# Analysis of the Dihedral Corner Reflector's RCS Features in Multi-Resource SAR
## 4 The RCS Features of the CR Array in Multi-Resource SAR  
### The RCS Reduction Trend and Systematic Bias Analysis  
Experimentally measuring the RCS reduction with respect to the deviation angle under real SAR data provides more realistic results compared to theoretical derivations. However, challenges may still exist, such as stringent experimental conditions and environmental background noise. The measured RCS in SAR data is typically calculated using the integration method [20]. Figure 5a,c illustrate the RCS mean and variance of the CR array calculated using the integration method under the Sentinel and TSX data. a few values that are influenced by environmental influences or alignment deviations are excluded. Figure 5a,c also depict the RCS reduction with the deviation angle \(\beta\), and the solid lines represent the values calculated by the proposed model. The model proposed does not consider factors like the panels' dielectric constants, leading to the slight overestimation of the RCS. Figure 6b,d illustrate the difference between the measured RCS and model values under the Sentinel and TSX data. The system deviations of most CRs (nearly 70%) are concentrated within 0.5-2 dBm, and there is no significant difference observed among CRs with different panel types. Overall, the RCS reduction trends in the measured results align with the trends from the model. In the Sentinel data, the variance of the RCS increases with the reduction in the CRs' panel size. The variances of the dihedral CR with the semi-circular panel with side lengths of 0.6 m and 0.8 m are approximately 2 and 1 dBm, respectively. It means smaller-sized CRs experience larger impacts from environmental noise due to a relatively lower signal-to-clutter ratio (SCR). The observed discrepancy between the measured and modeled RCS follows the same pattern with RCS variance. For the TSX data, the CR's panel size change has minimal impact on RCS variance and the disparities between the measured and modeled values. Most CRs exhibit RCS variances within 0.5 dBm, attributed to the high signal-to-noise ratio in the TSX spotlight mode. The SCR for the dihedral CR with a 0.6 m panel size can reach 30 dB maximumly. Consequently, the discrepancies between the measured and modeled RCSs are more likely attributed to the CRs' inherent qualities or environmental influences. For instance, the dihedral CR with a semi-circular panel of 0.8 m loses signal in descending TSX data, and \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline  & & & & & & \multicolumn{3}{c}{**Sentinel**} & \multicolumn{3}{c}{**TSX**} \\ \cline{4-10}  & **Number** & **Type** & **Length** & **Tilt** & **Angle** & \(\beta\) & \(\beta\) & \(\beta\) & \(\beta\) & \(\beta\) & \(\Delta\beta\) \\  & & & **(m)** & **a (\({}^{\circ}\))** & **(084** & **(011** & **(C)** & **(AC)** & **(DES)** & **(C)** \\ \hline First group & DR1\(-\)DR2 & semi-circular panel & \(\Phi=0.6\) & 0 & 1 & 13 & 12 & 7 & 16 & 9 \\  & DR3 & square panel & a = 0.4 & 0 & 1 & 13 & 12 & 7 & 16 & 9 \\ \hline Second group & DR4\(-\)DR5 & semi-circular panel & \(\Phi=0.6\) & 10 & \(-9\) & 3 & 6 & \(-3\) & 6 & 3 \\  & DR6 & semi-circular panel & \(\Phi=0.8\) & 10 & \(-9\) & 3 & 6 & \(-3\) & 6 & 3 \\ \hline Third group & DR7 & semi-circular panel & \(\Phi=0.6\) & 15 & \(-14\) & \(-2\) & 12 & \(-8\) & 1 & 7 \\  & DR8 & semi-circular panel & \(\Phi=0.8\) & 15 & \(-14\) & \(-2\) & 12 & \(-8\) & 1 & 7 \\ \hline Fourth group & CR1\(-\)CR2 & \
\begin{tabular}{c} Triangular CR \\ (ascending) \\ \end{tabular} & 1 = 1.2 & 20 & \(-9\) & 3 & 6 & & & & \\  & CR3\(-\)CR4 &
\begin{tabular}{c} Triangular CR \\ (descending) \\ \end{tabular} & 1 = 1.2 & 20 & & & & \(-3\) & 6 & 3 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The types of CR and corresponding axis deviation angles. the remaining two observations in ascending TSX data exhibit 2.5-5 dBm discrepancies compared to theoretical values.