| Frequency selective surface(FSS)is an artificial electromagnetic periodic structure,exhibiting desirable frequency responses.FSS could be opaque or transparent for particular frequency of interest.It has low reflection/transmission loss in operation band,its bandwidth and resonant frequency also could be tuned easily.Thus,many researchers have paid much attention to FSS continuously since it was invented.Although there are many literatures reported on this topic,most of them are focused on the investigations of shape of single layer FSS and the methods for miniaturization.However,the multi-layered FSSs,which are significantly valuable for engineering applications,are less discussed in previous researches.Moreover,some emerging applications with more strict requirements on FSS are to be studied,such as bandpass FSS with ultra-wide band reflection properties,circular polarization(CP)FSS,and etc.According to previous investigations and new requirements on FSS,this dissertation is dedicated to realize bandpass FSS with ultra-wide band rejection properties and CP FSS.FSS structure,working principles and design methods are deeply analyzed using equivalent circuit model(ECM).The contents of this dissertation are given briefly as follows:First of all,the background and research prospect of FSS are introduced.Research dynamic at home and abroad are sorted out by their applications.Furthermore,the working principles of several FSSs in great demand are analyzed,their advantages and drawbacks are also summarized,which provide a reference and comparison to our work.Then,the disadvantages of traditional resonant FSS on the design with wideband rejection properties are presented.Novel cascaded structure composed by non-resonant elements are employed to address this issue.This cascaded structure contains capacitive layers and inductive layers,which are arranged one by one and separated by dielectric slabs with proper thickness and permittivity.A bandpass FSS exhibiting ultra-wide stopband is achieved using this proposal.In addition,array interference phenomenon in the cascaded structure is studied based on Smith Chart,and it is suppressed by an effective method presented in this thesis.Simulated results indicates that,the designed FSS has excellent performances,like low insertion loss in passband,high rectangle coefficient of filter response and wideband rejection behaviors.Next,for the design of CP FSS working in K band,square slot is selected as metallic pattern in unit cell.Theoretical analyses of response consistency between TE and TM waves with respect to incident angle and FSS geometrical dimensions are presented,which is a ground stone for multi-layered FSS design.Then,a dual layer square slot FSS is used and its performances are optimized through ECM.In final results,the insertion loss and axial ratio of CP wave both are less than 1dB in passband for incident angle ranging from 0° to 60°.Moreover,the optimized dual layer square slot FSS are fabricated and tested,a good agreement between simulated and measured results is obtained,which validates our analyses and design methods.Finally,the FSS mentioned in Chapter 3 is redesigned to operate at CP wave in passband.The original wire inductive layer is replaced by spiral meander line(SML),inductive effect increases within a limited unit cell size.As a result,response consistencies between TE and TM waves are improved by using SML.Moreover,Good behaviors of CP wave transmission in L/S band and a wide rejection band from 5 to 25 GHz are achieved through optimization utilizing ECM. |
