Study On The Analysis Method For Radio Wave Propagation Characteristics In Large-scale Environments Based On Parabolic Equation And Its Applications

With the rapid development of the wireless technology,more and more attention has been paid to the complex electromagnetic environment in recent years.In order to evaluate the electromagnetic environment quantitatively,a reliable electromagnetic analysis method is required in many fields,such as the radar system design and performance evaluation,radar emitter recognition,channel optimization of wireless communication system,electromagnetic compatibility analysis and electromagnetic interference suppression,et al.However,when the regional-level scenes are involved in computation,the widely used full-wave numerical methods,high-frequency approximation approaches,and empirical models are usually not suitable due to the defect of computational efficiency or accuracy.The parabolic equation(PE),which is derived from the Helmholtz equation,can provide an adaptive and accurate description of the reflection,refraction,and diffraction of electromagnetic waves caused by irregular terrains and various propagation media.Moreover,the parabolic equation has the virtues of fast calculation and low memory consumption.Therefore,it is very suitable for the prediction of the radio wave propagation in the large-scale complex environment.This dissertation focuses on an analysis method of radio wave propagation characteristics based on the parabolic equation.Several key technologies,including the hybrid algorithm of method of moment(MOM)and ultra wide-angle parabolic equation,estimation methods of pulse characteristic parameters,optimization method of the wireless channel,and regional-level EMI analysis method,are presented and detailed.The main work of this dissertation is summarized as follows:Firstly,a hybrid algorithm which integrates the MOM and ultra wide-angle parabolic equation is presented.Due to the paraxial approximation,the propagating components at large angles can not be modelled by the traditional parabolic equation.Therefore,a three-dimensional(3-D)high-order Padé version is introduced in this study and an alternating direction implicit(ADI)finite difference scheme is derived.Numerical examples are presented to verify the correctness of this scheme.Furthermore,a two-way counterpart of the high-order Padé PE is presented and applied to the prediction of radio wave propagation in the urban environment.Numerical results show that the presented method can describe the large angle components and backscattering components produced by the buildings.Then,an efficient hybrid algorithm is established by combining the MOM and 3-D high-order PadéPE,so as to implement an integrated modeling of antenna radiation and radio wave propagation.The presented hybrid method can model the scattering and coupling effects of the antenna platform and the obstacles near the radiation source,which results in a higher accuracy than the traditional methods.Secondly,several parabolic-equation-based methods for estimating the characteristic parameters of the pulses in the troposphere is presented.The widely used parabolic equation is essentially a frequency-domain method,which indicates the synthetic amplitude and phase from different harmonic paths.The modeling of pulse-compression signals propagating in the troposphere is implemented via the multi-frequency calculation and Fourier synthesis in the study.Several effective methods,in combination with the parabolic equation,are presented to estimate the pulse delay,arrival of angle,envelope,and instantaneous frequency,which facilitates a multi-dimensional feature description of the electromagnetic signals in the troposphere.With these methods,the influences of evaporation duct on radar pulse-compression signals are analyzed and studied.Besides,a parabolic-equation-based method for generating radar pulse description words(PDWs)is presented,which can provide data support for radar performance evaluation and emitter identification in a complex environment.Thirdly,the parabolic equation is applied to estimate and optimize the wireless channel in tunnels.The transfer function and impulse response of the wireless channel are expressed with the parabolic equation and time-frequency transform theory.Based on the high-order Padé PE and its ADI solution,a model describing the propagation of radio waves in tunnels is established and verified by using the mode theory.The frequency responses of the wireless channel in straight and curved tunnels are studied.In addition,an antenna diversity optimization method using the parabolic equation and differential evolution is proposed for multi-path fading channels.The diversity configurations matching the environment are obtained via optimizing the installation positions,layout and feed phases of the antenna elements.The presented method is applied to railway tunnels,and the simulation results show that the deep fading phenomenon can be alleviated and the quality of mobile communication is thus effectively improved.Fourth,an efficient dual-scale method,which combines PE and MOM,is presented to study the EMI problems in complex environments.For the field-line coupling analysis,PE is used to model the complex spatial field distribution,so as to obtain an accurate excitation for the thin-wires.Then,the integral equations are established by the electromagnetic boundary conditions of the wire conductors.Finally,the currents induced on the wires are solved by using the MOM.Besides,a novel dual-scale method integrating PE and RWG-MOM is proposed.The original solution is decomposed into two parts: the calculation of electromagnetic fields surrounding the electronic devices and the modeling of ambient waves coupling to electronic devices.Compared with the full-wave electromagnetic methods,the proposed method reduces the memory and computing time effectively.As a result,it is particularly suitable for EMI analysis in a regional-level scenario.