Scattering by a lossy dielectric cylinder in a rectangularwaveguide

Electromagnetic fields in a rectangular waveguide containing a lossy dielectric cylinder are investigated by means of the orthogonal expansion method. The calculated results are provided by measurement. Resonance effects become visible through the frequency responses of the scattering parameters and understandable by patterns due to magnetic fields and Poynting vectors. The lowest resonance is nonsymmetric and can be used to realize tunable bandstop filters with a relative 3-dB bandwidth of about 0.04 and an attenuation of more than 40 dB     

Scattering by arbitrarily cross-sectioned layered, lossy dielectric cylinders

The scattering properties of TM or TE illuminated lossy dielectric cylinders of arbitrary cross section are analyzed by the surface integral equation techniques. The surface integral equations are formulated via Maxwell's equations, Green's theorem, and the boundary conditions. The unknown surface fields on the boundaries are then calculated by flat-pulse expansion and point matching. Once the surface fields are found, scattered field in the far-zone and radar cross section (RCS) are readily determined. RCS thus obtained for circular homogeneous dielectric cylinders and dielectric coated conducting cylinders are found to have excellent agreements with the exact eigenfunction expansion results. Extension to arbitrary cross-sectioned cylinders are also obtained for homogeneous lossy elliptical cylinders and wedge-semicircle cross-sectioned cylinders, with and without a conducting cylinder in its center. RCS dependences on frequency and conductivity as well as the matrix stability problem of this surface integral equation method are also examined.     

Plasma circular cylindrical waveguide in lossy material

The surface modes in the plasma circular cylindrical waveguide in a lossy material are analyzed, particularly for the variations of their propagation properties with plasma parameters and surrounding material. The characteristic equations of surface modes are derived, and their relevant approximate solutions are given. The limit results of this paper are consistent with that given in literature’s. The analysis show that it can be used to improve the properties of mode suppressors and fabricat cut-off attenuators.     

Scattering by a cylindrical dielectric shell with inhomogeneous permittivity profile

The scattering by a plane wave incident on an infinitely long cylindrical shell is derived using the boundary-value method. The cylindrical shell is assumed to have an inhomogeneous dielectric profile in both the radial and azimuthal directions or a circular cylindrical coordinate system. The validity of the solution is verified by comparison with the method of moments. Different types of inhomogeneities are investigated and the resulting echo width as well as the scattered field pattern indicate significant variations which could be used to improve the radiation characteristics of antennas and the reradiation behaviour of scattering objects.     

High-frequency scattering by a conducting circular cylinder coatedwith a lossy dielectric of nonuniform thickness

A closed-form expression for the field produced by a plane wave incident on an infinitely long conducting cylinder, coated with a lossy dielectric of nonuniform thickness, is obtained using perturbation theory. This approximate series solution is later evaluated asymptotically for electrically large cylinder sizes. The scattered fields are interpreted using geometric optics and creeping waves. The fields are calculated using the exact series, the approximate perturbation series, and the high-frequency asymptotic solutions, and compared for different angles of incidence     

Scattering of a dipole field by finitely conducting dielectric circular cylinders

Using the differential equation approach an exact formal solution for the fields due to an axial electric dipole in the presence of a homogeneous isotropic infinite circular cylinder is obtained in integral form. An asymptotic expansion of the integral yields the far field. Patterns for different choices of the parameters are given. It is seen that for dielectric cylinders in particular, drastic departures from the perfectly conducting case can be obtained leading to more directive patterns. This in turn may have application in the design of arrays.     

