## 5 Experimental Results
### Measured Experiment  
In this paper, the real data collected by a four-channel airborne X-band SAR system are used to verify the performance of the proposed method. The system parameters are shown in Table 5. The four channels are equally spaced in the azimuth direction, and the working mode of one-transmitter and four-receiver is adopted. In this paper, the target signal extracted after clutter suppression is imaged. The flight platform and cooperation targets are shown in Figure 9a,b, respectively. There are three electric tricycles as cooperative targets in the experiment. Each target is equipped with a corner reflector, and a GPS device is installed to record the real-time position and speed information of the target as the true value of the target movement. The imaging result of the stationary scene without processing of GMT is shown in Figure 10a. The magnified images of T1-T3 are shown in Figure 10b-d, respectively. As can be seen from the figure, targets moving along the radial direction are defocused and appear displaced in azimuth from their original position. Taking the target T1 as an example, the processing results of each step of the proposed method are analyzed. The target signal after clutter suppression is shown in Figure 11a. Figure 11b,c are the two-dimensional time domain signal and range-Doppler domain signal after RCMC, respectively. It can be seen that the target energy is basically corrected to the same range cell after Hough-SOKT. Figure 11d is the \(F_{0}\)-\(F_{1}\) parameter plane constructed by the proposed method, and Figure 11e is the slice along \(F_{0}\) at the peak of the parameter plane obtained by the two methods. Obviously, the peak value obtained by the proposed method is larger, which verifies that the proposed method can can obtain higher coherent accumulation gain. Figure 11f,g show the refocused results of T1 by two methods, the proposed method has better focusing. Figure 11h,i are slices in the range and azimuth directions, from which it can be seen that the focusing of the target in the azimuth has been significantly improved. In Figure 11f-i, the image is interpolated 16-fold in azimuth and range directions. The results verify that a better focusing performance can be obtained by the proposed method. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Parameter** & **Value** & **Parameter** & **Value** \\ \hline Wave band & X & Pulse duration time & 5 μs \\ Range bandwidth & 1800 MHz & Pulse repetition frequency & 2000 Hz \\ Range sampling frequency & 2000 MHz & Center slant range & 7 Km \\ Target velocity & \textless{}3 m/s & Synthetic aperture time & 5 s \\ \hline \hline \end{tabular}
\end{table} 
Table 5: The parameters of X-band airborne SAR system. Figure 9: Flying platform and cooperation targets. (**a**) Flying platform. (**b**) Cooperation targets. Figure 11: Processing result of T1. (**a**) Target signal after clutter suppression. (**b**) Hough+SOKT RCMC; (**c**) Range-Doppler domain. (**d**) \(F_{0}\)–\(F_{1}\) parametric plane. (**e**) \(F_{0}\) estimate. (**f**) Imaging by proposed method (16\(\times\) upsampling). (**g**) Imaging by KT-CICPF (16\(\times\) upsampling). (**h**) Slice in range. (**i**) Slice in azimuth. Figure 10: Image of the stationary scene without processing of GMT. (**a**) Image of the stationary scene (the yellow pentagram indicates the target’s relocation position). (**b–d**) Magnified images of moving targets (defocused). To verify the adaptability of the algorithm, the same processing is used for T2 and T3 as for T1. Figure 12 shows the refocused results of the three targets by three methods. The magnified images of moving targets without processing of GMT are shown in Figure 12a-c, respectively. The refocused results by the KT-CICPF method of T1-T3 are shown in Figure 12d-f. The results by the proposed method are given in Figure 12g-i. As can be seen from the figure, the focusing effect of the proposed method on T1-T3 is superior to that of KT-CICPF method.