## 3 Results and Analysis of the Ground Test
### Performance Test of the Orthographic Stabilization Platform  
#### 3.1.1 Analysis of Key Indicators  
The purpose of the orthographic stabilization platform is to ensure that the optical axis of the visible light camera is always perpendicular to the earth's surface, ensuring clear imaging quality and accurate positioning of the target object. Therefore, its key indicator is stability accuracy.  
In a stable state, the image stabilization platform should compensate for the swaying and undulating motion of the carrier body and maintain the spatial stability of the optical axis. Considering the typical indicators of the aircraft (flight altitude of 3000 m, speed less than 300 km/h, fuselage roll of \(\pm 10\)\({}^{\circ}\), cycle of 7 s), in order to meet the task of detecting ground targets and effectively concatenate the photos taken by the camera, the optical axis fluctuation must be limited to a certain range to ensure that the overlapping area of adjacent two frames of images is not less than \(1/4\). Considering the aircraft's speed and photography frequency (one frame of image per second), the aircraft's travel per second is 83.3 m. If  
\begin{table}
\begin{tabular}{l l c} \hline \hline
**Technical Indicators** & **States** & **Indicator Values** \\ \hline Operating Frequency & Transmission & 14 GHz-14.5 GHz \\  & Reception & 12.250 GHz-12.750 GHz \\  & Transmission & \(\geq\)27 dBi \\ Antenna Gain & Reception & \(\geq\)27 dBi \\ Antenna main lobe beam width & Azimuth & \(\leq\)2.5\({}^{\circ}\) \\  & Pitch & \(\leq\)16.8\({}^{\circ}\) \\ First sidelobe & & \(\leq\)\(-\)11 dB \\ Polarization Type & & Linear polarization \\ Polarization isolation (duplexer outlet) & Transmission & \(\geq\)19 dB \\  & Reception & \(\geq\)19 dB \\ Insertion loss of transmission branch & & \(\leq\)1.5 dB \\ (excluding radome) & & \(\geq\)200 W \\ Port power capacity & & \(\geq\)95 dB \\ Transmission and reception isolation & & \(\pm\)270\({}^{\circ}\) (continuous) \\ Antenna motion range & Pitch & 20\({}^{\circ}\)-80\({}^{\circ}\) \\ Polarization surface adjustment range & & \(\pm\)90\({}^{\circ}\) \\  & Azimuth & \(\geq\)60\({}^{\circ}\)/s \\ Maximum rotation speed of antenna & Pitch & \(\geq\)60\({}^{\circ}\)/s \\  & Polarization & \(\geq\)30\({}^{\circ}\)/s \\ Tracking method & & Automatic tracking \\ Tracking Accuracy & & \(\leq\)0.3\({}^{\circ}\) (R.M.S) \\ Star capture time & & \(\leq\)10 s \\ Recapture time & & \(\leq\)6 s \\ Weight & & \(\leq\)27 kg \\ Reference source frequency stability & & \(2\times 10^{-8}\) \\ Working temperature & & \(-\)40 \({}^{\circ}\)C-60 \({}^{\circ}\)C \\ Storage temperature & & \(-\)55 \({}^{\circ}\)C-70 \({}^{\circ}\)C \\ Working humidity & & \(\leq\)95\% (+30 \({}^{\circ}\)C) \\ Standards for impact vibration & & GJ8367A [(48)] \\ \hline \hline \end{tabular}
\end{table}
Table 2: Technical indicators of the mobile communication equipment.  
the overlap area of the two frames of images is not less than 1/4, the coverage distance of each frame of image in the flight direction is 111 m. The corresponding field of view (FOV) angle and stability accuracy threshold can be expressed using the following formulas:  
\[\alpha_{targ}=tg^{-1}(a/L) \tag{1}\]  
\[\beta=\frac{1}{4}\alpha_{targ} \tag{2}\]  
Among them, \(a\) is the coverage distance, \(L\) is the target distance, \(\alpha_{targ}\) is the FOV angle, and \(\beta\) is the stable accuracy threshold. The stable accuracy calculation principle is shown in Figure 2. When the coverage distance is 111 m and the target distance is 3000 m, the FOV angle is 2.12\({}^{\circ}\). Therefore, if the stable accuracy is less than 0.530\({}^{\circ}\), the image stitching is effective.