Modeling of cylindrical objects by circular dielectric andconducting cylinders

The scattering of an incident plane wave from an array of parallel circular dielectric and/or conducting cylinders is derived rigorously using a boundary value approach. Both transverse electric (TE) and transverse magnetic (TM) polarized incident plane waves are considered. The validity and accuracy of the method are verified by comparing the numerical results with those based on other available methods. The advantage of the proposed analysis is the simplicity and efficiency in computation. The modeling of two-dimensional objects of arbitrary cross section and composite material is outlined and sample numerical results are presented to illustrate the versatility of the method     

Scattering from an anisotropic cylindrical dielectric shell

The electromagnetic scattering from an anisotropic cylindrical dielectric shell is formulated by using the wave functions for anisotropic media and the boundary-value method. The cylindrical shell is assumed to be infinite in length, and it is illuminated by a plane wave or a cylindrical wave from a line source. The problem is two-dimensional and the solutions to both types of polarization (TE and TM) are presented. Numerical results for the effects of various geometrical and electrical parameters on the bistatic radar cross section are presented.     

Scattering by an infinite circular dielectric cylinder coating eccentrically an elliptic dielectric cylinder

Scattering of a plane electromagnetic wave by an infinite circular dielectric cylinder coating eccentrically an elliptic dielectric one, is under consideration. Both E and H polarizations are treated for normal incidence. The electromagnetic field is expressed in terms of both circular and elliptical-cylindrical wave functions. Using proper transformation theorems between the field expressions in different coordinate systems, for the satisfaction of the boundary conditions, we obtain two infinite sets of linear nonhomogeneous equations for the expansion coefficients of the field. In case of small values of h=k/sub 2/c/2, where c is the interfocal distance of the elliptic cylinder and k/sub 2/ the wavenumber of the dielectric coating, the former sets of equations provide, by truncation, semianalytical expressions of the form S(h)=S(0)[1+gh/sup 2/+O(h/sup 4/)] for the scattered field and the various scattering cross sections. The coefficients g are independent of h. Graphical results for the scattering cross sections are given for various values of the parameters.     

Scattering from a metallic object embedded near the randomly roughsurface of a lossy dielectric

Two-dimensional electromagnetic scattering from a perfectly conducting target embedded near the randomly rough surface of an isotropic lossy dielectric is investigated. The randomly rough surface is illuminated by a finite width beam from an antenna in the free space above the surface, with off-normal incidence. Standard integral equation methods are applied and include all subsurface interactions between the object and rough surface. For a chosen embedded target, Monte Carlo simulations are performed for a selection of ensembles of rough surface types intended to be suggestive of natural ground. Far field scattering coefficient distributions and corresponding synthetic images suggest when the buried object should be discernible. Sensitivities are explored in terms of surface type, polarization of the incident field, depth and orientation of target, soil characteristics, incidence angle, and beamwidth. Many of the scattering features identified should also apply in 3D     

Scattering by a multilayer chiral cylinder

An efficient recursive eigenfunction solution for the problem of scattering by a multilayer chiral circular cylinder, with or without a surface impedance center cylinder, is presented. For an M layer cylinder, the solution requires the multiplication of M4×4 matrices, versus the solution of a 4M×4M matrix equation in a standard approach. The problem of a transverse electric (TE) incident plane wave differs from that of a transverse magnetic (TM) wave only by a plus/minus sign at one step in the solution. The addition of the surface impedance center cylinder requires only one additional matrix multiplication. Numerical results, including echo width and internal fields, are presented for several sample cylinders     

Extended spectral domain approach for analysis of lossy cylindrical dielectric resonators

The spectral domain approach is extended for evaluating both the resonant frequency and Q factor of a lossy cylindrical dielectric resonator operating in TE/sub 0/ modes, taking into account the effects of conducting enclosure and supporting substrate. On the basis of the equivalence principle, the circular electric currents are introduced to simulate the fields inside and outside the cylindrical dielectric sample, which separates the original problems into two auxiliary structures with radially homogeneous multilayered dielectrics. Using the spectral immittance method in conjunction with the point-matching method, the characteristic equations are derived. The present technique has no need to determine the time-consuming, complex higher-order modes. Some typical examples are computed. The numerical results agree well with experimental data available in the literature.<>     

Scattering from a circular dielectric post embedded in a groundeddielectric sheet waveguide

