Investigation On Scattering Characteristcs Of Left-handed Dielectric Periodic Structures

Dielectric periodic structures(DPSs) have been widely used in electromagnetic areas owing to their advantages like low loss,low material requirement,easy to be integrated and fabricated.Left-handed gratings(dielectric periodic structures composed of left-handed materials) have their own unique merits compared with the traditional DPSs because of the particular properties of left-handed materials.The scattering problems of DPSs are always important topics in electromagnetic areas. With the thorough analysis of left-handed gratings,kinds of merits of left-handed gratings gradually emerged,and also many unique electromagnetic scattering characteristics.In present dissertation,the scattering characteristics of left-handed gratings are systemically analyzed by a method which combines the multimode network theory with the rigorous mode matching method.Comparisons for the scattering properties between left-handed gratings and right-handed gratings are given and their new phenomena and applications in electromagnetic areas are also revealed.The scattering characteristics of rectangle and arbitrary profiles left-handed gratings,left-handed periodic arrays with plane-wave principle-plane incidence are carefully analyzed.The effects of structure parameters,dielectric loss,periodic groove profiles and the number of periodic layers on the scattering characteristics of left-handed gratings and also the effects of left-handed uniform layers on the frequency selective characteristics of traditional dielectric gratings are presented in details.And comparisons of scattering properties between the left-handed and traditional right-handed gratings are also shown with some explanations to the electromagnetic scattering phenomena.It is indicated that much larger total reflection bandwidth and more maximum refletions can be achieved with left-handed gratings compared with right-handed gratings.Diametrically opposited scattering propeties can be achieved by modified left-handed and right-handed characteristics,respectively.After that,scattering and complete polarization conversion characteristics of left-handed gratings at plane-wave three dimensions(3-D) incidence are carefully analyzed using multimode network theory and the rigorous mode matching method combining with the coordinate rotating theory.The effects of structure parameters, dielectric loss,and the 3-D incident angles on the scattering characteristics of left-handed gratings are studied in details.It is indicated that the incident angles have great effects to the reflection characteristics of left-handed gratings which obviously different from the situation of right-handed gratings.Further more,the coupling between modes are even more evident in left-handed gratings with plane-wave 3-D incidence compared with right-handed gratings,which make left-handed gratings can realize complete polarization conversion between TE and TM modes in a much larger frequency region,while this property can hardly realize in the traditional right-handed gratings.Comparisons of polarization conversion properties between right-handed gratings and left-handed gratings are given with detailed physical explanations in the present dissertation.Electromagnetic wave absorbing characteristics of left-handed uniform layers and left-handed gratings are also given at the end parts of the dissertation.Applications of left-handed graings in electromagnetic absorbers are explored.New double-layered electromagnetic absorbers are also presented.These new absorbers have great power attenuation in large frequency bands with simple structure and minimal thickness. These results are of reference significance guidelines for the design of new electromagnetic absorbers and of practical prospects for stealth technology.The investigations of scattering characteristics about left-handed gratings in present dissertation provide important theoretical guidelines for the design of new frequency selective surfaces,couplers,filters,polarization convertors and electromagnetic absorbers for microwave and millimeter wave applications.