# Uni-Planar MIMO Antenna for Sub-6 GHz 5G Mobile Phone Applications
## 2 Proposed Uni-Planar MIMO Antenna
### Fabrication and Measurements  
A fabricated prototype of the proposed MIMO antenna is illustrated in the inset of Figure 7 along with the feeding mechanism. A prototype was fabricated using an LPKF-D104 milling machine and evaluated with an Agilent Precision Network Analyzer (PNA-E8363C). A flexible, semi-rigid RF cable is used for the feeding purpose. One end of the cable is connected to the antenna, while the second end is connected to a coaxial connector. Due to the similar performance and placement of the antenna elements, only port-1 and port-2 are measured and compared.  
A comparison between simulated and measured S-parameters is depicted in Figure 7. A reasonable agreement is observed between simulated and measured \(S_{11}\) and \(S_{21}\). The simulated \(-6\) dB and \(-10\) dB impedance bandwidths are noted to be 1.38 GHz (2.98-4.36 GHz) and 620 MHz (3.2-3.82 GHz), respectively, while the measured bandwidths are 1.45 GHz (2.96-4.41 GHz) and 680 MHz (3.13-3.81 GHz), respectively. Besides this, the isolation between antenna elements is \(>\)10 dB (see Figure 7) at the desired frequency band.  
The simulated and measured ECC and TARC results are illustrated in Figure 8. It is observed that the simulated and measured data comply with each other. The ECC value for the band of interest is \(<\)0.08, as shown in Figure 8a. Aside from that, the TARC value for the operating band is 20 dB, as shown in Figure 8b.  
Figure 6: Simulated (**a**) ECC, (**b**) DG, and (**c**) TARC results of the proposed sub-6 GHz MIMO antenna.  
The simulated and measured realized gain for port-1 is shown in Figure 9a. The gain is measured by exciting port-1, while port-2 is terminated using a 50 \(\Omega\) matched load. The average simulated and measured realized gain at port-1 is noted to be 4 dBi (see Figure 9a). The simulated realized gain varies in the range from 2 to 4.75 dBi, while the measured realized gain fluctuates in the range of 2.14-4.59 dBi, as shown in Figure 9a. The radiation and total efficiency results for port-1 are shown in Figure 9b. It is observed that the designed antenna has a radiation efficiency \(>\)90%, while the total efficiency fluctuates in the range of 70-95%. One thing that needs to be observed from Figure 9b that the designed antenna offers constant radiation efficiency in the band of interest.  
The simulated and measured radiation characteristics for port-1 and port-2 for frequencies 3.2 GHz, 3.5 GHz, and 3.9 GHz are illustrated in Figures 10 and 11. The designed MIMO antenna provides quasi-omnidirectional radiation characteristics for both _yz_- and _xz_-plane at the given frequencies. In addition, the MIMO antenna offers pattern diversity in the _xz_-plane, as seen in Figures 10 and 11. Moreover, the measured results are well-matched with the simulated data for both planes.  
Figure 8: Simulated and measured (**a**) ECC and (**b**) TARC of adjacent antenna elements.  
Figure 7: S-parameters of adjacent antenna elements (inset of the figure shows fabricated sub-6 GHz MIMO antenna along with the feeding mechanism).  
Figure 10: Radiation characteristics of the proposed sub-6 GHz MIMO antenna when port-1 is excited.  
Figure 9: (**a**) Simulated and measured realized gain, and (**b**) radiation and total efficiency of the proposed sub-6 GHz MIMO antenna when port-1 is excited.