Gaussian beam scattering from a conducting cylinder partially buried in a ground plane

The problem of scattering from an infinitely long conducting cylinder that is partially buried in a perfectly conducting ground plane due to an obliquely incident gaussian beam is solved by an exact procedure based on the method of images by first adopting a simplification originally proposed by Kozaki. The incident and the specularly reflected fields are expressed in terms of cylindrical vector wave functions multiplied by a weighting function which involves the beam parameters like the radial distance of the source and beam width. The scattered fields originating from the cylinder and its image in the ground plane are expressed in terms of cylindrical vector wave functions. The boundary conditions on the surface of the cylinder are then imposed and this procedure leads to a coupled infinite system of equations for the even and odd mode expansion coefficients of the scattered field. These equations are solved numerically for the case of cylinders having electrical radius in the Rayleigh and resonance regions. Both the transverse magnetic and transverse electric polarizations of the incident beam wave are considered and some representative numerical results for the scattered far-field are presented in graphical form. The magnitude of the induced current for the TM polarization is calculated and compared with the corresponding case of plane wave incidence.     

单层和双层手征介质柱域的并矢格林函数理论及其应用

本文应用散射叠加法,分别导出了单层和双层手征介质圆柱区域中的并矢格林函数。由此分析了位于手征介质圆柱和手征介质圆柱罩中心轴线上点偶极天线的辐射特性。结果表明,通过改变手征介质圆柱的尺寸和手征介质圆柱罩的厚度,可以任意调节辐射场的极化特性。另外,本文给出的并矢格林函数公式还可用于分析柱形手征微带天线的辐射特性。     

Calculation of the acoustic radiation field at the surface of a finite cylinder by the method of weighted residuals

In the design of sonar systems it is desirable to compute the acoustic radiation field at the transducer surface, upon which all the significant radiation properties (radiation impedance, beam patterns, etc.) depend. Like other practical array geometries of interest, the finite cylinder does not belong to the class of separable coordinate surfaces of the Helmholtz equation, and consequently, the acoustic field for this geometry cannot be determined analytically. In this paper the surface field is computed numerically from the interior Helmholtz integral equation by the method of weighted residuals. Since the pressure fields over the three surfaces of the finite cylinder must coincide along the locii of intersection between the cylindrical surface and the end caps, the interior Helmholtz integral equation must he constrained to meet this requirement. The matrix representation of this equation which is not self-adjoint is solved by the method of least squares. This enables the constraints to be introduced via Lagrange multipliers. The procedure is used to calculate the surface pressure and radiation impedance of the finite cylinder for a range of axis ratios (diameter/length) and frequencies of interest in sonar applications. Calculations of the radiation resistance and the directivity index determined in this manner are shown to differ from those previously evaluated from the far-field solution. The weighted-residual methods considered are shown to have excellent convergence properties which make them more versatile than alternative numerical methods for solving the problem.     

A computational methodology and results for quasistaticmultilayered magnetic shielding

A methodology for accurate calculations of shielding factors for quasistatic multilayered magnetic shields is described. “Transfer relations” for individual layers with specified magnetic permeabilities and electrical conductivities are spliced together. Specific transfer relations for four layer geometries (planar, cylindrical with transverse fields, cylindrical with axial fields, and spherical) and constraints at source and shielded surfaces for six source-shield configurations involving both externally applied fields and enclosed sources are developed. Limiting cases are extracted for magnetically permeable, nonconducting layers, and for thin, magnetically nonpermeable, conducting layers. Reciprocity conditions are identified for interchanged source and shielded regions in planar, transverse field cylindrical, and spherical geometries. Variations of magnetic field and flux density with position are shown for a specific planar example involving alternating layers of aluminum and steel, with the same total shield thickness occupied by either one or five layer pairs. Simulations with alternating layers of aluminum and steel for the four layer geometries are used to study the effects of material composition, number of layer pairs, and air gaps. An optimal number of layer pairs for a given total shield thickness is identified. Results from simulations where induced currents in the steel layers are neglected are compared with those for simulations with a realistic conductivity value for steel to assess the relative effects of flux shunting and induced current shielding     

Attenuation in a dielectric elliptical cylinder

The problem of the propagation of electromagnetic waves along a dielectric cylinder of elliptical cross section is considered. There exist two dominant waves which possess zero cutoff frequencies. The attenuation characteristics of these dominant waves are analyzed theoretically and experimentally. Good agreements are obtained. It is shown that one of the dominant waves, with its electric fields parallel at the center of the cylinder to the minor axis of the elliptical cylinder, can propagate along a flat dielectric strip with much lower loss than can theHE_{11}wave along a circular cylinder having the identical cross-sectional area.     

Radiation by a corner reflector with dielectric loaded edges

The first part, of this paper deals with the electromagnetic scattering by a cylindrical dielectric shell with an azimuthal permittivity profile and an internal E-polarized line source or an externally incident plane wave. The integral equation for the resulting scattered electric field is solved approximately by the method of moments and the results for the echo width and polar radiation pattern are displayed graphically for typical geometrical dimensions, frequency and permittivity profiles.

