Microwave and millimeter-wave propagation and scattering in dense random media: Modeling and experiments.

摘要

This thesis comprises three major components: (1) development of polarimetric millimeter-wave (MMW) scatterometer system and the associated calibration and measurement procedure, (2) development of a hybrid experimental/theoretical scattering model for bare soil surfaces, and (3) development of a novel approach for experimental characterization of the effective propagation constant in dense random media. The polarimetric MMW scatterometer system consists of network analyzer-based coherent-on-receive radars capable of measuring directly the Mueller matrix of a target. An accurate calibration technique for coherent-on-receive radars is developed which requires measuring the backscatter response of two targets: a metallic sphere and any depolarizing target (unknown scattering matrix) for four and two transmitted polarizations respectively.; The study of MMW interactions with bare soil surfaces is of importance since soil surfaces contribute to the backscatter response from different types of terrain. The MMW backscatter response of bare-soil is examined by conducting polarimetric measurements for different soil surfaces. The measured data indicate that in general the backscatter response comprises a surface scattering component and a volume scattering component. A semi-empirical surface scattering model is developed that relates the surface scattering component to the surface roughness, and the dielectric constant of the soil. The volume scattering component is modeled using radiative transfer theory.; Accurate characterization of the effective propagation constant (K) of the mean-field in a random medium is essential for predicting volume scattering from a layered random medium. Due to deficiencies in present measurement techniques, the region of validity of the analytical models used to compute K has not been examined for dense random media with fractional volumes beyond 10%. A new technique for measuring K of a dense random media is presented. In this technique, the mean bistatic scattered fields of a spherical cluster of the random medium is measured using a monostatic radar and ground plane. By searching for an effective dielectric constant, the measured response is fitted to the bistatic scattering pattern of a homogeneous sphere having an identical radius. Measurements of K at 9.5 GHz for different dense random media comprising spherical particles of different fractional volumes have shown that none of the existing models are able to predict the extinction accurately for volume fractions beyond 10%.