# Pentaband Dual-Polarized Antenna for Multiservice Wireless Applications
## 3 Experimental Validation  
The MIMO antenna prototype has been fabricated on an FR-4 substrate and underwent testing. The fabricated photograph of the antenna and the simulation and measurement of S-parameters are shown in Figure 10. The S-parameter was measured using an Anritsu S820E vector network analyzer (VNA). In the measurement process for the proposed antenna, the first step involved calibration of the VNA using a standard calibration kit to ensure accurate measurements. The VNA calibration process accounted for the losses and delays associated with the cables and connectors used in the measurement setup. After calibration, the S-parameter was measured by connecting the antenna to the VNA through a coaxial cable and performing a frequency sweep from 2 GHz to 9 GHz. The measurement results were then compared with the simulated S- parameter to validate the design. The  
Figure 8: ECC of the quad-port antenna.  
Figure 9: DG of the quad-port antenna.  
simulation predicts impedance bandwidths of 0.15 GHz, 0.3 GHz, 0.85 GHz, 0.3 GHz, and 0.5 GHz for the 5 resonance bands at 1.55 GHz, 2.5 GHz, 5.2 GHz, 7.3 GHz, and 8.15 GHz, respectively. Also, at the third resonance frequency (5.2 GHz), there are notable differences between the simulated and measured results, which could be attributed to the presence of the ground slit. Manufacturing tolerances in the ground slit's production process could lead to variations in its width and length, resulting in changes in the electromagnetic field distribution within the structure. These changes may, in turn, impact the reflection and transmission of signals through the device, leading to discrepancies between the simulation and measurement results. Although the measured resonance bands deviate slightly from the simulation, the results indicate the feasibility of the proposed antenna for multiple-frequency bands.  
The 3 dB ARBW and peak gain were also evaluated, and the simulation and measurement results are shown in Figure 11. At 1.55 GHz and 2.6 GHz, the simulated axial ratios are 1.05 and 1.65, respectively, and the measured axial ratio is in good agreement with the simulation results. Moreover, the peak gain values for the 5 resonance frequency bands are 0.55 dBi, 2.5 dBi, 3.65 dBi, 3.85 dBi, and 3.9 dBi, respectively. Furthermore, the measured gain is relatively similar to the simulated gain.  
Figure 10: Fabricated prototype and S-parameter validation comparison. (**a**) Top, (**b**) bottom, and (**c**) simulated and measured S-parameter comparison.  
The directional properties of the MIMO antenna proposed in this paper were evaluated by measuring and simulating its radiation patterns at various frequencies. The results, as shown in Figure 12, demonstrate that the antenna exhibits bidirectional and omnidirectional patterns in both the E-plane and H-plane at lower frequencies. At higher frequencies, the E-plane pattern displays a main lobe in the +z direction, while the H-plane deviates slightly from +z and has a null at 30\({}^{\circ}\). At 2.6 GHz, both the E-plane and H-plane patterns are in the -z-direction. For the other 2 frequencies, there are deviations from the +z direction, and a sharp null is observed between 0\({}^{\circ}\) and 30\({}^{\circ}\). Overall, the directional properties of the antenna make it suitable for use in a variety of wireless applications that require reliable and consistent signal transmission and reception across multiple frequency bands.  
Figure 11: Quad-port antenna simulated axial ratio and gain comparison with measured results.  
Figure 12: _Cont._