## 3 Experimental Studies  
Nriet-SAR (SAR of Nanjing Research Institute of Electronic Technology), an airborne dual-band (L, X) multichannel polarimetric SAR sensor, was applied to conduct the experiment [33]. The principal parameters are shown in Table 3.  
The geometric relationship between the SAR sensor and the jammer is briefly illustrated in Figure 11, in which the radar moves along a linear flight path with a typical flight height of 7000 m, and the jammer is in the SAR imaging area. Figure 12 shows the optical image (from Google Earth) of the experimental area in Weinan City, Shanxi, China. The blue icon in the middle of Figure 12 indicates the location of the jammer (source of radiation) used in the experiment, and the blue arrow shows the antenna orientation of the transmitting and receiving antennas. Additionally, the flight direction of the Nriet-SAR platform is from south to north (from right to left in Figure 12). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Operation** & **Input Data Size** & **Output Data Size** & **Time Cost (us)** \\ \hline N times FFT & \(N\times K\) & \(N\times K_{2}\) & \(N\times K_{2}/128\times 4\) \\ N times \(K_{2}\) points dot product & \(N\times K_{2}\) & \(N\times K_{2}\) & \(N\times K_{2}/128\times 2\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The major time cost of our method. is triggered to generate the jamming signals. The jamming signals are transmitted by the transmitting antenna to the radar after being amplified by the power amplifier. Figure 14: The schematic diagram and processing chain. (**a**) Schematic diagram. (**b**) Processing chain. Figure 13: The jammer, the transmitting antenna, and the receiving antenna. To verify the effectiveness of our proposed method, two linear SAR trajectories have been designed to observe the imaging area shown in Figure 12 in this experiment, in which the parameter configuration of SAR is shown in Table 1. In the first linear SAR trajectory, the jammer is turned off, which can be seen as a set of comparative experiments, so we can achieve a perfect SAR image of the imaging area with commonly used SAR imaging algorithms. In the other linear SAR trajectory, the jammer is turned on and transmits jamming signals to the receiving antenna of SAR according to the processing chain shown in Figure 14.  
In this airborne experiment, the original SAR data obtained by Nriet-SAR are processed using along-track DCC. Figure 15 shows the SAR imaging result without jamming, and Figure 16 shows the SAR image with jamming. As we can see from Figures 15 and 16, when the jammer is turned off, SAR can perfectly reconstruct the SAR image of the ground features in the imaging area. However, it can be clearly found that parts of the ground features are not clearly visible and that they are seriously influenced by the jamming signals in Figure 16.  
To eliminate the influence of the jamming signals and to reconstruct the SAR image of the imaging area, a cosine similarity-based DCC method has been applied in the airborne  
Figure 16: SAR image with jamming. Figure 15: SAR image without jamming. experimental data. Figures 17 and 18 show the DCC images, while the IPSR error of Figure 18 is set to \(18^{\circ}\) on purpose, and the IPSR of Figure 17 is relatively precise. As we can see from Figure 17, most of the interference images have been eliminated, and the ground features have become visible after accurate cosine similarity-based along-track DCC. Due to the set of the deliberate IPSR errors of \(18^{\circ}\), which can be considered as the wrong estimations of the IPSR, Figure 18 suffers from the slight influence of the jamming signals. However, a dark strap still appears in the middle of Figures 17 and 18 along the range direction of the jammer (from top to bottom), which is consistent with our analysis in Section 2.5. Compared with the SAR image without jamming in Figure 15, the ground features in the imaging area can still be well reconstructed with our proposed method, while the SAR is severely influenced by the jammer.