低频、甚低频电磁波过渡区传播理论研究

发布时间：2018-03-27 07:05

本文选题：低频电磁波　切入点：甚低频电磁波　出处：《浙江大学》2015年硕士论文

【摘要】：低频(LF:30-300kHz)电磁波在地面(或海面)-空气组成的两层介质中传播以及甚低频(VLF:3-30kHz)电磁波在“地-电离层波导”模型中传播问题均可看作电磁波在分层介质中的传播问题。当观察点与源点距离较小时,可忽略地球曲率的影响,采用平面半空间地波传播模型或平面波导模型来求解；随着传播距离增大,需要考虑地球曲率的影响,当满足球面模型适用条件时,可采用球面分层介质的传播模型进行求解。然而,在现有的地波传播与“地-电离层波导”传播理论尚无法解决过渡区内电磁场的理论计算,当观察点与源点的距离既不满足平面模型的距离条件,也不满足球面模型的条件时,现有的低频、甚低频电磁波的理论均不适用。对LF/VLF频段而言,过渡区范围很大,如何解决过渡区内的波传播问题有着十分重要的意义。为此,本文将针对LF地波传播及“地-电离层波导”中VLF波传播问题提出了一种新的解析计算公式,使得过渡区中的传播计算问题得到了较好的解决。本文主要工作简述如下： 1、精确定义了三种传播模型,及过渡区的截止传播距离。通过对经典低频、甚低频电磁波理论的重新审视,推导出过渡区的中心距离ρCn,并以此确定了过渡区的上下距离截止范围ρ1n、ρ2n。 2、分别提出了适用于低频电波的地波传播和适用于甚低频电波的地-电离层波导传播的分段解析模型,其中,对于过渡区的理论计算进行了明确定义与理论论证。 3、将本文所提出的理论计算模型的数值结果与King等人在地波传播过渡内的计算结果进行对比,数值结果基本一致。同时,所给出甚低频过渡区计算模型在取低阶传播模式时可退化为地波传播的过渡区模型。数值结果表明,该计算模型具有较高的数值稳定性和收敛性。综上所述,本文在现有对低频、甚低频电磁波传播问题的理论基础上,进一步提出并准确区分了过渡区的概念,引入模式加权的方法,提出了一种工程计算中适用于低频、甚低频电波在过渡区传播模型的解析表达式。通过与现有结果的对比,在与现有理论模型的求解区域数值结果吻合,并解决了现有理论中部分区域无法理论计算的不足。
[Abstract]:The propagation of low frequency LF: 30-300kHz) electromagnetic wave in the surface (or in a two-layer medium consisting of sea surface / air and very low frequency VLF: 3-30kHz) can be regarded as the propagation problem of electromagnetic wave in stratified medium. When the distance between the observation point and the source point is small, The influence of earth curvature can be ignored and solved by plane half-space ground wave propagation model or plane waveguide model. With the increase of propagation distance, the influence of earth curvature needs to be considered. The propagation model of spherical layered medium can be used to solve the problem. However, the theoretical calculation of electromagnetic field in transition zone can not be solved by the existing theories of ground wave propagation and "ground-ionospheric waveguide" propagation. When the distance between the observation point and the source point does not satisfy the distance condition of the plane model or the spherical model, the existing theories of low frequency and very low frequency electromagnetic waves are not applicable. For the LF/VLF band, the transition region is very large. How to solve the problem of wave propagation in transition zone is of great significance. In this paper, a new analytical formula for LF ground wave propagation and VLF wave propagation in earth-ionospheric waveguide is proposed. The problem of propagation calculation in the transition zone is well solved. The main work of this paper is as follows:. 1. Three kinds of propagation models are defined accurately, and the cut-off propagation distance of transition region is defined. The classical theory of low frequency and very low frequency electromagnetic wave is reexamined. The center distance 蟻 C n of the transition region is derived, and the cutoff range 蟻 1 n, 蟻 2 n of the upper and lower distances of the transition region is determined. 2. The piecewise analytical models of ground wave propagation suitable for low frequency wave wave and ground ionospheric waveguide propagation for very low frequency wave wave are presented respectively. The theoretical calculation of transition zone is clearly defined and theoretically demonstrated. 3. The numerical results of the theoretical model proposed in this paper are compared with those of King et al in the ground wave propagation transition. The model of very low frequency transition region can be degenerated into a transition zone model of ground wave propagation when the low order propagation model is taken. The numerical results show that the model has high numerical stability and convergence. To sum up, on the basis of the existing theories on the propagation of low and very low frequency electromagnetic waves, the concept of transition zone is further proposed and accurately distinguished. A method of mode weighting is introduced, and a method suitable for low frequency in engineering calculation is proposed. The analytical expression of the VLF wave propagation model in the transition region. By comparing with the existing results, the numerical results agree well with the existing theoretical model, and solve the deficiency that some regions of the theory can not be calculated theoretically.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TN011

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