Full-wave solutions for the scattered radiation fields from rough surfaces with arbitrary slope and frequency

Full-wave solutions are derived for the scattered radiation fields from rough surfaces with arbitrary slope and electromagnetic parameters. These solutions bridge the wide gap that exists between the perturbational solutions for rough surfaces with small slopes and the quasi-optics solutions. Thus it is shown, for example, that for good conducting boundaries the backscattered fields, which are dependent on the polarization of the incident and scattered fields at low frequencies, become independent of polarization at optical frequencies. These solutions are consistent with reciprocity, energy conservation, and duality relations in electromagnetic theory. Since the full-wave solutions account for upward and downward scattering, shadowing and multiple scatter are considered. Applications to periodic structures and random rough surfaces are also presented.     

Full wave and physical optics solutions for scattered radiation fields by rough surfaces-energy and reciprocity relationships

Full wave and physical optics solutions for the scattered radiation fields from rough surfaces are compared. The full wave solutions involve complete expansions of the fields and exact boundary conditions. The solutions for the radiation fields axe provided in a form that can be readily compared with earlier solutions to the problem, and they can be applied directly to engineering problems without the need to carry out any of the analytic procedures encountered in the derivations. The surface impedance concept, reciprocity, and energy conservation relationships are considered in detail, and special consideration is given to grazing incidence and excitation at the Brewster angle. This work on irregular ground effects on radio wave propagation is relevant to problems of communication, navigation, and active remote sensing.     

Scattering and depolarization by rough surfaces near grazing angles--Full wave solutions

Using the full wave approach to rough surface scattering, the apparent singularity in the physical optics and perturbation expressions for the scattered fields is not encountered. The full wave expression for the far fields is shown to vanish in a continuous manner as the observer moves across a shadow boundary. Precise criteria are given for near grazing angles where uniform plane wave excitations cannot be assumed. Comparisons are made between the full wave and the physical optics and perturbation solutions. Since the full wave solution is shown to bridge the gap between the physical optics and perturbation solutions, it accounts for both specular and Bragg scattering. The full wave solutions satisfy reciprocity, duality, and realizability relationships in electromagnetic theory, and they are invariant to coordinate transformations.     

Mode-expansion method for calculating electromagnetic waves scattered by objects on rough ocean surfaces

A mode-expansion method that needs less than 6% the number of unknowns required by conventional method of moments is introduced in calculating two-dimensional electromagnetic wave scattering from perfectly conducting objects on rough ocean surfaces. Modes are selected for dominant propagation waves so that the number of unknowns in the matrix equation are minimized. In the numerical examples, ocean surfaces are modeled as perfectly conducting rough surfaces described by the Pierson-Moskowitz power spectrum. Bistatic radar cross-sections (RCS) of various objects, such as ship-like and low-observable targets, are calculated for a 1-GHz incident plane wave and are validated for accuracy against an iterative MoM solution.     

EM fields generated by lightning channels with arbitrary locationand slope

It is well known that lightning discharges follow a tortuous path; therefore, a general technique able to evaluate the electromagnetic (EM) fields associated with discharge currents flowing into tortuous channels seems to be worthy of consideration. Two techniques have been adopted to find the EM field generated by a current pulse traveling along a single line radiator with arbitrary slope and location above the ground. The first one employs the Fraunhofer approximation, which can provide useful information only on distant radiated fields. The second technique is exact, but applies only to the case of a velocity of propagation v of the current pulse equal to c (velocity of light). Even this solution is indeed inadequate for our purposes since v相似文献   

Near-zone fields scattered by three-dimensional highly conductingpermeable objects in the field of an arbitrary loop

An efficient numerical technique is presented for electromagnetic scattering in the near-field zone by three-dimensional permeable conducting objects excited by a loop antenna. The impedance boundary conditions are used to simplify the formulation and reduce the computation time and memory. Numerical results are presented to illustrate the dependence of the scattered field on the physical characteristics of the scatterer and its location     

An iterative algorithm for calculation of the field scattered by a rough surface

A technique is developed for calculation of the field scattered by a rough surface in the specular direction in the case of grazing illumination angles.     

