## 7 Equivalent Real Data BiSAR Experiment Based On BeiDou Navigation Satellite  
In order to further verify our frequency domain imaging algorithm, we designed and built a satellite-ground SAR system to carry out equivalence experiment. The real data experiment is organized as Figure 15. In the experiment, BeiDou navigation satellite with inclined geosynchronous orbit (IGSO) serves as the transmitter operating in the L-band. The transmission signal adopts binary phase shift keying (BPSK) modulation mode with the bandwidth of 20.46 MHz. In our experiment, we found that the reflected signal was too weak to obtain a SAR image. Therefore, we set a repeater in the illuminated scene to amplify the reflected signal to improve the signal-to-noise ratio (SNR). As shown in Figure 15a, the coordinate system O-\(XYZ\) is consistent with the definition in Section 2.1. In the scene flat, the antenna R receives the enhanced signal from the repeater. A few tens of  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Target**} & \multicolumn{3}{c}{**Range**} & \multicolumn{3}{c}{**Azimuth**} \\ \cline{2-7}  & **PSLR (dB)** & **ISLR (dB)** & **IRW (m)** & **PSLR (dB)** & **ISLR (dB)** & **IRW (m)** \\ \hline
2 & \(-13.476\) & \(-10.895\) & \(9.954\) & \(-12.742\) & \(-10.010\) & \(9.501\) \\
4 & \(-13.446\) & \(-10.886\) & \(9.954\) &  
meters away from antenna R, there exists antenna D which receives the direct signal from BeiDou navigation satellite for synchronization. The received echo is transferred to the computer for focusing processing.  
It should be noted that our GTLR-BiSAR focusing algorithm is proposed for the bistatic configuration of geostationary transmitter with LEO receivers, where the emitter is static and the LEO receiver is moving. Our developed formalism can be applied to such a geometry where BeiDou navigation IGSO satellite is a moving emitter source with a static ground receiver. Therefore, our proposed method can be demonstrated by the real data experimental results to a certain extent. Figure 15b shows our experiment conducted on the roof. Some main parameters are given in the following Table 5.  
Different from the traditional spaceborne SAR satellites, BeiDou IGSO satellite transmits BPSK continuous navigation signal. Firstly, we should transform the continuous signal to segmentation form according to the coarse/acquisition (C/A) code. Then we obtain the two dimensional echo matrix shown in Figure 16a. Then we apply our proposed method to focus the image, the result in Figure 16b-d validate the effectiveness of our algorithm. The theoretical range resolution is 19.40 m, and the result of our method is 20.99 m. The theoretical azimuth resolution is 4.55 m, and the result of our method is 4.62 m. The non-ideal azimuth pulse response is caused by the system errors. It should  
Figure 15: The geometry and ground receiving equipment of our equivalence verification experiment. (**a**) The geometry of satellite-ground SAR system. (**b**) Setup of the experiment we conducted on the roof.  
\begin{table}
\begin{tabular}{c c} \hline \hline
**Parameters of BeiDou Navigation IGSO Satellite** & **Value** \\ \hline Orbit Height of BeiDou IGSO satellite & 35,786.00 km \\ Inclination of BeiDou IGSO satellite & 55\({}^{\circ}\) \\ Eccentricity of BeiDou IGSO satellite & 0 \\ Transmitted Frequency & 1268.52 MHz (L-band) \\ Transmitted Bandwidth & 20.46 MHz \\ Pulse Repetition Frequency & 1000 Hz \\ Transmitter Velocity & 2533.42 m/s \\ \hline \hline \end{tabular}
\end{table}
Table 5: Main experiment parameters of BeiDou IGSO satellite.  
be noted that the range compression is operated according to the BPSK code, which is different from the chirp signal. Essentially, they are convolution operations to realize the signal autocorrelation.