# Intelligent Simulation Technology Based on RCS Imaging
## 2 Target Drone Simulation Principle  
### Variable Principle of Corner Reflector  
The RCS of the target is used to represent the intensity of the signal reflected back to the radar receiver after the radar transmitter emits an electromagnetic wave towards the surface of the target. It is a physical quantity indicating the scattering ability of the target scatterer to the radar transmitted wave. It is defined as 4\(\pi\) times the ratio of the power scattered by the target in the receiving direction and the plane wave power density incident at the target from a given direction in a unit solid angle. It is denoted by \(\sigma\), and can be expressed as follows:  
\[\sigma=\lim_{R\rightarrow\infty}4\pi R^{2}\frac{S_{r}}{S_{i}}=\lim_{R \rightarrow\infty}4\pi R^{2}\frac{\left|E_{r}\right|^{2}}{\left|E_{i}\right|^ {2}}=\lim_{R\rightarrow\infty}4\pi R^{2}\frac{\left|\mathrm{H}_{r}\right|^{2} }{\left|\mathrm{H}_{i}\right|^{2}} \tag{1}\]  
where \(R\) represents the radar-target distance, and \(S_{r}\), \(E_{r}\) and \(\mathrm{H}_{r}\) represent the energy flow density, electric field strength, and magnetic field strength of the target echo signal received by the radar, respectively. The energy flow density, electric field strength, and magnetic field strength of the radar transmitting signals to the target are denoted by \(S_{i}\), \(E_{i}\) and \(\mathrm{H}_{i}\), respectively. The RCS value is scalar, measured in square meters. Its logarithmic representation is commonly used in practical applications, i.e., for the number of decibels per square meter (also known as decibel square meter, denoted as dBsm), and the expression is as follows:  
\[\sigma_{dBsm} =10\mathrm{lg}\sigma \tag{2}\]The variable RCS properties of corner reflectors can be further analyzed by considering the angle, frequency, polarization mode, and the number of reflections of the incident wave. Usually, electromagnetic calculation methods such as Geometrical Optics (GO), Area Projection (AP), and Physical Optics (PO) are used for analysis. The traditional GO algorithm can effectively calculate the RCS value of a trihedral corner reflector. However, as it is a high-frequency approximation method, it considers the electromagnetic wave as a beam with a wavelength of 0, which makes it impossible to analyze the polarization mode of the incident wave. The PO method cannot be further extended and applied to irregular corner reflectors with more complex structures due to its inability to calculate the irradiation area. Therefore, this article uses the PO-AP algorithm to analyze the omnidirectional RCS of the diagonal reflector model. Assuming that the metal flat plate forming the corner reflector is an ideal conductor, the reflecting object will induce twice the current \(2n\times H_{i}\) corresponding to the incident tangent magnetic field on its surface, where \(n\) is the normal vector of the reflector surface. The reflected magnetic field at the observation point, whose distance from the origin is \(r\), can be determined by the PO method as follows:  
\[H_{\rm s}=\frac{jk}{4\pi}\frac{\exp(-jkr)}{r}\int_{s^{\prime}}2(\hat{n}\times H _{i})\times\hat{r}\exp(jk\hat{r}\cdot r^{\prime})ds^{\prime} \tag{3}\]  
where \(H_{i}\) is the incident magnetic field that reaches the surface of the reflecting object, while \(\hat{r}\) and \(r^{\prime}\) are the unit and distance vectors from the incident point to the origin, respectively. Equation (4) integrates the area \(s^{\prime}\) where electromagnetic waves irradiate the reflector. The incident wave may be reflected zero to three times inside the corner reflector, and only three reflected echoes will return to the radar receiver along the path of the original incident direction. Thus, three reflections within a large angular range form the main contributing source of the corner reflector RCS, while up to two reflections can be ignored when calculating the monostatic RCS. The ability of the incident wave to be reflected three times depends on the mutual determination of the incident point P and the incident direction.