摘要:

The Mode Matching Technique is employed for the evaluation of the Radar Cross-Section (RCS) of cylindrical inlets terminated by a perfectly conducting cylindrical hub or a cylindrical array of grooves that may be straight or curved. In the case of curved grooves, the geometry is analyzed via the generalized transmission line theory and a closed form solution is given for the first time. The method is formally exact, and yields accurate RCS patterns for geometries that have not been previously investigated. Analytical expressions are derived for the coupling factors between the various modes and RCS results are presented which may be used as a reference in validating other, more general numerical techniques.

ISSN:0920-5071    

DOI:10.1163/156939395X00118

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A new version of nonstationary radiative transfer theory for vector electromagnetic wave multiple scattering in a discrete random medium is presented in which the electromagnetic energy within dielectric scatterers may be large. The starting point is the general two frequency Bethe-Salpeter equation for the coherence tensor-function of the wave electric field. In the two frequency domain it is proved that the Poynting's theorem can be decomposed into (1) a theorem for the spectral component of the electric energy density multiplied by two and (2) a theorem for the difference between the spectral components of the electric and the magnetic energy densities. The Poynting's theorem is closely connected with a generalized two-frequency Ward-Takahashi identity according to which the extinction of a nonsteady radiation is conditioned by the incoherent scattering, the real absorption and changing of the energy accumulation inside scatterers. As result a new radiative transfer equation is obtained for the radiance tensor of a pulse radiation in unbounded random medium. This equation differs from the traditional one by a term with the time derivative where the inverse value of the group velocity is replaced by a tensor-operator which determines the average rate of the electromagnetic energy change within scatterers.

ISSN:0920-5071    

DOI:10.1163/156939395X00127

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The electromagnetic field problem for general, linear, homogeneous bianisotropic media is studied for field dependence on one spatial coordinate only. Explicit solutions for the dyadic Green functions are presented, first in general, then with special emphasis on transverse bianisotropy and biaxiality. The results are amenable to straightforward numerical implementation. They will mostly serve for a better understanding of the wealth of electromagnetic phenomena in complex materials and complement experimental studies in appropriate restricted configurations.

ISSN:0920-5071    

DOI:10.1163/156939395X00136

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The results of cylindrical F-Layer model [1] are generalized for the case of a flat-layer of an inhomogeneous, magnetized plasma, which seems to be more adequate for describing the Earth's ionospheric F-Layer. Two opposite models are considered: a plasma layer with sharp boundaries and an inhomogeneous plasma layer with smooth plasma density profile. The mechanism of whistlers absorption due to oblique Langmuir waves excitation or their emission outside the F-Layer is discussed. It is shown that this mechanism may be important only in the model of plasma layer with sharp boundaries.

ISSN:0920-5071    

DOI:10.1163/156939395X00145

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The impedance per unit length is considered in situations where rectangular conductors are in close proximity (the geometry considered is that of a narrow slot with depth). Application of the previously derived right angle corner constant, when the conductors are far apart compared to the electrical scales of length (such as skin depth), is modified to account for proximity effects. Alternatively, when the conductors are close together compared to the electrical scales of length, the gap region is eliminated and the fields are induced by appropriate fictitious sources at the gap location. The local impedance per unit length is thus determined and various limiting cases of the conductor thickness (or depth) are considered. A comparison with the thin shell impedance approximation is also made.

ISSN:0920-5071    

DOI:10.1163/156939395X00154

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

This paper deals with the electromagnetic field backscattered by a chiral object when illuminated by a linearly polarized plane wave. Computer simulations are carried out using four different computer codes, three of them based on a surface integral equation method using bidimensional finite elements for solving the scattering problem. The various shapes we consider are one- or three-turn regular helices, canonical helices, patterns appearing in pseudo-chiral or omega media, as well as non-chiral shapes such as wires and a loop studied for comparison purposes. They are mostly perfectly conducting, but the case of low and high permittivity dielectrics has also been treated. These objects can be embedded either in free-space or in a (lossy) dielectric medium. A first stage is devoted to the comparison of results given by the various computer codes for a three-turn regular helix and a canonical helix. For the latter, comparison with measurements will also be reported. Then, the far field responses of the various shapes are compared with one another for several incidences and polarizations of the incident field. The influence of the host medium and the nature of the target material are also mentioned for the particular case of a three-turn regular helix. Finally, we indicate how these results could be used in the field of chiral composites modeling.

ISSN:0920-5071    

DOI:10.1163/156939395X00163

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A new method for scattering from radially inhomogeneous cylinders of large radius is presented herein. It is based on the Coupled Azimuthal Potentials (CAP) Formulation [1], i.e., a description of the fields in terms of magnetic and electric azimuthal potentials. Since the cylinders considered are in 2D geometry of revolution, they are split in concentric layers where the Gaussian profile of the permittivity is approached by a piecewise constant function. The novelty of the method is to solve directly Maxwell's equations for a permittivity varying continuously radially, in terms of modal tangential electromagnetic fields, by making the steplength of the layers tend to zero. This allows us to minimize the size of linear systems. Properties of the potentials are used only on the cylinder axis and at infinity. The potential coefficients are developed by using cylindrical functions to express the boundary conditions. Then, asymptotic approximations are used to determine the diffracted fields at infinity. Numerical results of near-field map are compared with others obtained via the Finite Element Method codes. But these codes require quite small meshes and are thus limited in size of geometry. Moreover, polarized and depolarized scattering widths are presented which show the depolarization of the diffracted field for both TE and TM polarizations of the incident field. It is revealed that the fields are noticeably modified by the medium and that the angle of incidence has a great influence on the levels of scattering width.

ISSN:0920-5071    

DOI:10.1163/156939395X00172

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Coupling between the two degenerate modes of a square patch, caused by a square corner cutout, is examined. The effect of a corner cutout on the coupling between modes of two adjacent patches is also discussed. The problem is formulated using an integral equation in the spectral domain, and solved with the Method of Moments. Two types of basis functions were used; full domain functions, with the edge condition, and subdomain basis functions. Placement of basis functions around the corner cutout is discussed. Results are presented showing the coupling between modes on a single patch, coupling between the modes on adjacent patches, and the effects of gap coupling the patch to a 50 ohm feedline.

ISSN:0920-5071    

DOI:10.1163/156939395X00181

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939395X00190

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939395X00208

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor