# Four-Port MIMO Antenna System for 5G n79 Band RF Devices
## 3 Results and Discussion
### Performance Parameters  
The performance parameters of the antenna are vital in analyzing antenna performance. This section includes the basic antenna performance characteristics as well as the MIMO characteristics. Figure 8 shows the antenna efficiency and maximum gain over frequency, from which we can observe that the total efficiency of the antenna varies between 68 and 72%, while the maximum gain at the desired resonance is 2.8 dBi. The simulated and measured results are in proximity. Figure 8: Antenna performance parameters. Figure 7: Surface currents at 4.8 GHz: (**a**) Ant 1, (**b**) Ant 2, (**c**) Ant 3, (**d**) Ant 4. Similarly, the MIMO antenna performance characteristics include the envelope correlation co-efficient (ECC) and the diversity gain in Figure 9. The ECC can be estimated with S-parameters or far fields, but here it is calculated with far-field patterns using Equation (1). \[ECC=\frac{\left|\iint 4\pi(\overrightarrow{B_{i}}(\theta,\varphi))\ x\ ( \overrightarrow{B_{i}}(\theta,\varphi))d\Omega\right|^{2}}{\iint 4\pi|(\left| \iint 4\pi(\overrightarrow{B_{i}}(\theta,\varphi))\right|^{2}d\Omega\iint 4\pi|( \overrightarrow{B_{i}}(\theta,\varphi))|^{2}d\Omega} \tag{1}\]  
where \(\overrightarrow{B}=(\theta,\Phi)\) denotes the 3D radiation pattern upon excitation of the \(i\)th antenna, and \(\overrightarrow{B}=(\theta,\Phi)\) denotes the 3D radiation pattern upon excitation of the \(j\)th antenna. \(\Omega\) is the solid angle. The ECC of the proposed antenna among any two radiating element is less than 0.07, which shows that our proposed antenna MIMO elements are well correlated, and also that the diversity gain lies in a satisfactory range. The diversity gain refers to improvements in the signal-to-interference ratio by applying any diversity scheme. Since the antenna shows a diversity gain with higher values, a better isolation is achieved. DG is calculated using Equation (2). Table 2 shows the proposed antenna compared with those from the published literature. \[DG=10\sqrt{1-\left(ECC\right)^{2}} \tag{2}\]  
Another important MIMO parameter calculated is channel capacity (cc). The channel capacity is calculated using different SNR values ranging from 14 to 26 with an interval of 3 dB in a Rayleigh fading environment. It has been found that, as the SNR level is increased, the channel capacity gets better, with an approximate value of 6 bps/Hz. Figure 10 shows the calculated CC at different SNRs. Figure 9: MIMO performance parameters. One of the important factors to consider while designing antennas for user experience is the safety concern. An SAR analysis is usually conducted for validating the safety levels for users. The energy absorbed (SAR) by the user tissues need not cross the value of 1.6 W/Kg for 1 g tissue and 2 W/Kg for 10 g tissue. The SAR analysis was conducted using the EM software tool HFSS and a head model was used for this purpose because, as the proposed design is intended for the use of 5G services, it can be accompanied in future smart phones. In Figure 11, the SAR results of 1 g tissue are given. The peak SAR value of 0.96 W/Kg was observed, which indicates that the proposed antenna system is completely safe for use.