Research On Flexible Elliptical Leaky Waveguide

With the rapid development of our society,railway construction continues to extend to the midwest regions of our country.The stable and reliable railway mobile communication is an important guarantee for the safe operation of trains and the external contact of passengers,and the radio wave coverage system along the railway is the basis of railway mobile communication.Therefore,how to achieve efficient radio coverage of the system is still a research hotspot.Leakage waveguide is a kind of reliable radio wave covering method in that environment,which has the advantages of simple structure,convenient installation and low transmission loss.The elliptical leakage waveguide is more suitable for railway mobile communication system because of its flexible structure,which has the advantages of continuous long-distance processing,fewer joints in application,and more convenient in transportation and laying.The purpose of this paper is to find more practical waveguide structure parameters and provide a method to realize efficient,stable and reliable radio wave coverage in railway wireless communication environment.The main research work and innovative achievements of this paper are as follows:1.The structure of the elliptic leakage waveguide that works in the 5.8 GHz band is studied.By comparing the propagation constant that calculated by theory or the full-wave simulation software,it is proved that the elliptic waveguide theory can be used to guide the design of the leaky elliptic waveguide.The effects of different elliptic leakage waveguides that with different elliptic eccentricity on their transmission and radiation characteristics are studied.The results show that the cutoff frequency of the fundamental mode and near field distribution are mainly affected by the long axis of the ellipse of the waveguide,and the bandwidth of the main mode is mainly affected by the eccentricity of the cross-section ellipse of the waveguide.2.This paper proposes a circumferential directional leaky elliptical waveguide structure that with two rows of slots that symmetrically distributed with the center axis of the waveguide.Under the condition that the slots deviates from the center axis of the waveguide by different distance,the circumferential normalized electric field distribution of the waveguide that calculated by the he equivalent electromagnetic current integral approach and full-wave simulation analysis method are used.By comparing and analyzing the results of the two methods,we can conclude that when the slots deviate from the centerline,the beam width of the circumferential electric field pattern decreases,which means the circumferential directivity of the waveguide increases.In addition,the feeding structure of the elliptical waveguide is also studied,and the actual fabrication and measurement of the elliptical waveguide are carried out.It is verified that the structure can effectively concentrate the circumferential energy directly above the waveguide.3.In view of the problem that elliptical leakage waveguide is easy to bend and deform under the influence of external force,the elliptical leakage waveguide structure filled with dielectric is proposed.The radiation mode of elliptical leakage waveguide,the radiation field of single or multiple harmonics,and the circumferential directional dielectric elliptical leakage waveguide are studied when the dielectric is with different dielectric constants.An elliptical leakage waveguide filled with H-shaped dielectric or I-shaped dielectric is proposed.The attenuation constants of the elliptical leakage waveguide filled with H-shaped dielectric and I-shaped dielectric are analyzed and compared.It is proved that the attenuation constants of the H-shaped waveguide have better characteristics,and the attenuation constants of both of them are lower than that of the waveguide that filled with uniform medium.Furthermore,the equivalent electromagnetic current integral method is used to calculate the near field distribution at a certain height on the upper surface of the waveguide,and the results that compared with the full-wave simulation shows that the equivalent electromagnetic current integral method is also applicable to the dielectric filled elliptical leakage waveguide.