# Tilted Beam Fabry-Perot Antenna with Enhanced Gain and Broadband Low Backscattering
## 3 Simulation Results and Experimental Validation
### Scattering Results
One significant advantage of using these antennas is that their form factor is smaller as compared with horn antennas, and hence the practical monostatic RCS measurement (which is in fact a quasi-monostatic environment) is closer to the ideal simulated (pure) monostatic environment. Figure 17a,b presents the comparison between simulated and measured RCS reduction for x-pol and y-pol of the incident wave, respectively. It can be witnessed that the achieved measured reduction values satisfactorily follow the simulated performance on all frequency points, and hence the measurement can be considered to be a successful validation of the design concept. Figure 17c shows one scenario of the measurement setup. The proposed as well as reference antennas were terminated with a matched impedance for scattering measurements. To further elaborate, simulated vs. measured RCS reduction values at the measured frequency points are listed in Table 3. The absolute difference between simulated and measured average RCS reduction is less than 0.5 dB for both polarizations of the incident wave. Figure 17: Simulated vs. measured monostatic RCS reduction plotted at discrete frequency points. (**a**) x-Pol incident wave; (**b**) y-Pol incident wave; (**c**) RCS measurement setup. (AUT, antenna under test). To show angular (\(\pm 90^{\circ}\)) stability of the design, the response of monostatic RCS against oblique angle incidences for orthogonal polarizations has also been investigated. For the yoz principal plane with x-pol incident wave, Figure 18a displays simulation vs. measurement plot of normalized monostatic RCS angular response for the reference antenna, and Figure 18b displays the same for the proposed prototype antenna. Likewise, for xoz plane with y-pol incident wave, Figure 19a shows simulation vs. measurement plot of normalized monostatic The RCS angular response for the reference antenna, and Figure 19b displays the said plot for the prototype antenna. All these patterns have been plotted at 8.8 GHz. For the yoz plane, about \(\pm 13^{\circ}\) of RCS reduction is achieved, while this value increases to \(\pm 18^{\circ}\) for the xoz plane. For both planes, the maximum value of RCS reduction exceeds 27 dB, and therefore this means that significant portion of the incident wave is being absorbed at the resistive surface of the antenna. The measured results are in sufficient agreement with the simulation results, and the discrepancy witnessed can be attributed to measurement setup issues. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**S. No.**} & \multirow{2}{*}{
\begin{tabular}{c} **Frequency Points** \\ **(GHz)** \\ \end{tabular} } & \multicolumn{5}{c}{**RCS Reduction (dB)**} \\ \cline{3-6}  & & **x-pol** & **x-pol** & **y-pol** & **y-pol** \\  & & **Simulated** & **Measured** & **Simulated** & **Measured** \\ \hline
1. & 7.5 & 11.67 & 12.4 & 10.92 & 10.87 \\
2. & 8 & 13.99 & 18.12 & 14.69 & 14.62 \\
3. & 8.8 & 31.53 & 26.65 & 27.77 & 22.09 \\
4. & 10 & 15.66 & 20.32 & 15.27 & 22.23 \\
5. & 12.6 & 18.68 & 21.49 & 17.76 & 19.82 \\
6. & 14 & 18.38 & 11.48 & 19 & 18.37 \\ \hline Average RCS Reduction (dB) & 18.32 & 18.41 & 17.57 & 18 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Simulated vs. measured RCS reduction values at measured frequency points. Figure 18: Normalized monostatic RCS angular response for the yoz plane with x-pol incident wave at 8.8 GHz. (**a**) Reference antenna; (**b**) Proposed antenna.