Electromagnetic Modeling And Interactive Computation Of Equivalent Circuit-field Distribution Conversion For The Frequency Selective Surface Microwave Absorber

The demand for electromagnetic stealth technology is increasingly urgent with the continuous development of electromagnetic detection technology in modern wars.The Frequency Selective Surface(FSS)absorber plays an important role due to its unique absorbing characteristics.In this thesis,the relationship between the electromagnetic pattern model parameters and the circuit parameters are acquired,based on the equivalent circuitfield distribution interactive calculation theory.And then,a modeling calculation method from field distribution to equivalent circuit about the square loop and crossed dipoles frequency selective surface absorber are established,which are combined with the asymptote fitting method for the ohmic loss.Furthermore,the Particle Swarm Optimization(PSO)algorithm is adopted to achieve the transformation of parameters from equivalent circuit to field distribution.Modeling calculation method from field distribution to the equivalent circuit and design method from equivalent circuit to field distribution are integrated to obtain an electromagnetic model that satisfies the target's absorbing performance.Finally,both the single-layer active absorbers and the double-layer passive absorber are designed to achieve wide-band absorption.In this thesis,the square loop frequency selection surface is electromagnetically modeled,and its structure dimension parameters are extracted.Subsequently,the equivalent circuit parameters are obtained by using the equivalent circuit-field distribution conversion model.And then,the transmission line theory is adopted to calculate the frequency response of the microwave absorber,which achievers better matching compared with the full-wave simulation results.By investigating the dispersion characteristics of the inductor and capacitor of the equivalent circuit of square loop pattern,the influence of the pattern topology parameters,relative dielectric constant of the dielectric substrate,and thickness of dielectric substrate on the inductance and capacitance of the equivalent circuit with frequency can be obtained,the reliability of the equivalent circuit-field distribution conversion model calculation theory is verified further.Then the asymptotic model is used to fit the ohmic loss of the single square loop FSS absorber with resistance-loaded,which calculates the frequency and absorbing bandwidth together with the equivalent circuit-field distribution conversion interactive computing model.It is proved that this method can effectively predict the absorption performance of the absorber by comparing it with the full-wave simulation results.Afterwards the particle swarm optimization algorithm is used to quickly optimize the optimal envelope performance of the active square loop absorber,at the same time inverse best electromagnetic pattern model parameters.Correctness is verified in the HFSS software against inversion structure.Lastly,the absorber with the reflectance of less than-10 d B in the range of 2.3 GHz to 14 GHz is realized by using this design approach.Based on the analysis of the single square loop,the crossed dipoles pattern is further introduced,and by using the above method,the absorbing property of the crossed dipoles pattern FSS absorber is effectively predicted.In order to improve the absorbing bandwidth,a double-layer absorber consisted of a single square loop pattern and a crossed dipoles pattern is established,and the multi-layer modelling formula is used for fitting verification.Combining with the particle swarm optimization algorithm to optimize the multi-layer absorber quickly and efficiently,the double-layer absorber is prepared by experiment and the-10 d B broadband absorption from 1.35 GHz to 11.5 GHz is realized.