## 3 Results and Discussion  
To ensure the credibility of the acquired outcomes, an antenna is fabricated on a substrate composed of FR4 material. The frontal and lateral perspectives of the constructed antenna are illustrated in Figures 13a and 13b, respectively.  
The fabrication procedure is carried out using the EP-42 Auto PCB prototype machine. Connectors are used to attach the designed antenna to the ZNB- 40 VNA in order to determine its transmission and reflection coefficients. The measured results snapshot taken from VNA is displayed in Figure 14a. The suggested antenna's radiation pattern is measured in an anechoic room utilizing a reference horn antenna as the transmitter, as seen in Figure 14b.  
Figure 15a,b display the reflection and transmission coefficients, both measured and simulated. The antenna under consideration exhibits resonances at frequencies of 9.5 GHz, 11.1 GHz, 13.4 GHz, 15.8 GHz, 21.1 GHz, and 26.6 GHz, accompanied by corresponding S11 (dB) of \(-\)32.15, \(-\)11.95, \(-\)13.3, \(-\)17.0, \(-\)33.2, and \(-\)26.14, respectively. These resonances cover the frequency bands of 8.9-9.9 GHz, 10.4-11.4 GHz, 13.1-13.7 GHz, 15.4-16.2 GHz, and 17.7-28 GHz. Furthermore, the antenna demonstrates enhanced impedance bandwidths of 1000 MHz, 1000 MHz, 600 MHz, 800 MHz, and 10,300 MHz, respectively, within these frequency ranges. The maximum isolation between the two antennas is \(-\)48.37 dB. In the case of simulated findings, the antenna exhibits resonance at 9.7, 16.3, 18.8, and 21.4 GHz, accompanied by reflection coefficients of \(-\)20.04 dB, \(-\)12 dB, \(-\)31.9 dB, and \(-\)32.3 dB, respectively. The frequency ranges for the covering bands in the simulation are as follows: 8.2-10.4 GHz, 16.1-16.5 GHz, and 18.1-28 GHz. The corresponding impedance bandwidths for these bands are 2200 MHz, 400 MHz, and 9900 MHz, respectively. The simulation results demonstrate a maximum isolation of \(-\)52.72 dB. The observed discrepancies in resonant frequencies, as determined by measurements and simulations, might be attributed to several factors, including manufacturing imperfections, the SMA connectors, and disparities between the actual substrate and its modeled counterpart.  
Figure 16 displays the radiation pattern in the vertical (E) and horizontal (H) fields planes at frequencies of 9.5, 21.1, and 26.6 GHz, as both simulated and measured. The E plane is also known as the XZ plane with a phi angle of 0 degrees, and the YZ plane with a phi angle of 90 degrees is known as horizontal plane. The antenna under consideration demonstrates a virtually omnidirectional radiation pattern at a lower resonant frequency of 9.5 GHz. However, at higher resonant frequencies of 21.1 GHz and 26.6 GHz, lobes are observed in both the horizontal (H) and vertical (E) planes. The presence of multi-reflection in the measuring environment may lead to observed differences and inconsistencies between the reported measured outcomes and simulated outcomes. Overall, the suggested antenna has a consistently stable pattern.  
Figure 13: Constructed MIMO with DGS: (**a**) Frontal and (**b**) lateral view.  
Figure 14: Experimental setup. (**a**) Measurement of reflection coefficient S11 dB; (**b**) measurement of radiation pattern.  
Figure 15: _Cont._  
Figure 16: _Cont._  
Figure 15: Measure and simulated scattering parameters (dB): (**a**) S11 and S22; (**b**) S12 and S21.