Synthesis Theory And Application Research Of Transmission-Line Type Three-Dimensional Frequency Selective Structures

Frequency selective surfaces are artificial electromagnetic array structures composed of several identical metallic,dielectric,or composite element arranged in a two-dimensional period,which have selective manipulation for spatial electromagnetic waves with different operating frequencies,polarization states and incidence angles.However,the conventional frequency selective surface only manipulates spatial electromagnetic waves in the two-dimensional periodic plane,severely restricting its performance and means.This dissertation systematically studies a class of transmission-line type three-dimensional(3D)frequency selective structure(FSS)and its synthesis design theory based on planar guided-wave structure,which greatly enriches the manipulation means,improves the design efficiency,and enhances the performance.Besides,this dissertation creates good conditions for its application in spatial-wave manipulating devices with various functions.The details of the research are as follows.1.Based on the waveguide equivalence method,network modeling and parameter extraction of the transmission-line type 3D FSS are studied,which provides a theoretical basis for the synthesis design of it.Firstly,based on Floquet’s theorem and image theory,the waveguide equivalence condition of the periodic structure in the case of normal incidence is derived.The analysis method of equivalent waveguide instead of periodic boundary condition is established,addressing the problem of low efficiency in solving traditional 3D FSS element.On this basis,the stacked slotline structure is used to construct the transmission-line type 3D FSS,and the network model of the element structure is established.By performing network analysis on its equivalent circuit,the exact mapping relationship between the element structure dimensions and the equivalent circuit parameters is established.The research results show that the transmission-line type 3D FSS can convert spatial waves into guided waves for manipulation,which greatly reduces the complexity of equivalent circuit modeling and effectively improves the accuracy of circuit parameter extraction.2.Based on the multimode resonance and the synthesis design theory of wideband filters,the synthesis design method of transmission-line type 3D FSS in manipulating magnitude of spatial waves is investigated.Then,two types of wideband 3D FSS,coupled transmission-line type and branch transmission-line type,are proposed.First,by loading the stacked slotline with steppedimpedance slotline and microstrip branch-line respectively,the construction of multimode resonator in the transmission-line type 3D FSS element is studied.On this basis,the equivalent circuit models of the above two types of transmission-line type 3D FSSs are established through a combined "field-circuit" analysis method.A general synthesis design method is proposed according to the relationship between Chebyshev function and its magnitude response.Simulated and experimental results show that both transmission-line type 3D FSSs have the advantages of wide bandwidth,high selectivity,and good angular stability.Moreover,they solve the problem that the 3D FSS is difficult to be efficiently synthesized.3.Based on the idea of polarization separation design,the synthesis and design methods of transmission-line type 3D FSS in manipulating phase of spatial waves are investigated.Then,two types of wideband linear-to-circular polarization converters,quasi-lumped element loaded transmission-line type and coupled transmission-line type,are proposed.First,to address the problem that the horizontal and the vertical paths of conventional linear-to-circular polarization converter are difficult to be manipulated independently,two paths of the polarization converter are modeled separately by employing the stacked slotline structure.Thus,quasi-lumped element loaded transmission-line type linear-to-circular polarization converter is designed,which achieves low loss,low axial ratio(AR)and wide bandwidth.Second,to address the problem that the wideband linearto-circular polarization converter is difficult to be synthesized,a coupled transmission-line type 3D FSS is used as the manipulation structure of the two paths.Meanwhile,the phase slope condition is introduced to expand the operating bandwidth.The relationship between the required AR and the design specifications of the two paths is even derived,which develops a sophisticated synthesis design theory.In addition,this type of polarization converter also has the advantages of low loss and good angular stability.4.Based on the design method of Jauman screen,the synthesis design method of transmissionline type 3D FSS in absorbing spatial waves is investigated.Then,a wideband microwave absorber based on transmission-line type 3D FSS is proposed.To address the problems that conventional microwave absorbers require optimized design due to discontinuities in permittivity of dielectric substrate and square resistance of resistive sheet,a wideband microwave absorber composed of multiple sections of uniform slotline type 3D FSS and surface-mounted resistors is proposed based on the design method of Jauman screen.With the high design freedom of stacked slotlines and surface-mounted resistors,a synthesis design method is developed,which greatly improves the design efficiency.Compared with the existing microwave absorbers,this transmission-line type 3D FSS based microwave absorber has the advantages of simple and efficient design method and good angular stability.Besides,it can adjust the absorption bandwidth and absorption rate by only changing the resistance value of the surface-mounted resistors.