities of 5G antenna array prototype in 6 \(\times\) 6 MIMO system. virtual impedance at low frequencies could be reduced to achieve a match, resulting in a resonance mode at 3450 MHz. At this point, the resonance mode at 4200 MHz also dropped as a result of the virtual impedance, shifting the resonance frequency to 4900 MHz in the sub 6 GHz high-frequency band and allowing the proposed single antenna to cover both the 3300-3600 MHz and 4800-5000 MHz dual-band operations required for sub 6 GHz antennas. The design of the single antenna is characterized by the use of a long T-shaped metal wire segment for coupling and exciting the closed-slot configuration, which allows it to provide resonance modes at high frequencies. At low frequencies, the amount of coupling is too much for the virtual impedance that is too high to yield resonance modes. As a result, a suitable capacitance element was incorporated in the feed-in section for lowering the initially higher virtual impedance at low frequencies to achieve a match and generate a low-frequency resonance mode, and the original high-frequency mode was also boosted to 4900 MHz. As such, the asymmetric T-shaped feed-in section with a chip capacitor could effectively excite one-half and full wavelength resonance modes of the closed slot structure to encompass the 3300-3600 MHz and 4800-5000 MHz dual-band operations required for sub 6 GHz antennas. In order to further understand the design parameters of the unit element slotted dual-band antennas, we analyzed five design parameters that affect the characteristics of antennas. The five design parameters included capacitance value \(C\), the length \(d\) of the slotted hole, the coupling gap between the T-shaped feed-in monopole and the slotted hole, the length \(r^{\prime}\) of the right branch, and the length \(t^{\prime}\) of the right branch in the T-shaped feed-in monopole. The variation in parameter \(C\) affects both resonant modes. With the increase in \(C\), two resonant points move to low frequency due to the virtual impedance transform. The optimized value of parameter \(C\) is 0.5 pF. A little resonant frequency offset of the first resonant mode arises with the increase in parameter \(r\), and the major impact is caused for the second resonant mode. The final value of parameter \(r\) is 12 mm.