A systematic method for obtaining the scattered electric field in a grounded dielectric sheet waveguide is presented. It is shown that the point-matching method can be used for an explicit calculation of the integral equation to estimate the scattering from a circular dielectric post embedded in the grounded sheet. The magnitude of the reflection coefficient as a function of dielectric constant is given     

Electromagnetic scattering by weakly lossy multilayer ellipticcylinders

The analytic solution to the electromagnetic scattering due to a multilayer elliptic cylinder is generalized to the case of weakly lossy materials by using a first-order truncation of the Taylor expansion of each Mathieu function     

Scattering by a rotating dielectric sphere

The scattering of a plane wave by a rotating dielectric sphere of arbitrary radius,epsilon_{r}andmu_{r}is investigated. A relativistically correct solution is found for the scattered fields and the fields inside the sphere. This solution is valid in the limit of "small" angular velocities. Attention is focused on the fields at large distances. The depolarization of the backscattered signal and the scattering in the low frequency limit are treated in some detail.     

Scattering by an infinite circular dielectric cylinder coatingeccentrically an elliptic metallic one

The scattering of a plane electromagnetic wave by an infinite-circular dielectric cylinder, containing eccentrically an elliptic metallic one is considered. The electromagnetic field is expressed in terms of both circular and elliptical-cylindrical wave functions, connected with one another by well-known expansion formulas. Translational addition theorems for circular cylindrical wave functions are also used for the satisfaction of the boundary conditions in the dielectric cylinder. When the solution is specialized to small values of h=k₁c/2, with k₁ the wavenumber of the dielectric cylinder and c the interfocal distance of the elliptic conductor, semianalytical expressions of the form S(h)=S(0)[1+gh²+O(h ⁴)] are obtained for the scattered field and the various scattering cross sections of this configuration. Both polarizations are considered for normal incidence. Numerical results are given for various values of the parameters     

Scattering by two-dimensional lossy, inhomogeneous dielectric andmagnetic cylinders using linear pyramid basis functions and pointmatching

A volume integral equation approach is used to calculate the scattering characteristics of lossy, inhomogeneous, arbitrarily shaped, two-dimensional dielectric and magnetic bodies. The scatterer is divided into triangular patches, which simulate curved and piecewise linear boundaries more closely than circular cylinder cells. Linear pyramid basis functions are employed to expand the unknown total electric field at the triangle nodes. The enforcement of the boundary conditions by point matching at the nodes converts the electric field integral equation to a matrix equation. Example cases are run and compared to previous moment methods and exact solutions, and this method shows good agreement. This method requires only one unknown per node in dielectric and magnetic material, which is a significant reduction in unknowns and matrix storage compared to traditional methods. By duality, this method can be used at either transverse electric or transverse magnetic polarization     

Scattering from dielectric cylindrical shell periodically loaded with metallic patches

A dielectric cylindrical shell that is covered with metallic patches is considered. Entire domain basis functions are employed in the moment method solutions and the infinite sums are accelerated by Kummer's method. Results show that the radar cross-section of the structure vanishes at some specific frequencies.     

Scattering by dielectric containers

The radar cross section (RCS) has been derived by an approximate method for a thin dielectric plate and for thin spherical and conical dielectric shells. The computed results for a flat plate and a conical shell are compared with experimental patterns. The computed results for a conical shell are presented in the form of constant RCS contours on the aspect angle-frequency plane.     

Scattering from conducting loops and solution of circular loop antennas by numerical methods

The integral equation of the current distribution along a circular loop antenna is solved by numerical methods. The integral equation is converted into a set of linear simultaneous equations, whose solution gives the desired current distribution. First, the loop antenna driven by a voltage source is considered and solutions to loops of various sizes are obtained. Secondly, current distributions are obtained for the loop as a scatterer illuminated by a plane wave. Finally, from the knowledge of the current on the illuminated loops, backscattering patterns are obtained for loops as a function of the rotation angle. The results of measurements for the latter case are also presented and compared with the calculations.