基于高阶叠层矢量基函数的加速迭代求解方法

提出了一种基于双线性思想的高阶基函数降低矩量法分析介质目标电磁散射问题时的未知量.论文给出了双线性高阶叠层基函数的构造过程, 并将其应用于介质的面积分方程分析中.数值算例比较了不同阶数时所需未知量以及计算精度, 表明该高阶叠层基函数在满足相同积分方程的计算精度时能比低阶基函数节省未知量.     

Backscattering of waves by composite rough surfaces

A general theory of electromagnetic wave scattering is developed using the Stratton-Chu integral as modified by Silver for a gently undulating homogeneous surface on top of which small irregularities are superimposed. It is assumed that the tangent-plane approximation is applicable to the undulating surface so that the local fields can be evaluated by considering a slightly perturbed plane surface. Average powers, both polarized and depolarized, are calculated for the composite surface whose statistical properties are assumed known. Shadowing effects are also included before comparing with experimental results. The comparison between the moon data and the data obtained under laboratory conditions shows very good agreement. The same surface parameters are used for both the polarized and the depolarized returns. Previous theories cannot provide a connection between the parameters used in the polarized return expression and those in the corresponding depolarized expression since only a single-surface model was considered. The results indicate that polarized returns of near vertical incidence are dominated by the large-scale roughnesses, while the depolarized returns are affected by both the large and small roughnesses. As the incident angle increases, the effect of small irregularities becomes increasingly important for both the polarized and the depolarized returns. The cause of depolarization and diffuse scattering, as shown in this theory, is the perturbation of the fields on the surface by the small irregularities.     

Electromagnetic radiation from structures consisting of combinedbody of revolution and arbitrary surfaces

A formulation is developed to treat radiation from structures consisting of a body of revolution (BOR) in the presence of multiple arbitrarily shaped three-dimensional objects. An electric field integral equation is set up on the surface of the combined structure. The resulting integro-differential equation is solved using the method of moments. On the BOR, harmonic entire domain expansion functions are used for the circumferential dependence, while overlapping subdomain functions are used to model the axial curvature. The arbitrarily shaped portions of the structure are modeled using triangular surface patches. The resulting system matrix has a partial block diagonal nature, which provides a more economical solution for structures that have some rational symmetry. Numerical results are presented and compared to measurements of a unique cavity-backed patch fed antenna     

Note on the scattering of waves by rough surfaces

A calculation of back scattering from a rough surface using Huygen's principle is carried out along the lines introduced by Davies. Davies original equation is extended to include a contribution from the component of the surface normal which is parallel to the average surface. The effect of this component is to multiply the usual expression for incoherent backscatter by a factor of1/ cos^{4} PsiwherePsiis the angle between the radar line of sight and the normal to the average surface.     

Analytical, experimental, and numerical studies of angular memorysignatures of waves scattered from one-dimensional rough surfaces

It is known that a change in the direction of an incident wave on a random medium is “remembered” by the angular correlation characteristics of the scattered waves. This “memory effect” is studied for rough-surface scattering by means of theoretical [second-order Kirchhoff approximation (KA)], numerical (Monte Carlo simulations), and experimental (millimeter-wave range) approaches. The second-order KA has been found to be effective for wave scattering from very rough surfaces with large radii of curvature and high slopes (0.5-1.5). Although the second-order KA is based on a number of approximations including the geometrical optics approximation and the approximate forms of the shadowing functions, excellent agreement with Monte Carlo simulations and millimeter-wave experiments was achieved. The results are presented in a form of memory signatures which clearly exhibit the important features of this effect     

Sampling approach for fast computation of scattered fields

The letter describes an efficient computational technique, based on a sampling approach, of the evalution of the far-field radiation integral of an arbitrary source distribution. The technique virtually eliminates any redundancy of computation by reducing to a minimum the number of elements of information required for a satisfactory radiated field reconstruction. These elements, in turn, can be efficiently computed by a proper fast Fourier transform algorithm.     

