Research On The Design And Characteristics Of High-performance Three-dimensional Frequency Selection Surface

Recently,frequency selective surfaces(FSSs),acting as spatial filters,are widely used in radar antenna radomes,antenna sub-reflectors,absorbers,electromagnetic shields,and so on.More and more researchers pay attention to the FSSs for their unique filtering characteristics.Compared with two-dimensional FSSs,three-dimensional(3D)FSSs have greater design freedom.Multiple resonant modes can be constructed in the unit cell,introducing multiple transmission zeros/poles,thus the performance of FSS is improved.In this article,we propose three types of three-dimensional unit cells,and design a series of 3D FSS with the advantages of dual polarizations,high selectivity,good angular stability and small electrical size.The detailed research contents are as follows:1.A novel three-dimensional unit cell is proposed,which consists of a cuboid dielectric block with two identical resonant elements and a square waveguide.By the electromagnetic coupling between the resonant elements,the original single resonant mode will split into even-or odd-resonant modes,resulting in multiple transmission zeros/poles.Hence,a series of 3D FSS with high performance are designed.The bandpass 3D FSSs with wideband,quasi-elliptic response,small band ratio dual-band,as well as highly-selective tri-band characteristics are realized by loading the square patch,square loop,double square loops and three square loops on the upper and lower end of the dielectric block,respectively.A third-order bandpass 3D FSS and a multilayer complementary tri-band bandpass 3D FSS are achieved by loading a concentric square loop in the middle layer.The operating principle of the proposed FSSs is explained by the equivalent circuit model,and the influence of structural parameters on the performance of FSS is studied.Finally,the prototypes of quasi-elliptic response bandpass FSS,three-order bandpass FSS,and small band ratio dual-band bandpass FSS are fabricated,assembled and measured.2.A novel three-dimensional unit cell composed of improved square coaxial waveguide(SCW)path and parallel-plate waveguide(PPW)path is proposed.Firstly,the evolution of novel unit cell is analyzed,and a bandpass 3D FSS with the quasi-elliptic response is designed and simulated.The electric field vector distributions at the frequencies of the transmission zeros/poles are given for explaining its operating principle.Secondly,on the basis of the proposed unit cell,a dual-band bandpass 3D FSS is proposed and simulated by loading the metallized holes in the middle of the PPW path,and its working principle is analyzed by the electric field vector distribution at the frequencies of the transmission zeros/poles.In addition,with the aid of multi-layer nested design idea,a dual-band bandpass 3D FSS with small band ratio is presented by nesting an improved SCW path in the proposed unit cell.The working principle is explained by the electric field vector distribution and equivalent circuit model.At the meantime,the influence of structural parameters on the resonant frequency is studied.Finally,the prototype of this FSS is fabricated and measured.3.A novel three-dimensional unit cell composed of split square coaxial waveguide(SSCW)path and PPW path is proposed.Firstly,the characteristics of SSCW path are investigated,and a bandpass 3D FSS with both-sided fast roll-off is designed based on the proposed unit cell.The working principle is explained by the electric field vector distribution.Meanwhile,the influence of structural parameters on the performance of FSS is researched.At last,the prototype of this FSS is fabricated and measured.Secondly,with the aid of multi-layer nested design idea,a dual-band bandpass 3D FSS with high selectivity is achieved by loading an SSCW path in the proposed unit cell.The electric field vector distribution at the frequencies of the transmission zeros/poles is analyzed for explaining the working principle.The influence of structural parameters on the performance of FSS is provided.In addition,a highly-selective tri-band bandpass 3D FSS is realized by nesting two SSCW paths in the proposed unit cell,and the electric field vector distribution at the frequencies of the transmission zeros/poles introduced by the inner SSCW path is investigated.