The second part of this paper deals with the cylindrical dielectric shell terminating a conducting strip with one edge coinciding with the axis of the cylinder. The results for the scattered field due to a line source excitation are presented and extended to the case of two such strips whose unloaded edges intersect to form a corner reflector antenna. The resulting radiation pattern is shown to improve for specific dimensions and complex permittivity profiles of the dielectric caps.     

Localizing the spatial and temporal electromagnetic fields on theaxis of a lossy cylinder

Given a specified form, both in time and space, for the electromagnetic fields on the axis of a lossy cylinder, the authors determine, analytically, the required azimuthally symmetric source distribution on the surface of the cylinder that generates such internal fields. They then show that this source is equivalent to an array with finite number of cylindrical slots in a metal encasing that are impulsed by specified voltages at a finite sequence of discrete times. A confirming forward calculation exhibits excellent agreement between the specified field form and that generated by the array of cylindrical slots. Potential applications are to hyperthermic cancer therapy, bioelectromagnetics and nondestructive testing     

Crosspolarisation characteristics of cylindrical triangularmicrostrip antennas

Crosspolarisation characteristics of triangular microstrip antennas mounted on a cylindrical body are studied using a full-wave analysis. Numerical results of the far-zone copolarised and crosspolarised radiated fields at the TM₁₀ mode for different cylinder radii and flare angles are calculated and analysed. A significant dependence of the crosspolarisation level on the cylinder radius and flare angle is observed. Details of the results are presented     

Optimum cylindrical near fields for illuminating a spherical reflector

A spherical reflector antenna can be illuminated by a radiating line source along its symmetry axis. The optimal fields on a cylinder around this axis are found using a modal expansion technique. The optimal fields are expressed as combinations of cylindrical harmonics with unknown mode coefficients and set equal to the required illumination on the sphere. The resultant integral equations are solved using steepest descent methods, giving the mode coefficients. These coefficients are then checked by numerical integration. The optimal cylindrical fields are found from these mode coefficients both by integrating numerically and by steepest descent methods. The results of both techniques are checked by numerical integration. The results give theoretical aperture efficiencies of greater than 90 percent at sufficiently short wavelengths.     

The application of antenna theory to the calculation of electric shielding due to metallic reinforcement in a cylindrical shelter

Reinforcement bars arranged longitudinally around an antinuclear cylindrical shelter are treated as coupled dipole antennas and are shown to provide shielding against EMP which is a maximum at the shelter center and drops steeply towards the ends unless the reinforcement is continued into the end caps. Depending on dimensions, a low frequency electric field parallel to the cylindrical axis can be shielded by a factor of the order of 10 to 35 dB or more.     

A new hybrid mode-matching/numerical method for the analysis ofarbitrarily shaped inductive obstacles and discontinuities inrectangular waveguides

A new and efficient hybrid mode-matching method is presented for the analysis of arbitrarily shaped inductive obstacles and/or discontinuities in a rectangular waveguide. The irregular region with obstacles and/or discontinuities is characterized using a full-wave hybrid spectral/numerical open-space technique expanding the fields in cylindrical wave functions. Next, a full-wave mode-matching procedure is used to match the cylindrical wave functions to guided modes in all ports and a generalized scattering matrix for the structure is finally obtained. The obstacles can be metallic or dielectric with complex permittivities and arbitrary geometries. The structure presents an arbitrary number of ports, each one with different orientation and dimensions. The accuracy of the method is validated comparing with results for several complex problems found in the literature. CPU times are also included to show the efficiency of the new method     

Scattering by a Conducting Infinite Cylinder Illuminated with a Shaped Beam

An analytic solution to the shaped beam scattering by a conducting infinite cylindrical particle is constructed within the framework of the generalized Lorenz-Mie theory (GLMT). The expansion coefficients of the scattered electromagnetic fields are derived by using the boundary conditions. As an example, for a tightly focused Gaussian beam propagating perpendicular to the cylinder axis, the scattering characteristics that obviously demonstrate the three-dimensional nature, as with the case of a dielectric infinite cylinder, are described in detail, and numerical results of the normalized differential scattering cross section are evaluated.     

