Research On Mechanism Analysis And Design Of Periodic Leaky-wave Antennas Based On Electromagnetically Complementary Structures

Leaky-wave antennas(LWAs)are a type of travelling wave antennas constructed from transmission lines(TLs)with continuously or periodically distributed radiation elements.LWAs feature compact geometry structure,high directivity,and unique frequency beam scanning,and hence are found promising in many wireless systems such as radar.With continuously increasing demand for wireless systems,research on LWAs focusing on function enhancement and enrichment has been an important branch of antenna engineering.Limited by the electromagnetic properties of the radiation elements,the reported LWAs have inherent defects,such as limited beam scanning range,stopbands,unstable gain,high side lobe level,low front-to-back ratio,and so on.Therefore,in this dissertation,efforts are made on review,mechanism analysis,and conceiving of radiation elements of LWAs,based on which an LWA design concept of utilizing electromagnetically complementary structures to design periodic LWAs is proposed to avoid the inherent defects of traditional LWAs,aiming for the application extension of LWAs and performance improvement of systems deploying LWAs.This dissertation is composed of four main parts as follows.First,equivalent circuit analysis of periodic LWAs is applied for understanding the basic radiation and stopband preoperties of periodic LWAs from a straightforward point of view,which lays the research foundation of this dissertation;and equivalent circuit analysis is also used to theoretically analyze the working mechanism of LWAs with reflection canceling structure,making design procedure of this type of LWAs explicit and efficient.Moreover,the equivalence between periodic LWAs and lossy TLs is pointed out and is utlized to develop a “black box” method which can be applied for geometry parameter value determination in LWA designs.The proposed “black box” method is avaible for LWA with complex geometry structure,as only external impedance parameters of the LWA unit cell need to be observed and adjusted,regardless of the precise electromagnetic properties of specific components.This part of the dissertation strongly support the succeeding researches by providing fast and effective method for geometry parameter value determination of periodic LWAs.Second,an LWA design method based on complementary reactance loading is proposed to suppress OSB through flexible impedance matching,aiming for the realization of continuous beam scanning of a periodic LWA through broadside.The complementary reactance loading is not only feasible to design linearly polarized periodic LWA but also circularly polarized periodic LWA.Furthermore,it is pointed out that the circularly polarized beam scanning range of a periodic LWA can be maximized as the radiation components of othogonal polarizations keep consistant radiation patterns over a bandwidth as large as possible.The resulted designed periodic LWA features larger circularly polarized beam scanning over most of the peer designs.Third,the essential reason of gain fluctuation regarding frequency in LWAs is clearly found out,and hence we propose to design periodic LWAs with radiation elements with not only complementary reactances but also complementary radiation performances with respect to frequency.The designed periodic LWAs present constant radiation efficiency and realized gain over the entire frequency band where beam scans continuously from backward through broadside to forward.Furthermore,thanks to the unique structure topology,periodic LWAs with complementary radiation performaces show easier aperture synthesis than traditional LWAs,and hence several prototypes are designed with typical aperture distributions which achieves precise side lobe leve control.Last but not least,inspired by abovementioned design methods where radiation elements with complementary components are applied and in fact form new resonance in LWAs,we propose to further utilize complementary resonant structures in periodic LWA design seeking more design potential.Magneto-electric(ME)dipole is then implemented as practical realization of complementary resonant structure,resulting in two types of periodic LWAs.One periodic LWA achieves constant high radiation efficiency,stable gain,and high front-to-back ratio,which benefit from the broadband property of complementary resonant structure and the unique radiation properties of ME dipole.The other periodic LWA takes advantage of the flexible frequency responses of impedance and phase delay of the complementary resonant structure,and obtains broadband fixed beam,which is abnormal and hard to realized for tradiational LWAs.The obtained broadband fixed beam means that such type of periodic LWA is promising in the future broadband wireless communication systems.Aiming for sovling practical problems of LWAs,the research in this dissertation is guided by equivalent circuit model analysis,adopts design methods combining theory derivation and numerical simulation,and presents several periodic LWAs with unique properties,which are verified by experiments.Some of the design concepts proposed in this dissertation are universal for periodic LWAs with variety of kinds of TLs and radiation elements.This dissertation gradually reveals and solves the inherent defects of traditional LWAs.The contents of dissertation are the prelude of the research of new generation of periodic LWAs,and firmly support the enhancement and update of morden wireless systems.