## 3 CapsNet-GA Method for Electromagnetic Characteristic Fitting
### Select the Optimized Design Variables  
There is a wide variety of aircraft types, both at home and abroad, with diverse shapes. Their Radar Cross Section (RCS) spatial distribution characteristics cannot be exactly the same, but they generally share some similar features. Taking a certain type of American aircraft as a typical example, its RCS spatial distribution characteristics [24] are shown in Figure 5. The data are sourced from the article publicly published by [PERSON] of the Hellenic Air Force in Springer magazine in January 2018. It can be seen from Figure 5 that the main characteristics of the RCS distribution in the direction of the aircraft nose are as follows: Firstly, there are distinct RCS peaks within relatively narrow airspace ranges at several angles. Secondly, within a broader airspace range, there are lower (compared to the aforementioned peaks) RCS values with certain fluctuations. On the other hand, due to the complex structure of aircraft, there exist multiple scattering centers. Therefore, to achieve accurate simulation, it is mainly sufficient to accurately simulate the several abovementioned characteristics. In addition, an obvious peak appears at the \(0^{\circ}\) position, with the RCS value being 26.88 dBm. This is mainly contributed to by the strong scattering parts, such as the cockpit and the inlet duct at the nose. The angle between the points where the peak at the \(0^{\circ}\) direction drops by 3 dB on both sides is 2 degrees. Two secondary high RCS peaks occur near \(-7^{\circ}\) and \(7^{\circ}\), with their RCS values being 10.28 dBm and 9.10 dBm, respectively. These are mainly contributed by the strong scattering parts, such as the nose-mounted equipment and the leading edge of the wing. The next RCS peaks appear at \(-9^{\circ}\) and \(9^{\circ}\), with the RCS values being 8.91 dBm and 8.87 dBm, respectively. These peaks can be  
Figure 5: The RCS distribution characteristic. accurately simulated by using a 60\({}^{\circ}\) corner reflector. Secondly, the average RCS value in other spatial angle ranges is around \(-5\) dBsm and has certain fluctuations, which can be accurately simulated by using a Luneberg lens. When the signal-to-noise ratio (SNR) is 12.5 dB and the false alarm probability \(\mathrm{P_{fa}}\) is \(10^{-3}\), the detection probability \(\mathrm{P_{d}}\) is 0.995. When the SNR is 11.5 dB and the false alarm probability \(\mathrm{P_{fa}}\) is \(10^{-3}\), the detection probability \(\mathrm{P_{d}}\) is 0.95. In this paper, the minimum tolerable target detection probability is set to 0.95, and it can preferably reach 0.99. Then, it can be calculated that the SNR error should not exceed \(12.5-11.5=1\) dB. Therefore, the accuracy error of electromagnetic characteristic simulation is required to be no more than 1 dB. Based on the RCS distribution characteristic shown in Figure 5, in order to achieve the accurate fitting of electromagnetic characteristics, the parameter model of electromagnetic characteristic fitting is designed as shown in Figure 6.  
The parameter model of electromagnetic characteristic fitting shown in Figure 6 is mainly composed of one large-sized 60\({}^{\circ}\) corner reflector, one pair of small-sized 60\({}^{\circ}\) corner reflectors, and one pair of Luneberg spheres. The specific size and spatial distribution are the optimization target parameters of electromagnetic characteristic fitting that need to be given in the research design, and thus the optimization design and optimization method of electromagnetic parameter fitting are obtained. The main process parameter optimization variables that have a greater impact on the surface quality are the right-angle side length \(a\) of the large-angle reflector of the main scatterer, the right-angle side length \(b\) of the small-angle reflector of the secondary scatterer, the diameter \(c\) of the Luneberg sphere of the secondary scatterer, the relative position \(d_{1}\) of the Luneberg sphere, and the relative position \(d_{2}\) of the small-angle reflector.