# Compact Sub 6 GHz Slot Multiantenna System for 5G Laptops
## 3 Experiment and Measurement Results  
The overall design of the 5G MIMO six-antenna system is shown in Figure 3, and the details of the 5G MIMO six-antenna system and the single antenna are shown in Figure 4. Their measured dimensions are shown in Figures 1 and 2. A simulation study using a commercially available tool, High Frequency Structure Simulator (HFSS), was conducted [30]. The reflection coefficients were set to below \(-6\) dB (i.e., VSWR = 3:1). Based on the widely used design guidelines for mobile antennas, the transmission coefficients between these antennas were set to below \(-10\) dB [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]. As antenna elements 2343 the same with only a slight difference in the configuration position for the six 5G MIMO antennas, the impedance matching was roughly the same. To keep the diagram from being complicated with many curves, only simulated S\({}_{11}\) and measured S\({}_{11}\) were chosen as the representative reflection coefficients in Figure 5. We can see that the unit element was able to generate two resonance modes to encompass the sub 6 GHz dual-band operations of 3300-3600 MHz and 4800-5000 MHz. The simulated and measured data were in good agreement, and the reflection coefficients observed were all above \(-6\) dB in both the simulation and measurement. We noticed that the mismatch in the values of the reflection coefficients in both bands was mainly due to the presence or absence of the coaxial line. The coaxial line was not added in the simulation, but a 70 mm one was used as the feed in the implementation. The loss of the coaxial line caused slight differences in the simulated and measured reflection coefficients. Figure 1: Overall design of the six 5G MIMO antennas. Figure 2: Detailed structure of a single 5G antenna (Ant 1). S\({}_{12}\) is sufficient to explain the isolation when antenna elements are symmetric. In the same way, only simulated S\({}_{12}\) and measured S\({}_{12}\) were chosen as the representative  
Figure 4: Single closed-slot antenna detail structure. Figure 5: Simulated and measured reflection coefficients for Ant 1. Figure 3: Overall configuration of the 5G MIMO six-antenna system. transmission coefficients for Figure 6. This was primarily in consideration of the fact that the transmission coefficients between the two adjacent antennas would be higher than those among the antennas with more space in between [6]. It is clearly indicated in the figure that the simulated transmission coefficient of the unit element in the sub 6 GHz bands of 3300-3600 MHz and 4800-5000 MHz was not more than \(-9\) dB. However, the measured transmission coefficient was higher than \(-10\) dB. The distance between the adjacent antennas among the six antennas was only 5 mm, and the degree of isolation was still better than 10 dB, which is excellent performance compared with that of other devices with multiple antennas [6; 7; 16]. The efficiency of the antennas should be more than 40% for application in practical scenarios [6]. In addition to the degree of isolation between the antennas, the ECC serves as an essential reference parameter for MIMO antenna systems. Generally, an ECC of below 0.5 meets the criterion for practical applications [31]. The ECCs calculated from the simulated and measured complex electronic field radiation patterns for the dual-band 5G MIMO six-antenna system are shown in Figure 7, where the ECCs are all below 0.2 in the bands. This confirms the good channel independence among the antennas of this 5G MIMO six-antenna system. The simulations and measurements presented above exhibited several discrepancies, which could be attributed to the absence of transmission lines in the simulations. It might also have been caused by the parameters of either soldered or FR4 substrates or copper sheets, which might be slightly different from the simulations in practical application cases.