# Designed Circularly Polarized Two-Port Microstrip MIMO Antenna for WLAN Applications
## 5 Results and Discussion of MIMO-CP  
The simulation results were generated using CST Microwave Studio software. The proposed MIMO-CP antennas fabricated are shown in Figure 10. In the following paragraphs, the simulated and experimental results of MIMO-CP are explained.  
The fabricated antenna, S-parameter, was tested by using a PNA performance network analyzer. Simulated and measured S-parameter results of the antenna are given in Figure 11. The simulated and measure results were almost matching, but some mismatches were observed, possibly due to the effect of the SMA connector. The simulated and measured results show good agreement within the frequency band. Figure 12 presents the simulated and measured AR results comparison. The AR of the proposed radiator is in the broadside direction; however, the proposed antenna measurement and simulation results of CP remain below 3 dB AR within the antenna bandwidth.  
Figure 8: (a) S-parameters of different plots for various distances (\(d\)). (b) Axial ratios of different plots for various distances (\(d\)).  
Figure 9: (a) Simulated S-parameter for the antennas with different widths of ground slot, \(c\). (b) Simulated axial ratio of different widths of ground slot, \(c\).  
Figure 13a shows the simulated and measured gains of the proposed MIMO-CP antenna. The antenna peak gain is obtained at 5.6 GHz around 6 dB, which is suitable for practical applications. Efficiency is also the important parameter of the antenna, as shown in Figure 13b. In the operating bandwidth, the simulated radiation efficiency of the proposed MIMO-CP antenna is greater than 80%. The efficiency of the experimental antenna is measured in an anechoic chamber. It can be seen that the measured and simulated S-parameters are in good agreement; however, there are some discrepancies among experimental and simulated S-parameters (this is due to manufacturing tolerances and variations in the characteristics of the material used).  
Figure 11: Simulated and measured S11/S21 of the antenna.  
Figure 10: Prototype of fabricated MIMO-CP antenna. (**a**) Front view. (**b**) (Back view). (**c**) Bottom view.  
The suggested simulated and measured antenna 2D far-field radiation patterns are shown in Figure 14, on two main planes--E-plane and H-plane, respectively--at a central frequency. The impact of the resonators on the antenna radiation patterns was investigated using simulation and measurement results for H-plane and E-plane far-field radiation patterns for the two fabricated MIMO-CP antennas. Figure 14 shows the radiation patterns that occur when port-1 is excited and port-2 is terminated by a matched load. Both the E-plane and H-plane radiation patterns are directional. The 2D left-hand CP (LHCP) and right-hand CP (RHCP) radiation patterns for port-1 at 5.6 GHz are shown in Figure 15. When port-1 is excited, the RHCP field component is stronger than the LHCP component in the broadside direction. The proposed antenna is right-handed circularly polarized, because the RHCP pattern is \"more than\"--as compared to LHCP--at both the E-field and H-field.  
Figure 12: Simulated and measured AR.  
Figure 13: (**a**) Simulated and measured gain of the proposed antenna. (**b**) Simulated and measured radiation efficiency of the proposed antenna.