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In this paper, the electromagnetic field of electrically large circular loop antennas, with different radii and different nonuniform current values, around a dielectric coated conducting sphere is considered. One or more loop antennas are located on the outer surface of a spherical dielectric shell covering a conducting sphere. Eigenfunction series solutions for the field are assumed in two regions. The current distribution on the wire loop, driven by a voltage source, is determined by Fourier series expansion and all necessary harmonics are taken into account. Exact analytical field expressions in closed forms are derived and field patterns are plotted. The antenna model and formulation presented in this paper offer exact analytical solutions to several loop antenna problems. Index Terms--Conducting bodies, dielectric bodies, loop antennas, nonuniform current, radiation.

A method of moments (MoM) solution is presented for the problem of electromagnetic scattering by a three-dimensional (3-D) inhomogeneous chiral scatterer illuminated by an arbitrary incident field. The volume equivalence principle was used to obtain coupled integral equations for equivalent volume currents. These integral equations were then solved numerically using MoM. The volume of the scatterer was modeled by tetrahedral cells, and face-based expansion functions were used to approximate the equivalent currents. Computed results are in very good agreement with exact data or other published data. Index Terms--Chiral scatterer, face-based expansion functions, method of moments (MoM), tetrahedral mesh, volume formulation.

The problem of electromagnetic scattering from an arbitrary homogeneous chiral body of revolution is formulated using the surface equivalence principle and is solved numerically by the method of moments. The numerical solution is implemented by means of a general computer program written for chiral bodies of revolution. Numerical results are given for bistatic radar cross sections of a chiral sphere. These results agree well with exact results obtained by the eigenfunction solution. Index Terms--Author, please supply your own keywords or send a blank e-mail to keywords@ieee.org to receive a list of suggested keywords.

A study of electromagnetic resonances of an isotropic chiral sphere is presented. The characteristic equation of a chiral sphere, which is complex and transcendental, is obtained by forming solutions of the electromagnetic field for a chiral sphere in terms of the spherical vector wave functions. The characteristic equation is solved by using a computer. Resonant frequencies and Q factors of the first few modes for relative permittivities of two and ten are reported and discussed. These modes are hybrid modes. They are classed as either hybrid electric (HE) modes or hybrid magnetic (HM) modes. Chirality is observed to have a significant effect on the resonances of a sphere. Index Terms--Chiral media, chiral sphere, Q factor, resonance.

The method of moments technique for analyzing electromagnetic scattering from an arbitrarily shaped three-dimensional homogeneous chiral body is presented based on the combined field integral equations. The body is assumed to be illuminated by a plane wave. The surface equivalence principle is used to replace the body by equivalent electric and magnetic surface currents. These currents radiating in unbounded free space produce the correct scattered field outside. The negatives of these currents produce the correct total internal field, when radiating in an unbounded chiral medium. By enforcing the continuity of the tangential components of the total electric and magnetic fields on the surface of the body, a set of coupled integral equations is obtained for the equivalent surface currents. The surface of the body is modeled using triangular patches. The triangular rooftop vector expansion functions are used for both equivalent surface currents. The coefficients of these expansion functions are obtained using the method of moments. The mixed potential formulation for a chiral medium is developed and used to obtain explicit expressions for the electric and magnetic fields produced by surface currents. Numerical results for bistatic radar cross sections are presented for three chiral scatterers--a sphere, a finite circular cylinder, and a cube. Index Terms--Chiral media, electromagnetic scattering, integral equations, method of moments.

Heretofore, the electromagnetic field produced by a specified tangential electric field in an aperture in the wall of an arbitrarily shaped cavity has most often been expanded in terms of cavity modes. An alternative approach, that of the electric field integral equation is presented. In this approach, the cavity field is expressed as the field of a surface density of tangential electric current, or a surface density of tangential magnetic current, or a combination of surface densities of tangential electric and magnetic currents on the boundary of the cavity. Each surface density is characterized by a single tangential vector function which is determined by the integral equation requiring that the part of the electric field tangent to the boundary of the cavity must reduce to the specified tangential electric field in the aperture and zero elsewhere on the boundary of the cavity. The electric field integral equation method is specialized to more easily determine the field inside an arbitrary cylindrical cavity excited by a tangential electric field in an aperture in its lateral wall. The method is further specialized to a circular cavity.

The reaction R([J.sub.1],[J.sub.2]) between two electric surface current densities [J.sub.1] and [J.sub.2] is the integral of the dot product of [J.sub.1] with the electric field produced by [J.sub.2]. Jack H. Richmond has correctly shown that the reaction is variational (a formula is variational if it has a stationary point at the quantity of interest) with Galerkin's method but is not necessarily variational when the non-Galerkin moment method is applied in the manner where one set of functions is used to expand both [J.sub.1] and [J.sub.2] and another set of functions is used to test both the integral equation for [J.sub.1] and that for [J.sub.2]. In this paper, the reaction R([J.sub.1],[J.sub.2]) is shown to be variational when the non-Galerkin method is applied in the manner of operation where the set of functions used to expand [J.sub.2] is the set of functions used to test the integral equation for [J.sub.1] and the set of functions used to test the integral equation for [J.sub.2] is the set of functions used to expand [J.sub.1]. Hence, the manner of operation just described may be more appropriate than Richmond's if a variational result is desired. A few numerical results are included to compare the performance of both manners of operation.

The electromagnetic coupling of an incident plane wave through a wire-penetrated electrically small aperture in an infinite conducting screen is considered. An equivalent-circuit model for the analysis of the wire-aperture coupling is developed by use of Norton's equivalence theorem. The method of moments is employed to find the equivalent network parameters in the model. Numerical results are presented for several cases of interest.

A method to evaluate the second normal partial derivative of the integral of the Green's function is presented in this short paper. Such a derivative appears in the solution of aperture problems in electrostatics. When computing the self-elements of the moment matrix, interchanging the order of differentiation and integration leads to integrals that are very unstable numerically and hence undesirable. This is due to the fact that these integrals grow in proportion to the reciprocal of the radius of the circle deleted around the singularity. In this paper, we present a method to avoid this difficulty for triangular patches. Plane triangular patches were chosen for their usefulness and popularity for arbitrarily shaped apertures. The theory is applicable to other surfaces of interest, such as polygons. The results obtained are simple and very convenient for numerical purposes.

The problem of electromagnetic radiation from a circular loop antenna of radius a, carrying a current I is considered. The loop may be radiating in the presence of one or more of the following objects: a centrally located dielectric or perfectly conducting sphere of radius b [is less than] a, a spherical dielectric shell of inner radius c [is greater than] a and outer radius d, a perfectly conducting spherically symmetric cap at radius b, and another such cap at radius d. Typical geometric structures considered are shown in Fig. 1. It is demonstrated how the presence of the sphere, shell, and caps can change and direct the radiation pattern of the loop. Index Terms--Circular loop, dielectric bodies, loop antennas, radomes, spheres, spherical antennas.

Dielectric filters can provide compact solutions for filter design problems. However, most dielectrics exhibit uniaxial properties, as well as, losses that will undoubtedly affect performance if not accounted for. This paper derives dispersion relations for lossy uniaxial media in dielectric waveguides and also accounts for lossy conducting walls. The waveguide discontinuity problem in the presence of lossy uniaxial media and finite conductivity waveguide walls, is calculated by mode matching technique and the results are applied to a Ka band filter. The design specifications for the proposed filter are a 32.5 GHz center frequency with 6%. Good agreement between simulated and measured results are shown. [ABSTRACT FROM AUTHOR]