Research On Broadband Frequency Selective Surface Based On Multi-objective Genetic Algorithm

As the modern communication system is developing in the direction of broadband and miniaturization,the novel frequency selective surface of broadband,ultrathin and wide-angle characteristics becomes a research hotspot and difficulty in the field of communication and microwave.Frequency selective surface can realize frequency selection of electromagnetic wave with different frequencies and polarization modes,so it is widely used in engineering and military fields,including radome,absorber,electromagnetic shielding,and radar cros s section reduction.After years of research and development,the design method and function of the FSS have been improved,but there are still problems with narrow bandwidth,large thickness and poor oblique incidence stability.In addition,multilayer structure is the mainstream solution to realize broadband,which leads to complex and time-consuming of the structure design,and easy to fall into the local optimal solution.In this paper,a multi-objective genetic algorithm based on the equivalent circuit model and equivalent medium theory is proposed to solve the above problems in the research on FSS.This algorithm is suitable for broadband frequency selective surface design and can quickly search for the global optimal solution.It provides a new method to break through the limitations of traditional manual selective FSS units and optimization of structure parameters.The research work of this paper is as follows:Firstly,the basic theory of broadband frequency selective surface is systematically discussed.Based on Floquet theory and grating lobe phenomenon,the equivalent circuit models of various frequency selective surface units are derived,which lays a theoretical analysis foundation for the subsequent design of broadband frequency selective surface using multi-objective genetic algorithm.Then,the mechanism of the perfect matching layer is studied,and the equivalent medium parameter conditions of perfect matching are derived,and the characterization and extraction methods are given,which provide theoretical guidance for exploring the novel broadband frequency selective surface design.Secondly,to solve problems of the narrow bandwidth and large thickness,and to solve the complex and time-consuming problem of multi-layer structure modeling,a multi-objective genetic algorithm for broadband transmission type FSS was proposed.To verify the effectiveness of the proposed method,a coupled type broadband passive FSS was designed.The transmission bandwidth was extended to7.2-14.6 GHz with a fractional bandwidth of 67.9% by using the second-order bandpass filter response and coupling effect.Then,in order to realize the reconfigurable function of the FSS structure,a broadband switch-type active frequency selective surface based on the modified equivalent circuit model of PIN diode is proposed,which realizes the switching between the “transmission” and“shielding” functions in X-band.The transmission bandwidth is 8.2-10.5GHz and the fractional bandwidth is 24.6%.The shielding bandwidth is 2-18 GHz,and the oblique incident angle can reach up to.Simulation and experimental results verify the effectiveness of the proposed MOGA method.Then,in order to solve the problem that the absorption type frequency selective surface is difficult to take into account the absorption bandwidth and thickness,and the modeling is complex and time-consuming,a multi-objective genetic algorithm for the absorption type FSS is proposed.To verify the effectiveness of this method,a broadband wide-angle absorber based on ITO resistive films is designed first.Its absorption bandwidth is up to 2-18 GHz,the fractional bandwidth is 160%,the thickness is only,and the oblique incident angle can reach up to.Then,in order to adapt to the transparent application environment,an optically transparent broadband absorber is designed.The absorption bandwidth can reach2-18 GHz,the transparency can reach 60%,the thickness is only,and the oblique incident angle can reach up to.Simulation and experimental results verify the effectiveness of the proposed method.Finally,in order to solve the problems of large thickness and poor oblique incidence stability of the absorption type FSS,a multilayer inhomogeneous medium structure based on magnetic material was proposed.By flexibly adjusting the equivalent medium parameters of the magnetic material,the high absorption of 95%was achieved.Firstly,a pyramidal structure constructed by a single type magnetic material is designed.The absorption bandwidth is 2-18 GHz,the fractional bandwidth is 160%,the absorption in band is up to 95%,the oblique incident angle can reach up to,and the thickness is only.Then,in order to reduce the complexity of the structure,a trustum type structure with absorption bandwidth of 1-18 GHz was designed,the fractional bandwidth was 179%,the oblique incident angle can reach up to,and the thickness was only,which verified the effectiveness of the design method.In summary,aiming at the problems of narrow bandwidth,large thickness and poor oblique incidence stability existing in the current research on frequency selective surface,this paper closely combines theoretical research,model design,simulation and experimental verification,from the construction of equivalent circuit model,to the proposal of multi-objective genetic algorithm,to the design and implementation of FSS structure,and carries out a series of research and experimental verification work.A complete,efficient and accurate design method for broadband FSS structure design is proposed,which provides a solid theoretical basis and application guidance for its potential applications.