## 3 Simulation and Experimental Results
As evident from Figure 9a,b, an agreeable correlation is found between the simulated and measured results; in fact, the measured suppression performance is superior for most of the frequency points. The details of tested frequencies with a comparison between simulation and measured RCS suppression levels are exhibited in Table 2. The measured mean suppression surpasses the simulated values. From these measurements, it can be asserted that the design verification stands as successful. The monostatic RCS was also investigated as a function of incidence angle (\(-90\) to \(+90\)) to determine the angular stability of the proposed design. Figure 10a,b show normalized y-z plane plots for VP incident wave, respectively, for reference antenna and proposed antenna. Similarly, Figure 11a,b show normalized x-z plane plots for HP incident wave, respectively, for reference antenna and proposed antenna. Measured results of the above are presented along with, and depict, a satisfactory correlation with the simulation results. All of these results were plotted at 10 GHz. From Figures 10 and 11, RCS reduction occurs over about \(\pm 15^{\circ}\) angular span. All presented RCS results are for antennas terminated with matched load. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Ser.**} & \multirow{2}{*}{
\begin{tabular}{c} **Tested** \\ **frequencies** \\ **(GHz)** \\ \end{tabular} } & \multicolumn{4}{c}{**RCS Suppression (dB)**} \\ \cline{3-6}  & & \multicolumn{2}{c}{**VP Incident Wave**} & \multicolumn{2}{c}{**HP Incident Wave**} \\ \cline{3-6}  & & **Simulation** & **Measurement** & **Simulation** & **Measurement** \\ \hline
1. & 7.5 & 9.32 & 11.49 & 9.44 & 12.92 \\
2. & 8 & 9.15 & 12.72 & 9.27 & 13.73 \\
3. & 8.8 & 9.93 & 18.48 & 10 & 18.3 \\
4. & 10 & 7.43 & 12.5 & 7.66 & 11.71 \\
5. & 12.6 & 8.61 & 13.16 & 9 & 14.51 \\
6. & 14 & 17.02 & 16.95 & 18.78 & 16 \\ \hline Mean RCS Suppression (dB) & 10.24 & 14.22 & 10.69 & 14.53 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: RCS suppression values at tested frequencies. Figure 9: Simulation vs. measurement results of monostatic RCS suppression presented at different frequency points. (**a**) VP wave incidence. (**b**) HP wave incidence. (**c**) Measurement setup. In Figure 12, the simulated monostatic RCS angular responses of the reference and proposed antennas are presented for some more frequencies. Figure 12a illustrates the y-z plane RCS plots for a VP incident wave at 7.6 GHz, while Figure 12b illustrates the x-z plane RCS plots for an HP incident wave at 7.6 GHz. Similarly, Figure 12c illustrates the y-z plane RCS plots for a VP incident wave at 14 GHz, while Figure 12d illustrates the x-z plane RCS plots for an HP incident wave at 14 GHz. For the 7.6 GHz frequency, the RCS reduction in both planes occurs over an angular span of \(\pm 22^{\circ}\), and it increases to \(\pm 28^{\circ}\) at 14 GHz. It is inferred that as the broadside RCS reduction increases, the angular span over which the RCS reduction is achieved, increases as well. Furthermore, it can be observed from Figures 10-12 that in comparison to the reference antenna, the low RCS performance of the proposed antenna gets impaired towards wider off-broadside angles. In fact, the reflectivity even increases at too far-off angles. This increase may be attributed to the vertical dimension of the proposed antenna, as it is a Fabry-Perot cavity, while the reference antenna is a single layer planar antenna. Thus, it is important to mention that although the proposed antenna's main beam (radiation) is deflected towards off-broadside direction, the wideband low RCS performance of the proposed antenna is dominantly towards broadside angles only. Furthermore, as explained by the working of the unit cell in Section 2, the off-broadside peak radiation was achieved by implementing the phase gradated PRS, while the wideband broadside RCS reduction is a result of the PRS backed AFSS.