Scattering of Electromagnetic Waves by Drift Vortex in Plasma

In a quasi-two-dimensional model, the scattering of incident ordinary electromag- netic waves by a dipole-electrostatic drift vortex is studied with first-order Born approximation. The distribution of the scattering cross-section and total cross-section are evaluated analytically in different approximate conditions, and the physical interpretations are discussed. When the wavelength of incident wave is much longer than the vortex radius （kia〈〈1）, it is found that the angle at which the scattering cross-section reaches its maxim depends significantly on the approximation of the parameters of the vortex used. It is also found that the total scattering cross-section has an affinitive relation with the parameters of the plasma, while it is irrelevant to the frequency of the incident wave in a wide range of parameters of the vortex. In a totally different range of parameters when incident wave is in the radar-frequency range （then kia 〈〈 1, the wavelength of incident wave is much shorter than the vortex radius）, the numerical procedure is conducted with computer in order to obtain the distribution and the total expression of the scattering crosssection. Then it is found that the total scattering cross-section in the low frequency range is much larger than that in high frequency range, so the scattering is more effective in the low frequency range than in high frequency range.

COMPUTER VISUALIZATION OF ELECTROMAGNETIC WAVE INTERACTION WITH STRUCTURES

In this paper, a computer visualization approach is proposed for electromagnetic wave interaction with structures by mains of finite difference-time doain method (F-D) and computer graphics. By visualization of FDTD, Phenomena such as wave propagation, penetration through structures, renection and absorption by structures are observed. Visualization of electromagnetic wave interactions with two wing-shaped structures is demonstrated. These examples indicate that the approach describe in the paper offers an effective way for investigating electromagnetic wave phenomena and is helpful to the engineers in controlling radar signature of the targets.

Electromagnetic scattering from two-layered rough interfaces with a PEC object:vertical polarization

Electromagnetic （EM） scattering from a stack of two rough interfaces separating a homogeneous medium with a perfectly electric conducting （PEC） object has been calculated through the method of moments for vertical polarization. Theoretical formulations of EM scattering from multi-layered rough interfaces with a PEC object have been derived in detail and the total fields and their normal derivatives on the rough interfaces are solved. The two-layered model is a special case. In this work, a Gaussian rough surface was applied to simulate the rough interface. A cylinder was located above, between or below the two-layered rough interfaces. Through numerical simulations, the validity of this work is demonstrated by comparing it with existing scattering models, which are special cases that include a PEC object located above/below a single-layered rough interface and two-layered rough interfaces without an object. Subsequently, the influences of characteristic parameters, such as the relative permittivity of the medium, as well as the average height between the two rough surfaces, on the bistatic scattering coefficient are discussed.

Preliminary Discussion on the Relationship Between EM Wave Propagation Characteristics and Medium Parameters in Anisotropic Medium

The reflection and transmission characteristics of an anisotropic half-space medium normally illuminated by a plane wave are analyzed by kDB coordination. The general formula of reflection coefficient at the air-medium interface is given, and its validity is also discussed. The possible propagating modes in different mediums and the effect of medium parameters on these modes are emphatically studied. This work provides the theoretical preparations for the parameter reconstruction of an anisotropic material.

Bistatic RCS Prediction with Graphical Electromagnetic Computing (GRECO) Method for Moving Targets

Graphical Electromagnetic Computing (GRECO) is recognized as one of the most valuable methods of the RCS (Radar Cross Section) computation for the high frequency region. The method of GRECO and Monostatic bistatic Equivalence Theorem was used to calculate the bistatic RCS for moving targets in the high frequency region. Some computing examples are given to verify the validity of the method. Excellent agreement with the measured data indicates that the method has practical engineering value.

Conversion Technique of Vector Wave Functions:Formulas and Applications

The conversion theory of vector wave function is one of important problems in electromagnetic. This paper presents a systematic treatment of the conversion technique and some applications. In this paper, the conversion relations of standard and non-standard spherical vector wave functions, standard and non-standard cylindrical vector wave functions, and spherical and cylindrical vector wave functions are developed. As an example of application of vector wave function expansion, the expansion of plane wave and dipole field in two-medium half-spaces are given. As an example of application of vector wave function conversion, the scattering patterns of buried conducting and dielectric spheres are presented. Inspection on the numerical results shows that the technique and associated programs presented in this paper are efficient.

