# Dual-Frequency Signal Enhancement Method of Moving Target Echoes for GNSS-S Radar
## 3 Simulation and Experimental Results
### Experiments  
In order to further prove the effectiveness of the proposed method, a field test was carried out in Beijing Environmental Science and Technology Park using the experiment equipment shown in Figure 2. The experimental site is shown in Figure 17. The B1 and B3 frequency signals of the BDS satellite are selected as the illumination source. Figure 18 shows the experimental scene, with the detection equipment installed on the roadside to detect cars passing by at high speeds. During the experiment, the detected target 1 was a small car with a speed of approximately 45 km/h. The detected target 2 is an SUV vehicle with a speed of approximately 35 km/h. The two cars are traveling in the same direction, from south to north. Figure 17: Illustration of the experimental site. Figure 18: Experiment scene. Figure 19 shows the distribution of the BDS satellites received at the experimental site. In the figure, the receiver is located at the center, and two cars pass from south to north. In order to achieve target detection, satellites that form a backscattering geometric relationship are selected from visible satellites as the illumination source. Four typical satellites that constitute backscatter are selected as the illumination sources for detection. The information on the four satellites is shown in Table 3.  
Figure 20 shows the original 2D data after the signal is compressed. In the figure, the horizontal axis R represents the bistatic distance, and the vertical axis tm represents slow time. Since the navigation satellite signal scattered by the car is extremely weak, the target information cannot be directly observed without accumulation in the slow-time dimension. In order to compare the accumulation effects of single-frequency and dual-frequency processing methods, the signal accumulation images obtained by the two methods are listed below. Firstly, the single-frequency signal is used for coherent accumulation processing to obtain the target echo signal trajectory in the \"time-distance\" domain. Figure 21 shows images of echo traces of B1 frequency signals of four satellites: No. 1, No. 3, No. 6, and No. 38, and Figure 22 shows images of echo traces of B3 frequency signals of these four satellites. The images show that the accumulation effect of single-frequency signals is limited, which is due to the effect of the target velocity in the single-frequency echo. The maximum coherent accumulation time is 6 ms, and the signal becomes weaker when the accumulation time is further increased. After accumulation, only the echo trajectories of satellite No.38 are faintly visible, while the echo trajectories of satellites No.1, No.3, and No.6 are almost invisible. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Satellite ID** & **Elevation/\({}^{c}\)** & **Azimuth/\({}^{c}\)** & **Bistatic Angle \(\alpha\)/\({}^{c}\)** \\ \hline
1 & 35 & 140 & 51 \\
3 & 44 & 189 & 45 \\
6 & 62 & 234 & 74 \\
38 & 49 & 169 & 50 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Position information on the selected four satellites. Figure 19: Distribution and relative position of the BDS satellites. For the satellite echo signals in Figures 21 and 22, the SNR curve of the signal is obtained by counting the SNR row by row, as shown in Figure 23. Figure 23a is the SNR of the echo of the B1 signals, and Figure 23b is the SNR of the echo of the B3 signals. It can be seen that except for the No. 38 satellite, which has a higher SNR (the highest value is about 5 dB), the SNR of other satellites is very low. Then, the scattering signals of B1 and B3 frequencies of BDS satellites No. 1, No. 3, No. 6, and No.