## 4 Test Validation  
### Setup of Experimental Scenarios  
To verify the proposed method (i.e., the dynamic dual-antenna method for determining the directions of spoofing signal sources), we performed real-time data acquisition and analysis. Additionally, we utilised a spoofing signal source to simulate satellite navigation signals and conducted satellite navigation spoofing on the vehicle-mounted antennas. To ensure the reliability of the reference system, only the signals on B\({}_{1}\) and B\({}_{3}\) frequency points of BeiDou were spoofed. GPS observation data are reserved for reliability. The latitude, longitude, and elevation of the observation site are approximately written as (112.99 deg, 28.23 deg, 60 m).  
As depicted in Figure 6, two antennas and an MIMU were firmly connected to the carrier; the \(X\)-axis of the MIMU body coordinate system coincided with the \(X\)-axis defined for the carrier coordinate system; the \(o-x_{MINU}^{b}y_{MINU}^{b}\) plane of the MIMU body coordinate system coincided with the \(o-x^{b}y^{b}\) plane of the carrier body coordinate system; the \(Y\)-axis of the MIMU body coordinate system was parallel to the \(Y\)-axis defined for the carrier coordinate system. To obtain the high-precision position and attitude information of the carrier, we installed a high-precision INS in the vehicle body, where the \(o-x_{INS}^{b}y_{INS}^{b}\) plane of the MIMU body coordinate system coincided with the \(o-x^{b}y^{b}\) plane of the carrier body coordinate system and the \(Y\)-axis of the MIMU body coordinate system was parallel to the \(Y\)-axis defined for the carrier coordinate system.  
Real-time observation data were collected with the Sinan dual-antenna board. The high-precision attitude information associated with the reference position was obtained via the integration of high-precision inertial navigation and satellite navigation. The vehicle hovered in a nearly horizontal field with the circle-shaped trajectory.  
In the experiments, the carrier-phase error of the Sinan dual-antenna board was less than 0.05 rad; signals on BeiDou B\({}_{1}\) and B\({}_{3}\) frequency points were observed; the MIMU error was less than 10 deg/h; POS620 was applied for high-precision inertial navigation, with an error being less than 0.012 deg/h. Detailed information is shown in Tables 1-3.  
Figure 6: Experimental device.  
In this study, experiments 1 and 2 were conducted to determine the two-dimensional direction of long-distance BeiDou satellite signal sources in synchronous orbits and a spoofing signal source in the short distance, respectively, to verify the accuracy of the system in determining the two-dimensional directions of signal sources at different distances. Experiment 3 was conducted to simulate the accuracy of determining the two-dimensional direction of a 10 km spoofing signal source in the background environment so as to illustrate the working accuracy of the model in the real-world environment.  
The position of the spoofing device in the \(\mathbf{b}_{0}\) system was calculated using the method proposed in this study (i.e., the dual-antenna GNSS/MIM-based method for determining the two-dimensional directions of satellite navigation signal sources). The high-precision attitude position information of the carrier was obtained based on the vehicle-mounted high-precision INS combined with the inter-station differential method. Using such information, we calculated the DOA of the satellite navigation signal source to determine its position. The computational accuracy of the proposed method was obtained by calculating the error between the real and calculated values.