# A Novel Spaceborne Sliding Spotlight Range Sweep Synthetic Aperture Radar: System and Imaging
## 6 Simulation and Discussion  
The presented approach is to be evaluated via a simulated X-band SSS-RSSAR. Within a 5 km \(\times\) 10 km (range \(\times\) azimuth) ROI, 25 targets are uniformly distributed as shown in Figure 8. The expected resolutions are in 1.00 m \(\times\) 1.31 m (range \(\times\) azimuth). The key parameters used for the SSS-RSSAR simulation are listed in Table 4, where the basic parameters are those initially set for the SSS-RSSAR observation task and the derived parameters are those calculated based on the discussions in Section 4. No antenna weighting is used for the echo simulation. Based on the simulation geometry and the basic parameters in Table 4, the DAP of the simulated SSS-RSSAR ranges from \(-\)2.49 s to 2.49 s with the CBSR variation as shown in Figure 9a. Based on the CBSR, the azimuth dependent PI array is generated as shown in Figure 9b. Figure 10a,b illustrate the echoes simulated by using and not using the CVPI technique. The while regions denote the valid data and the black regions denote no data. The constant PI used in generating Figure 10b is 190.5 \(\upmu\)s, equaling to the 13,074 th PI. While large amounts of data are lost when using the constant PI because of the transmission blockage in Figure 10b, the echo can be fully received with the CVPI technique as shown in Figure 10a. It is known that the longer the pulse width, the more serious the transmission blockage will be. Thus, the shortage of using a constant PI tends to be more serious for the SSS-RSSAR because it prefers a long pulse width. As a result, the CVPI technique has been demonstrated to be necessary and effective for the data acquisition of the SSS-RSSAR. Figure 8: Target distribution for the SSS-RSSAR simulation. \begin{table}
\begin{tabular}{c c} \hline
**Algorithms** & **Computational Load (In FLOP)** \\ \hline RDA & \(12N_{\text{aminT}}N_{\text{minT}}+10N_{\text{aminT}}N_{\text{minT}}\text{log}_{2}N_{ \text{aminT}}+10N_{\text{aminT}}N_{\text{minT}}\text{log}_{2}N_{\text{minT}}+2 N_{\text{aminT}}N_{\text{minT}}\) (2\(M_{\text{k}}-1\)) \\ \hline CSA & \(18N_{\text{aminT}}N_{\text{minT}}+10N_{\text{aminT}}N_{\text{minT}}\text{log}_{2 }N_{\text{aminT}}+10N_{\text{aminT}}N_{\text{minT}}\text{log}_{2}N_{\text{minT}}\) \\ \hline RMA & \(6N_{\text{aminT}}N_{\text{minT}}+10N_{\text{aminT}}N_{\text{minT}}\text{log}_{2 }N_{\text{aminT}}+10N_{\text{aminT}}N_{\text{minT}}\text{log}_{2}N_{\text{minT }}+2N_{\text{aminT}}N_{\text{minT}}\) (2\(M_{\text{k}}-1\)) \\ \hline \end{tabular}
\end{table} 
Table 3: Computational loads of classical imaging algorithms. Figure 10: Simulated echoes when: (**a**) using the CVPI technique; and (**b**) not using the CVPI technique. The white and black regions denote the valid data and no data, respectively. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Step** & **Parameter** & **Value** \\ \hline \multirow{8}{*}{Basic Parameters} & Referential carrier frequency \(f_{\text{c0}}\) & 10 GHz \\  & Platform velocity \(V_{\text{s}}\) & 7 km/s \\  & Platform height \(H\) & 500 km \\  & Antenna beam width \(\varphi_{\text{a}}\) & 0.41\({}^{\circ}\) \\  & Tilt angle \(\theta\) & 45.5\({}^{\circ}\) \\  & Central look angle \(\beta_{\text{c0}}\) & 44.4\({}^{\circ}\) \\  & Central slant range \(R_{\text{c0}}\) & 700 km \\  & ROI swath (\(W_{\text{r}}\times W_{\text{a}}\)) & 5 km \(\times\) 10 km \\  & Resolution (\(\rho_{\text{r}}\times\rho_{\text{a}}\)) & 1.00 m \(\times\) 1.31 m \\ \hline \multirow{8}{*}{Derived Parameters} & Sliding Spotlight factor \(\eta\) & 0.7 \\  & Bandwidth \(B_{\text{r}}\) & 189.9 MHz \\  & Pulse width \(T_{\text{P}}\) & 79.0 \(\upmu\)s \\  & Referential chirp rate \(\gamma_{0}\) & 2404 GHz/s \\  & Sampling rate \(F_{\text{s}}\) & 67.3 MHz \\  & Referential pulse interval \(PI_{0}\) & 192.8 \(\upmu\)s \\  & Sample number (\(N_{\text{r}}\times N_{\text{a}}\)) & 7344 \(\times\) 26,124 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Key parameters for the SSS-RSSAR simulation.