Analysis of microstrip antennas on circular-cylindrical substrateswith a dielectric overlay

The use of dyadic Green's functions and the moment method is explored for the solution of microstrip antenna problems on circular cylindrical substrates. The dyadic Green's functions of the electric type are obtained for a medium consisting of three cylindrical dielectric layers concentric with a perfectly conducting cylinder, and integral equations are developed for the evaluation of the electromagnetic fields. The effect of a dielectric overlay on the resonant frequency of a cylindrical-rectangular microstrip antenna is analyzed. The patch is directly fed by means of a microstripline printed along the cylinder axial direction. The results show that the effect of the dielectric overlay is substantial when its relative permittivity and thickness are increased, such that this effect has to be very carefully considered in the design of microstrip antennas     

Circumferential distribution of scattering current and small hole coupling for thin finite cylinders

The scattering current induced on a thin finite conducting cylinder immersed in a"theta"-polarizedE-field is studied. Particular attention is paid to the circumferentially nonuniform mode as theE-field angle of incidence varies. This nonuniformity is shown significant (peak-to-average ratio of 3 dB at cylinder midlength) at certain incidence angles for wavelength long cylinders with diameters as small as0.067lambda. Also investigated is the relationship between scattering current and cavity response patterns for narrow thin-walled cylindrical cavities with small holes through which energy is coupled. It is demonstrated theoretically, with experimental verification, that the circumferential variation of scattering current strongly affects the fields within thin cylindrical cavities having apertures with small circumferential extents. It is noted, however, that for most thin-body radiation and scattering problems (in contrast with aperature coupling) only the uniform current mode is significant.     

Analysis of Electromagnetic Waves Scattering by a Finite Size Dielectric and Metal Cylinder in a Rectangular Waveguide

The paper presents a rigorous solution of the scattering problem by a circular dielectric and perfectly conducting cylinders of any radius and any height in the rectangular waveguide oriented perpendicularly to a wall. The method is based on the representation of fields in waveguide and dielectric medium by cylindrical eigenfunctions and application of boundary conditions on surfaces of the cylinder to evaluate the fields inside and outside the cylinder. The reflection and transmission coefficients are expressed through the fields. As an example the reflection and transmission coefficients versus frequency for various dielectric and metallic cylinders are computed. The comparison of numerical with experimental data is presented.     

Research on dual-polarized circular waveguide antenna fed by L-shaped probes

This paper researched a kind of dual-polarized and cylindrical waveguide antenna fed by two L-shaped probes at the antenna bottom. The designed antenna was composed of two orthogonal L-shaped coaxial probes and a cylindrical waveguide cavity. The two orthogonal field structures were excited and the dual-polarized radiation mode was formed. The feeding cables of two polarization ports went through the bottom of the cylindrical cavity and were connected with the microwave adaptors. The bottom feeding structure was suitable to constitute a planar antenna array. The electromagnetic simulation and optimization design of the proposed antenna were carried out by using the full wave electromagnetic simulation technique, and the simulation results showed that the isolation between two polarization ports were more than 20 dB within the frequency range of 4.8–5.4 GHz. At the center frequency, the cross-polarization levels of radiation pattern were lower than −21 dB at the boresights and the beam width of radiation patterns at E-plane and H-plane were more than 70° for two polarization ports. The designed antenna in this paper was fabricated and measured. The measurement results indicated that the designed antenna achieved anticipated radiation performances and design effectiveness of the dual-polarized antenna in this paper was proved. The dual-polarized and cylindrical waveguide antenna is suitable for some application fields such as dual-polarized array radar. The research results in this paper can provide a technical basis for the practical engineering application.     

Electromagnetic scattering from a dielectric cylinder buried beneath a slightly rough surface

An analytical solution is presented for the electromagnetic scattering from a dielectric circular cylinder embedded in a dielectric half-space with a slightly rough interface. The solution utilizes the spectral (plane-wave) representation of the fields and accounts for all the multiple interactions between the rough interface and the. buried cylinder. First-order coefficients from the small perturbation method are used for computation of the scattered fields from the rough surface. The derivation includes both TM and TE polarizations and can be easily extended for other cylindrical buried objects (e.g., cylindrical shell, metallic cylinder). Several scattering scenarios are examined utilizing the new solution for a dielectric cylinder beneath a flat, sinusoidal, and arbitrary rough surface profile. Results indicate that the scattering pattern of a buried object below a slightly rough surface differs from the flat surface case only when the surface roughness spectrum contains a limited range of spatial frequencies. Furthermore, the illuminated area of the incident wave is seen to be a critical factor in the visibility of a buried object below a rough surface.     

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     

Theoretical study of magnetic field of current monopoles in specialvolume conductor using symmetry analysis

The authors derive a formula for the magnetic field outside volume conductors having axial symmetry with radial and axial symmetrically distributed source currents. The magnetic field is shown to have components only along the cylindrical polar angle direction and its magnitude to depend only on the topological structure of the volume conductor and the location of the source current. With this formula, the magnetic field generated by the volume current of a current monopole within and on the symmetrical axis of several volume conductors (such as semi-infinite volume, infinite slab, sphere, infinite cylinder, semi-infinite cylinder, finite cylinder, prolate spheroid, and oblate spheroid) is shown to be equivalent to the magnetic field generated by a line current calculated using the Biot-Savart's law. In the first three volume conductors, the monopole solution of the magnetic field allows the calculation of magnetic fields generated by arbitrarily distributed (and balanced for finite volume conductors) current monopoles