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Study of the scattering of electromagnetic waves from certain types of random media Olsen, Roderic Lloyd


This work is a study of the scattering of electromagnetic waves from random media of discrete scatterers. The object is primarily the investigation of existing general discrete-scatterer theories and the development of more accurate ones, the technique of Monte Carlo computer simulation being employed to provide "exact" experimental results for comparison with theoretical data. A one-dimensional model of randomly-positioned planar scatterers is used as a tool in the investigation and as a means of providing insight into the physical and statistical characteristics of discrete-scatterer media. The limitations of the one-dimensional forms of Twersky's theories for the coherent field are illustrated by a presentation of results for a wide range of scattering parameters, and requirements necessary for the approximate validity of these theories are given. Accurate series expressions for several average field functions of interest in the problem of plane-wave scattering from distributions of uniformly-random planar scatterers are presented and verified from simulation results. The asymptotic scattering behavior for a low average density of scatterers is emphasized; a modification to the one-dimensional form of Twersky's free-space theory for the coherent transmitted field to give exact asymptotic behavior is shown to be a considerable improvement for higher average densities also. The relation of the one-dimensional model theory and results to more complex three-dimensional models is discussed where possible. Simulation methods for the generation of a non-uniform distribution of planar-scatterer configurations weighted towards "periodicity" are presented. Based on the scattering results obtained, criteria for the assumption of a uniform distribution are given. The physical conditions necessary for the approximate validity of the bivariate Gaussian distribution in describing the total field statistics of the one-dimensional model are discussed and quantitative results based on the third and fourth field moments given. Also presented is a new physical model of a random medium of discrete spherical scatterers for use in controlled laboratory experiments at millimeter-wave frequencies. The main feature of this model is that the scatterer statistics are directly controlled by an application of the Monte Carlo method. The results of an experimental investigation into the suitability of the model are given.

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