Factors affecting the spectrum of an electromagnetic light wave on scattering from a semisoft boundary medium

The spectrum of an electromagnetic light wave on scattering from a semisoft boundary medium is discussed within the accuracy of the first-order Born approximation. It is shown that spectral shifts and spectral switches are affected both by the polarization of the incident light wave and by the characters of the scat-tering medium. Moreover, numerical results show that the direction at which the spectral switch occurs is governed by the characters of the scattering medium, whereas the magnitude of the spectral switch is affected by the polarization of the incident light wave.

Improvements of Edges Diffraction Computing in GRECO

Graphical Electromagnetic Computing (GRECO) is one of the valuable methods for computing the radar cross section (RCS) of complex radar target in high frequency region. But there are some shortages of wedge detecting method in the original GRECO literature. A new method for collecting the edge pixels and wedge parameters is presented in this paper. An expression of edge diffraction field in the original GRECO literature is in error, the error-corrected formulas are derived by using method of equivalent edge currents (MEC) and physical theory of diffraction (PTD). Finally, the total RCS expression is given by physical optics (PO) and PTD method. The computing results are in close agreement with the measured data.

Signal Processing of the Area-Target for a Short-Range Radar

This paper presents a multi-component frequency modulation (FM) signal model for short-range radar based on the multi-points scattering model of a target, and proves that the method of computing the instantaneous frequency of single frequency is not suitable to the multi-component signal. The method of TLS-ESPRIT combining the mathematical statistics is presented for obtaining the multi-component signal instantaneous frequency (IF). The computer simulation has shown that the method has the high accuracy for measuring the distance.

Techniques for Radar Imaging Based onMUSIC Algorithm

At first, the radar target scattering centers model and MUSIC algorithm are analyzed in this paper. How to efficiently set the parameters of the MUSIC algorithms is given by a great deal of simulated radar data in experiments. After that, according to measured data from two kinds of plane targets on fully polarized and high range resolution radar system, the author mainly investigated particular utilization of MUSIC algorithm in radar imaging. And two-dimensional radar images are generated for two targets measured in compact range. In the end, a conclusion is drew about the relation of radar target scattering properties and imaging results.

Radar Cross-Section Measurement Using the Near-Field Single-Frequency Angular-Diversity Technique

Radar cross-section (RCS) measurement with the near-field electromagnetic wave illumination of a target has been proved to be practical. The existing methods employ the multiplefrequency angular-diversity (MFAD) technique, whereas this paper considers the single-frequency angular-diversity (SFAD) technique. The paper takes into account the scattering center modeling and the limitation of higher sidelobes in reconstructing images in the SFAD technique compared to the MFAD technique. A method of combining the SFAD technique with the RELAX approach is presented for the high-resolution extraction of scattering centers on a target. The proposed method offers an excellent RCS recovery, which is validated by numerical results.

Polynomial Representation of NURBS and Its Application to High Frequency Scattering Prediction

This article presents a method that uses physical optics （PO） techniques to compute the monostatic radar cross section （RCS） of electrically large conducting objects modeled by non-uniform rational B-spline （NURBS） surfaces. At the beginning, a new algorithm to convert recursive B-spline basis function into piecewise polynomials in power form is presented. Then, algorithm computes the polynomial representation of B-spline basis functions and NURBS surface geometric parameters are obtained. The PO integral over NURBS surfaces of an electrically large conducting object is used to predict the object＇s RCS. The NURBS surface is divided into small piecewise polynomial parametric patches by isoparametric curves, and the PO integral expression over the parametric domain of each polynomial parametric patch is reduced to an analytical expression which permits an accurate and effective computation of the PO integral by using a modified Ludwig＇s algorithm. The RCS of the object can be obtained by adding up the PO integral contribution of each polynomial parametric patch. The effectiveness of this method is verified by numerical examples.

Research on asymmetric “Jerusalem” unit

An asymmetric Jerusalem unit and the frequency selective surface （FSS） structure composed of such units are designed. The transmittance of the designed FSS structure is calculated by mode-matching method and compared with the test results. The comparison results show that the FSS center frequency of the asymmetric structure unit drifts little with the variation of the incident angles of the electromagnetic waves and keeps relatively stable. The research offers a new choice for the application of FSS under the large scanning angle of electromagnetic waves.