# Robust Space Time Adaptive Processing Methods for Synthetic Aperture Radar
## 6 Measured Data Results  
The algorithm is further validated by flight experiments. The data was collected by an X-band multi-channel airborne SAR whose bandwidth is 200 MHz and the theoretical resolution is 1 m \(\times\) 1 m. The aircraft was flying along the southeast direction. The imaging area was located at 30 km, and the squint angle was about 15\({}^{\circ}\). The jammer fixed near the imaging area was about 3\({}^{\circ}\) away from the main beam. The interference type transmitted by the jammer is wideband blanket jamming. The interference-to-noise (JNR) ratio in the original SAR image is more than 15 dB before interference cancellation. The total synthetic aperture time is 6.2 s, and the DOA of the interference varied about 2.5\({}^{\circ}\) during the period. Figure 7 is the SAR image before interference suppression and the ground echo was completely covered by the interference.  
Figures 8 and 9 are SAR images processed by conventional piecewise STAP and piecewise constrained STAP, respectively. It can be seen that the proposed algorithm can effectively suppress interference and improve azimuth focusing performance compared with the original algorithm.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{2}{c}{**Theoretical Azimuth Resolution**} & \multicolumn{2}{c}{**1.19 m**} \\ \hline \hline \multirow{2}{*}{**Item**} & \multicolumn{1}{c}{**Number of Sub-Apertures**} & \multicolumn{1}{c}{**Conventional Method**} & \multicolumn{1}{c}{**Proposed Method**} \\ \cline{2-4}  & M = 16 & 1.48 m & 1.27 m \\ \cline{2-4}  & M = 32 & 1.49 m & 1.27 m \\ \cline{2-4}  & M = 64 & 1.47 m & 1.27 m \\ \hline \multirow{2}{*}{
\begin{tabular}{c} Simulation Azimuth \\ PSLR/ISLR \\ \end{tabular} } & M = 16 & \(-\)21.9 dB / \(-\)16.4 dB & \(-\)25.2 dB / \(-\)22.3 dB \\ \cline{2-4}  & M = 32 & \(-\)22.2 dB / \(-\)17.7 dB & \(-\)25.2 dB / \(-\)22.3 dB \\ \cline{2-4}  & M = 64 & \(-\)22.8 dB / \(-\)17.9 dB & \(-\)25.2 dB / \(-\)22.3 dB \\ \hline \hline \end{tabular}
\end{table}
Table 2: Evaluation results of point targets simulation.  
Figure 7: SAR image before interference suppression.  
In order to observe image quality improvement of the proposed algorithm more clearly, Figure 10 shows two local areas in the image. It can be seen that the proposed algorithm can significantly improve the focusing effect of the image.  
Figure 11 shows the comparison of the point target profile, and the Hamming window is used in the SAR process in order to reduce the sidelobe levels.  
Figure 8: SAR images processed by conventional piecewise STAP.  
Figure 10: Detailed results of a local area: (**a**) Result of conventional STAP (M = 16); (**b**) Result of PC-STAP (M = 16).  
Figure 9: SAR images processed by piecewise constrained STAP.  
To further evaluate the performance of the proposed algorithm, the measured parameters of PSLR, ISLR, and spatial resolution (3 dB width) of the corner reflector in the SAR image were calculated, and the results are listed in Table 3. We can find that the performance parameters of the proposed algorithm are obviously superior to that of the conventional piecewise method.