J. Richmond

Scattering by a dielectric cylinder of arbitrary cross section shape

The theory and equations are developed for the scattering pattern of a dielectric cylinder of arbitrary cross section shape. The harmonic incident wave is assumed to have its electric vector parallel with the axis of the cylinder, and the field intensities are assumed to be independent of distance along the axis. Solutions are readily obtained for inhomogeneous cylinders when the permittivity is independent of distance along the cylinder axis. Although other investigators have approximated the field within the dielectric body by the incident field, we treat the total field as an unknown function which is determined by solving a system of linear equations. In the case of the dielectric cylindrical shell of circular cross section, this technique yields results which agree accurately with the exact classical solution. Scattering patterns are also presented in graphical form for a dielectric shell of semicircular cross section, a thin homogeneous plane dielectric sheet of finite width, and an inhomogeneous plane sheet. The effects of surface-wave excitation and mutual interaction among the various portions of the dielectric shell are included automatically in this solutiom

TE-wave scattering by a dielectric cylinder of arbitrary cross-section shape

The theory and equations are developed for the scattering pattern of a dielectric cylinder of infinite length and arbitrary cross-section shape. The harmonic incident wave is assumed to have its electric vector perpendicular to the axis of the cylinder, and the fields are assumed to have no variations along this axis. Although some investigators have approximated the field within the dielectric body by the incident field, a more accurate solution is obtained here by treating the field as an unknown function which is determined by solving a system of linear equations. Scattering patterns obtained by this method are presented for dielectric shells of circular and semicircular cross section, and for a thin plane dielectric slab of finite width. The results for the circular shell agree accurately with the exact classical solution. The effects of surface-wave excitation and mutual interaction among the various portions of the shell are included automatically in this solution.

A wire-grid model for scattering by conducting bodies

A point-matching solution is developed for scattering by conducting bodies of arbitrary shape. Numerical results are included for the backscatter echo area of circular and square wire loops, circular and square plates, spheres, and hemispheres. The results show good agreement with experimental data. An efficient calculation procedure is achieved by using a wire-grid model instead of a continuous conducting surface. A system of linear equations is generated by enforcing the boundary conditions at the center of each wire segment of the grid, and a digital computer is employed to solve these equations for the currents on the segments. Then it is straightforward to calculate the distant scattered field and the echo area.

Mutual impedance of nonplanar-skew sinusoidal dipoles

The mutual impedance of nonplanar-skew sinusoidal dipoles is presented rigorously as a summation of several exponential integrals with complex arguments.

A reaction theorem and its application to antenna impedance calculations

The reaction theorem is generalized to allow the fields of an antenna in one environment to be employed in calculations of mutual impedance in another environment. Several expressions for self-impedance and mutual impedance are presented. These are in the form of surface integrals or volume integrals of the field intensities or the current density. It is shown how the fields of an antenna in free space can be useful in calculating the impedance in the presence of scatterers.

On the edge mode in the theory of TM scattering by a strip or strip grating

Consider a plane wave incident on a perfectly conducting strip (or strip grating), and let the incident electric vector be parallel with the edges of the strip. If the edge mode is included among the basis functions, it is found this greatly improves the convergence of the moment-method solution. Numerical data are included for the reflection coefficient of the strip grating. To correct an error in the previous literature, the rigorous solution is tabulated for broadside backscatter from a single strip.

Mutual impedance between coplanar-skew dipoles

The induced EMF formulation is employed to develop a closed-form expression for the mutual impedance between coplanar-skew dipoles, Numerical results are presented in graphical form.

Axial slot antenna on dielectric-coated elliptic cylinder

The radiation properties of an axial slot antenna on a conducting elliptic cylinder with a homogeneous dielectric coating are investigated. In the dielectric coating and in the exterior free-space region the field is expanded in elliptic waves using the Mathieu functions. The Mathieu angular functions are employed as basis and testing functions to enforce the boundary conditions at the interface between the dielectric and the free-space regions. The equations of continuity at the boundary are solved by Galerkins method. Numerical results are presented in graphical form for the transverse electric (TE) and transverse magnetic (TM) polarizations to illustrate the far-field radiation patterns, the gain versus coating thickness, and the aperture conductance versus coating thickness. >

Scattering by thin dielectric strips

A plane wave incident on a thin dielectric strip with infinite length is considered, letting the incident electric field vector be parallel with the edges of the strip. The field is expanded in the dielectric region as the sum of three plane waves (the forced wave and two surface waves). The x -axis and y -axis propagation constants are known for each wave, and Galerkins method is employed to determine the amplitudes of these waves. Finally, the far-zone scattered field is determined by considering the polarization currents radiating in free space. Numerical data are presented to illustrate the scattering properties of lossless and lossy dielectric strips as a function of the angle of incidence and the width of the strip. The calculations show excellent agreement with an earlier moment method using pulse bases and point matching.

Monopole antenna on circular disk

The sinusoidal-Galerkin moment method is developed for the impedance of a monopole antenna at the center of a circular disk in free space. Numerical results are presented for the impedance and current distributions as a function of the disk radius.