## 3 Results and Discussion
### Effect of Air Gap Variation on S-Parameters  
A parametric study was carried out by changing the air gap distance between the antenna structure and the OSC from 0.5 to 2 mm in steps of 0.5, as shown in Figure 8. One can notice that when the air gap was 1.5 mm, the best antenna impedance matching was achieved, and hence the OSC played an important role in the impedance matching of the antenna.  
Figure 6: (**a**) Simulated radiation patterns of the proposed antenna with and without OSC downlink for E-plane, (**b**) for H-plane, (**c**) measured radiation patterns of the antenna structure downlink for E-plane and H-plane, and (**d**) simulated 3D radiation pattern for the proposed antenna.  
Figure 7: Simulated dependence of the S-Parameters (S11) of the proposed CPW-fed antenna on the changes in patch antenna width (W5).  
In order to understand the operating mechanism of the antennas structure, the current distribution of the proposed antenna, with and without a solar cell, is demonstrated in Figure 9.  
Table 3 presents the performance of the proposed design in terms of bandwidth, gain, application, and insolation compared to that reported in the literature. It was observed that the proposed design performed well when it came to 100% insolation for satellite communications.  
Figure 8: The effect of the antenna on the OSC gap variation on the S11 of the proposed CPW antenna.  
Figure 9: Current distribution of the antenna with OSC (**a**) and without OSC (**b**).  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Reference** & **Bandwidth (GHz)** & **Max. Gain (dB)** & **Application** & **Insolation \%** \\ \hline
[9] & 2.4–2.5 & 3.7 & Airborne communication nodes, wireless sensor networks. & 100\% \\
[10] & 2.3–3.2 & 3 & Radio link with solar & - \\
[11] & 2.45–2.5 & 3.5 & Wireless sensor network & 94.7\% \\
[13] & 2.45–2.5 & 5.15 & Small satellite & 70\% \\
[15] & 10.7–12.7 & 26.16 dB & Satellite communications & Not 100\% \\
[16] & 5.66–5.91 & 7.8 & WiMAX & - \\ proposed design & 5–16 & 5.90 & Satellite communications & 100\% \\ \hline \hline \end{tabular}
\end{table}
Table 3: Comparison of the proposed antenna with those reported in the literature.  
The simulated and measured return loss results for the CPW design are shown in Figure 10. Considering the \(-10\) dB return loss as a reference point, the operating frequency ranges for both results were almost similar. There was been a mismatch between the measured and simulated results, which might have originated from the lab conditions, calibration errors, and fabrication process with the prototyping machine when considering the size of the antenna structure. It can be concluded from the numerical and experimental results that the proposed antenna structure operated in the Ku band frequency regime. Due to the unavailability of OSC fabrication facilities, just the antenna was fabricated and measured without a solar cell. The reason for the difference between the measured and simulated S\({}_{11}\) results may be due to the fabrication tolerance and/or substrate and soldering losses. The antenna had a relatively lower efficiency below \(10\) GHz, and with the addition of the solar structure, the antenna efficiency also reduced a bit. Therefore, that caused the realized gain to be reduced to below \(10\) GHz. As the antenna had a wide bandwidth with a relatively high gain with the simple size, this made the proposed structure suitable (beside satellite application) for many other wireless applications, including environmental monitoring systems and vehicular communication. Therefore, it can be efficiently used for fixed-satellite-services (FSS) in an operating frequency range from \(11.7\) to \(12.22\) GHz.