## 4 Experimental Validation  
Four MIMO antennas based on the coaxial probe, microstrip line, proximity coupled, and aperture coupled feed methods have been manufactured using the conventional photo-lithography technique in order to verify the simulation results. Photographs of the fabricated MIMO antenna designs are shown in Figure 33a. The anechoic chamber at Barkhausen Institut in Germany was used for the fabricated MIMO antenna measurements. Their transmission and reflection characteristics were measured using a Keysight N5224B PNA microwave network analyzer. A standard horn antenna was used to measure the gain patterns. While measuring the radiation parameters of the MIMO antennas, a 50 \(\Omega\) termination resistance was used. Two different antenna inclinations were used for radiation pattern measurements: vertical and horizontal in the port direction. A photograph of the proposed antennas under measurement in the anechoic chamber is demonstrated in Figure 33b. A substantial portion of the sets of observations showed good agreement between the measured and simulated results for the fabricated MIMO antennas. Similar  
Figure 31: CCL of MIMO antennas with SCSRR-based DGS for each feeding methods.  
Figure 32: MEG of MIMO antennas with SCSRR-based DGS for each feeding methods.  
effects were observed when one port of the fabricated MIMO antenna was stimulated whereas the remaining port was 50 \(\Omega\) terminated. However, simulation to measurement differences have been noticed in the isolation results. The primary causes of the discrepancy include undesirable electromagnetic radiation through the feed cable, incorrect alignment, connector or 50 \(\Omega\) termination resistance tolerances, and errors in the production phase.  
The MIMO antennas showed measured BW and isolation values of 150 MHz and 46 dB for coaxial feed, 125 MHz and 22 dB for microstrip line feed, 312 MHz and 38 dB for proximity coupled feed, and 312 MHz and 17 dB for aperture coupled feed, as shown in Figures 34, 35, 36 and 37, respectively. The discrepancies in the simulated and measured isolation are attributable to the electromagnetic radiations from the feed cable. Note that the measured peak isolation values is concerned only in \(-\)10 dB matching area and then too, the number for coaxial probe feed antenna was relatively better. As it is seen from the comparison, there is are different frequency shifts between \(S\_1\_1\) parameters for measurement and simulation. That could occur because of the calibration of equipment, soldering of feed mechanism (which directly affects impedance matching) as well as different surface roughness of the antennas.  
Figure 33: Photographs of the fabricated MIMO antennas with SCSRR-based DGS for (**a**) different feed networks and (**b**) aperture-coupled feed.  
The simulated and measured radiation patterns of the MIMO antennas with coaxial probe, microstrip line, proximity-coupled, and aperture-coupled feed methods at 5.8 GHz are displayed in Figures 38, 39, 40, and 41, respectively. Nearly omnidirectional patterns was noticed. In the operational frequency band of every MIMO antenna, the realized gain was \(\approx\)5 dBi.  
Figure 34: Simulated and measured S-parameters of coaxial feed MIMO antenna with SCSRR-based DGS.  
Figure 35: Simulated and measured S-parameters of microstrip line feed MIMO antenna with SCSRR-based DGS.  
Figure 36: Simulated and measured S-parameters of proximity coupled feed MIMO antenna with SCSRR-based DGS.  
Figure 39: Simulated and measured radiation patterns of microstrip line feed MIMO antenna with SCSRR-based DGS: (**a**) E-plane; (**b**) H-plane.  
Figure 37: Simulated and measured S-parameters of aperture coupled feed MIMO antenna with SCSRR-based DGS.  
Figure 38: Simulated and measured radiation patterns of coaxial feed MIMO antenna with SCSRR-based DGS: (**a**) E-plane; (**b**) H-plane.