Design And Validation Of Frequency Selective Surfaces For Wave Transmitting And Stealth Performance

The frequency selective surface is a periodic array structure with selective performance for electromagnetic waves.Its excellent and flexible filtering characteristics make it have broad application prospects in the field of aircraft stealth design.As the application platform develops towards high frequency,high performance and complex surface,the impact of random factors such as manufacturing tolerance,assembly error and surface projection error cannot be ignored.However,traditional design methods focus on the implementation of planar cell performance,which cannot guarantee the stability and the consistency of performance of surface arrays with uncertainties.Therefore,a comprehensive design method considering robust optimization for planar FSS and curved FSS is presented and validated.This thesis is organized as follows:（1）The correction of the equivalent circuit was completed.Firstly,the equivalent circuit model of FSS was established,and the resonance analysis of the unit was completed.Then,the field correction factor and coupling correction factor were introduced to correct the equivalent circuit model to make it have more accurate frequency response.Finally,a series-parallel correction equivalent circuit of the deforming unit was constructed to describe the frequency response of the deforming unit.It lays a foundation for the establishment of the robust optimization surrogate model based on the modified equivalent circuit,the resonance analysis of the FSS,and the analysis of the deformation compensation of the FSS.（2）A robust optimal design method for FSS was presented.Firstly,the uncertainty factors of FSS were analyzed.There are two cases:the error interval is known and the error interval is unknown.And two types of robust optimization models were established respectively,where interval transformations are made.Then,the prediction result of the frequency response within the parameter range was used to establish the FSS robust target surrogate model based on the corrected equivalent circuit model.Finally,the FSS parallel robust optimization algorithm was formed.Taking the square ring slot element as an example,the deviation of the passband center frequency reduced by 0.15GHz and S₂₁ increased by 0.07d B,which verifies the effectiveness of the FSS robust optimization design method.（3）The design and validation of planar FSS were completed.Firstly,the equivalent circuit model was established and the resonance analysis was performed to determine the initial structure of the unit.Then,the parameters of the element was refined through robust optimization design.After the robust optimization,the S11 response within the parameter deviation range is more stable,and the overall downward movement is about 4d B.The experimental validation shows that the sample has a passband where transmittance is greater than 85%（S21>-0.7d B）in the range of 2.8GHz-3.2GHz.In the meanwhile,it has an absorbing band where absorbance is greater than 90%（S11<-10d B）in the range of 8.6GHz-11.7GHz.They are basically consistent with the simulation results.（4）The design and validation of surface FSS were completed.Firstly,two types of surface projection array methods were proposed.Then,a bandpass curved FSS was designed,according to the robust optimization method and surface projection array method.The experimental validation shows that the sample has a pass band where transmittance is greater than 85%in the range of 2.8GHz-3.1GHz.In the meanwhile,the reduction of RCS is greater than 15d B in X-band.It verifies the validity of the design method in this thesis.