| Frequency-selective surfaces are infinite periodic array structures that possess selective and manipulated characteristics concerning the frequency,amplitude,phase,and polarization of spatial electromagnetic waves.Therefore,they find extensive applications in the design of electromagnetic devices or components such as antenna radomes,sub-reflectors,polarization rotators/converters,and circuit analog/frequency-selective absorbers.Traditional frequency-selective surfaces are typically composed of planar single or multilayered metal or aperture unit cell(element)structures in a twodimensional periodic arrangement.However,the element structure,analysis methods,and design theories of traditional frequency-selective surfaces have suffered from several limitations:(i)They can only manipulate spatial electromagnetic waves in two-dimension directions,thus limiting the achievable performance and manipulation capabilities.(ii)They rely on classical(quasi-)lumped circuit analysis and design methods,resulting in low analysis accuracy and design efficiency.(iii)Their design freedom is constrained,leading to limited achievable manipulation performance of electromagnetic wave.In view of these challenges,this dissertation takes a novel approach and focuses on the study of a new type of frequency-selective structure(FSS)to overcome the technical bottlenecks limiting the control capabilities of traditional two-dimensional frequency-selective surfaces,and to address the inefficiency and lack of generality in existing synthesis design methods.This research aims to establish a research framework encompassing novel FSS modeling and analysis methods,synthesis design theories,and integrated functional applications.The ultimate goal is to fundamentally enhance the means of manipulating electromagnetic waves and achieve high-performance outcomes.The main contributions of this dissertation are summarized as follows:(1)Modeling and analysis of guided wave-based FSS using stacked slotline elementThis dissertation proposes a modeling approach for guided wave-based FSS using stacked slotline element.Through the introduction of the “Short-Open-Load(SOL)” calibration technique and the utilization of the “field-circuit” combination approach,the working mechanism of the guided wavebased element and the extraction procedure of the general equivalent circuit parameters are systematically investigated.The research results demonstrate that the guided wave-based element not only efficiently facilitates the conversion between spatial electromagnetic waves and guided waves but also exhibits advantages such as wideband single-mode(quasi-TEM mode)transmission,compact unit cell size,and integrated processing.Moreover,this marks the first application of the SOL calibration technique for precise extraction of equivalent circuit parameters in FSSs,thereby establishing a foundation for the synthesis design of high-performance guided wave-based FSSs.(2)Synthesis design of bandpass FSSs based on resonator loadingBuilding upon the guided wave-based FSS using stacked slotline element,this research extends and applies the synthesis theory of planar microwave filters to the analysis and design of guided wave-based FSSs.Guided by the synthesis theory of N-order bandpass filter networks with resonator loading,a systematic design methodology is developed,bridging the gap between design requirements,filter network parameters,and the physical structure of guided wave-based FSSs,through the core analysis tool of the SOL parameter extraction method.Ultimately,a series of high-order narrowband bandpass FSSs are successfully designed and verified with characteristics such as stable operation under oblique incidence,multiple out-of-band transmission zeros,low profile,and dual polarization.This work contributes to the advancement of the theoretical analysis and synthesis design methods for frequency-selective surfaces/structures.(3)Synthesis design of transmissive wideband circular polarizersTaking advantage of the polarization separation design concept and the independent design capabilities of guide wave-based FSSs in orthogonal directions,an integrated design approach is established for simultaneous manipulation of amplitude,phase,and polarization.This work combines the synthesis theory of wideband bandpass filters and phase shifters to derive calculation formulas for axial ratio bandwidth and 90° phase deviation function.The general design principles for transmissive wideband circular polarizers with specified axial ratio bandwidth are proposed using the design of arbitrary adjacent order(N and N+1 order)wideband filters as a guideline.This offers new insights into the integrated manipulation of amplitude,phase,and polarization of spatial electromagnetic waves.(4)Synthesis design of function-integrated reflective arraysBy analyzing the inverse conditions of loading quasi-lumped inductive and capacitive structures within the stacked slotline element,a synthesis design methodology is proposed to achieve 90° polarization rotation and reflection manipulation of incident spatial electromagnetic waves.Furthermore,through the analysis of phase conditions for hybrid inductive and capacitive loading,a wide phase coverage range of guided wave-based FSS element is achieved.Building upon this,the design principles for precise manipulation of the reflected beam under linear polarized incidence of planar electromagnetic waves are explored by integrating the design theories of antenna arrays and approximate design methods for quasi-periodic arrays,leading to the realization of single-beam and dual-beam steering functionalities.The results demonstrate that through a systematic and integrated design of guided wave-based FSS elements,efficient and precise manipulation of spatial electromagnetic wave at amplitude,phase,polarization,and beam steering characteristics can be achieved. |
