摘要:

Radiation by directive sources over a rough planar surface is considered. It is shown that image theory can be used for computing the expected value of the scattered power density, in spite of the essentially incoherent nature of the scattering process, provided that a region of sufficient extent around the specular point, Fermat's region, is illuminated by the primary sources. This result resembles the case of reflection over a smooth plane; its mathematical derivation is also supported by a physical model.

ISSN:0920-5071    

DOI:10.1163/156939394X00696

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Investigation is conducted on the computational efficiency of van den Berg's integrated-squared-error algorithm with different variational basis functions (VBFs) when applied to dielectric problems. Members in this family include the Matrix interpretation of the Spectral Iteration Technique (MSIT) and the well-known Conjugate Gradient FFT (CGFFT)-each arises from choosing an appropriate form of the VBF. A third choice which is based on a generalized Neumann series (GNS) expansion of the inverse of the defining integral operator is shown to give much superior performance than either the MSIT or the CGFFT. Tests performed on a variety of object shapes and dielectric materials indicate that the GNS is the most efficient among all three FFT-based methods.

ISSN:0920-5071    

DOI:10.1163/156939394X00704

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The Born approximation is used to generate a sequence of iterates approximating spectral components of the continuous spectrum associated with longitudinally-uniform dielectric waveguides. Quantification of the electromagnetic fields within these structures is provided by an axial Fourier transform-domain electric field integral equation (EFIE) for the transverse components. Successive approximations of solutions to this EFIE for practical dielectric waveguiding structures are obtained. Convergence criteria of the Neumann series along with error estimates for each iterate are examined.

ISSN:0920-5071    

DOI:10.1163/156939394X00713

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This paper describes the activity performed in the framework of the 1990 AVIOSAR 580 SAR and scatterometer Italian campaign over the Matera test site. The experiment has been carried out to ascertain the reliability of surface scattering models in order to tackle with the data inversion problem. To achieve this goal, physical and geometrical features of 38 homogeneous bare soil fields are considered as a result of ground truth data collection. X band - VV polarization σ° values from the HUTSCAT scatterometer at 45° and from the CCRS airborne SAR sensor at the incidence angles between 50° and 62° are compared with those obtained from modeled data. The SAR data have been calibrated using both corner reflectors and extended natural targets. The backscatter variability due to surface roughness has been analyzed. Due to the characteristics of the analyzed data set, i.e., high incidence angle and surfaces with large root mean square slope profile m, the SPM and PO models were not suitable for many fields in the scene; on the other hand, a good agreement between theoretical predictions and experimental data is found when the Geometrical Optics (GO) model is used. A threshold value for m as function of the incidence angle is found and a physical interpretation of this behavior is also proposed. After the assessment of the GO model results, the problem of retrieving the real part of the soil relative dielectric constant Re(∈r) and m value is addressed as well, considering the extended Kalman filter approach. The comparison between the obtained values and the experimental data shows the reliability of the inversion approach, thus encouraging the use of more sophisticated backscattering models.

ISSN:0920-5071    

DOI:10.1163/156939394X00722

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

An integral equation for the right-angle finitely conducting corner is derived. A variational principle is used to construct an approximation for the corner constant; the value of the corner constant serves to correct the internal impedance per unit length of conductors when sharp comers are present. The external impedance solution is chosen as the tangential magnetic field trial function. Complex rotation of the radial coordinate in the variational expression is performed to reduce the calculation to numerical integration of a real quantity. A simple function is introduced to fit the calculated corner constant for general ratios of internal to external magnetic permeabilities.

ISSN:0920-5071    

DOI:10.1163/156939394X00731

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The transversely bianisotropic uniaxial medium, a generalization of the well-studied chiral material, can be fabricated by mixing metal helices in an isotropic host medium in such a way as to have the axes of all helices randomly oriented but perpendicular to a fixed direction. In the present consideration, based on the concept of characteristic waves and the method of angular spectral expansion, field representations in this class of medium are developed. The analysis reveals that the solutions of source-free Maxwell's equations for transversely bianisotropic uniaxial medium can be expressed in sum-integral forms of circular cylindrical vector wave functions. The addition theorem of vector wave functions for transversely bianisotropic uniaxial medium can be straightforwardly derived from that of vector wave functions for isotropic medium. Applications of the proposed theory to electromagnetic scattering are presented.

ISSN:0920-5071    

DOI:10.1163/156939394X00740

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

By means of known constitutive relations for the D and H fields, which include both electric quadrupole and magnetic dipole terms, an eigenvalue theory is developed for electromagnetic wave propagation in an absorbing chiral medium. The theory allows the polarization eigenvectors to be determined, which the medium supports, and also their refractive indices and absorption coefficients. Uniaxial and cubic crystals, as well as an ideal gas, are treated in this way, and expressions are derived for their circular birefringence and dichroism in terms of property tensors of the medium. These expressions are shown to be independent of the arbitrary origin to which the multipole moments are referred. The theory is also applicable to artificial chiral materials which are "optically active" in the microwave regime.

ISSN:0920-5071    

DOI:10.1163/156939394X00759

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939394X00768

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939394X00777

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor