## 3 CapsNet-GA Method for Electromagnetic Characteristic Fitting
### Construct Optimization Objective Function  
To carry out the optimization of the RCS distribution characteristics of the radar target drone combination, it is first necessary to select the parameters with greater influence as the focus of the optimized design. In the practical application of the radar target drone combination, there are various scatterers. The size of the main scatterer, the size of the secondary scatterer, and the relative position between the scatterers are the basic elements of the structure of the radar target drone combination. Therefore, these parameters are selected in this chapter to optimize the design of the radar target drone combination. Based on the flow of the genetic algorithm for electromagnetic parameter fitting optimization in Figure 1, the corresponding optimization design model is established. The minimum value of the optimization objective function of electromagnetic parameter fitting optimization can be solved through Equations (6) and (7), and the optimal solution of the optimization variable can be obtained. However, the changes in the size and relative position of each target in the electromagnetic parameter fitting optimization affect the RCS peak error, the angle error corresponding to the RCS peak point, and the RCS average error in the non-peak region. Therefore, based on this situation, we consider another setting of optimization variables. After determining the variables of electromagnetic parameter fitting optimization, a corresponding RCS distribution characteristic can be obtained through simulation analysis by FEKO. In this paper, FEKO 2019 is applied to calculate the far-field RCS distribution characteristics of the target. FEKO is a software program for electromagnetic calculation and electromagnetic field analysis, which is widely used in electromagnetic scattering simulation. FEKO has numerous solvers, and the solvers can be selected according to specific simulation requirements. FEKO integrates many methods of electromagnetic numerical calculation, including the Method of Moments (MOM), the Fast Multipole Method (MLFMM), and the Ray Tracing Geometrical Optics Method (RL-GO). In this paper, the algorithm based on the improved capsule network and genetic optimization is imported into the FEKO software to generate a solver, through which the precisely simulated model and its optimal solution can be obtained. To solve the distribution characteristics of the Radar Cross Section (RCS) using FEKO, it is necessary to first establish a model. CADFEKO has the function of creating geometric models. After the model is built, it can be imported into FEKO. Then, relevant parameters, such as setting the incident wave frequency to 10 GHz and the scanning angle from \(-30^{\circ}\) to \(30^{\circ}\), and the monostatic working mode, should be configured. Subsequently, a far-field RCS scan is carried out, and the RCS values corresponding to each angle can be obtained. Finally, the RCS distribution characteristic curve within the range of \(-30^{\circ}\) to \(30^{\circ}\)is generated, as shown in Figure 5. Then, compare the error magnitudes of \(x_{1}\), \(x_{2}\), and \(x_{3}\), respectively. The smaller the error, the closer the value of the optimization variable is to the real value. The optimization objective function \(g\) is set as:  
\[g(a,b,c,d_{1},d_{2})=\left|x_{1}-{x_{1}}^{\prime}\right|+\left|x_{2}-{x_{2}}^{ \prime}\right|+\ldots+\left|x_{m}-{x_{m}}^{\prime}\right| \tag{8}\]  
where \(x_{1}\) represents the peak error of parameter \(a\), \(x_{2}\) denotes the angular error corresponding to the peak of parameter \(a\), \(\ldots\) and \(x_{m}\) indicates the average error in the non-peak region of parameter \(d_{2}\). The closer the objective function is to zero, the closer the RCS distribution characteristic of electromagnetic parameter fitting optimization is to the fitted electromagnetic characteristic.