On the spatial bandwidth of scattered fields

It is shown that the scattered fields are almost space bandlimited functions. The effective bandwidthWis introduced and evaluated for a very general scattering system, as well as the error made using functions bandlimited tow > Wfor representing the scattered field. The effective bandwidth is very simply related to the maximum dimension of the scattering system; the error drops to negligible values for modest increases ofwcompared toW, in the case of large scatterers. Important consequences of the above general results are finally stressed.     

Analysis of the accuracy of an iterative algorithm for calculating the field scattered by a rough surface

The accuracy of an iterative algorithm for calculating the field scattered by a rough surface in the mirror direction is estimated for grazing angles of incidence.     

Wave diffraction by a rough boundary of an arbitrary plane-layeredmedium

The problem of electromagnetic (EM) wave scattering by a slightly rough boundary of an arbitrary layered medium is solved by a small perturbation method. The bistatic amplitude of scattering as well as scattering cross sections for a statistically rough surface are calculated for linear and circular polarized waves. Along with the scattering into the upgoing waves in the homogeneous medium, the scattering cross sections in the downgoing waves into a layered medium are obtained. Analytical results are applied to the modeling of natural layered media (ice and sand layers) remote sensing problems employing global positioning system (GPS) technics     

Representation of electromagnetic fields over arbitrary surfaces bya finite and nonredundant number of samples

It is shown that the electromagnetic (EM) field, radiated or scattered by bounded sources, can be accurately represented over a substantially arbitrary surface by a finite number of samples even when the observation domain is unbounded. The number of required samples is nonredundant and essentially coincident with the number of degrees of freedom of the field. This result relies on the extraction of a proper phase factor from the field expression and on the use of appropriate coordinates to parameterize the domain. It is demonstrated that the number of degrees of freedom is independent of the observation domain and depends only on the source geometry. The case of spheroidal sources and observation domains with rotational symmetry is analyzed in detail and the particular cases of spherical and planar sources are explicitly considered. For these geometries, precise and fast sampling algorithms of central type are presented, which allow an efficient recovery of EM fields from a nonredundant finite number of samples. Such algorithms are stable with respect to random errors affecting the data     

Transient scattering by conducting surfaces of arbitrary shape

The time-domain electric field integral equation (EFIE) is used along with the method of moments to develop a simple and efficient numerical procedure for treating problems of transient scattering by arbitrary shaped conducting objects. The conducting surface is modeled by planar triangular patches for numerical purposes. Because the EFIE is used in the solution procedure, the method is applicable to both open and closed bodies. the EFIE approach is applied to the scattering problems of Gaussian plane wave illumination of a flat square plate and sphere. Comparisons of surface current densities and far-scattered fields are made with previous computations and good agreement is obtained in each case     

Depolarization of EM waves by slightly rough surfaces

Depolarization is obtained for the scattering of electromagnetic waves from a slightly rough surface using Rice's theory. In the plane of incidence, depolarization is a second-order effect. The results are applied to backscattering from a slightly rough sea using the Neumann spectrum for a fully developed sea. The expression for the depolarized scattered power is of the form obtained in multiple scattering investigations. Therefore, it can be inferred that depolarization from slightly rough surfaces is due to multiple scattering. For the sea, depolarization increases with wind speed and with the magnitude of the complex dielectric constant of the surface.     

A hybrid method for computing the scattered fields from complexstructures

A new hybrid method that removes typical discontinuities and singularities of UTD solutions is described and applied to scattering by complex structures. The scattered fields from the structure are first computed on a surface S enclosing it. Then these fields are used to compute an equivalent set of electric and magnetic currents, which are then used to find the scattered fields from the structure. This method can extend the ability of available UTD computer codes to solve for the scattered fields from structures that need special treatment and are nor solvable through direct UTD means. Good agreement is shown between this new hybrid method and moment method results as well as measurements