摘要:

Two techniques of simultaneous measurement of source direction and polarization, using three orthogonal short dipoles, are reviewed and extended to cover partially polarized waves. One technique involves forming the real part of the 3 x 3 antenna voltage coherency matrix. The other involves forming the imaginary part of the same matrix. The concept of a transfer function matrix for an arbitrary three-port antenna is then developed. This concept allows the source direction and polarization to be measured simultaneously, using an iterative method, when antennas other than short dipoles are used. The method involves transformation of the transfer function matrix among various reference frames. A novel polarization transform is then developed which greatly improves the convergence properties of the iterative method, and which permits the wave parameters to be determined even when the waves are linearly polarized. The method requires that both the real and imaginary parts of the antenna voltage coherency matrix are formed. The method is valid for partially polarized and unpolarized waves in addition to purely polarized waves. An example, which has been simulated numerically, is also presented.

ISSN:0920-5071    

DOI:10.1163/156939391X00257

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We formulate the general waveguide discontinuity problem in terms of reflection and transmission operators using a general mode-matching method. This allows the multidiscontinuity problem for arbitrarily shaped waveguides to be solved easily. We then relate the mode-matching method to the integral equation method by using the equivalence principle. This sheds light on the issue of relative convergence. We prescribe a more relaxed condition for obtaining a convergent solution to this problem. The idea is illustrated by a numerical simulation.

ISSN:0920-5071    

DOI:10.1163/156939391X00266

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A formulation based on the finite element method and the periodic boundary condition for plane wave scattering by rough surfaces is derived and implemented. The method is applied to Monte Carlo simulations of one-dimensional random rough surface scattering with a Gaussian roughness spectrum satisfying Dirichlet boundary conditions. Convergence of the method is demonstrated by varying the number of sampling points. The percent error in conservation of energy is shown to be less than 0.007% for all the examples presented. The numerical solutions are compared with integral equation methods. The results from the finite element method are in perfect numerical agreement with the integral equation results for each surface realization if the periodic boundary condition is also used in the integral equation method. They are in excellent numerical agreement with a tapered wave solution of the integral equation for large surface lengths and upon averaging over many realizations. For the examples discussed, it is shown that the CPU time and memory storage requirements for the finite element method are much less than those of the integral equation method for cases when the number of horizontal sampling points is much larger than the number of vertical points in the region of discretization. Numerical results are presented for various rms surface heights, correlation lengths and surface lengths. The results are also shown to be consistent with the corresponding Kirchhoff approximation and the small perturbation theory within the domains of validity of the two approximate methods.

ISSN:0920-5071    

DOI:10.1163/156939391X00275

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The WKB method and its generalization, well known to be applicable to a certain class of achiral isotropic inhomogeneous media, are extended to stratified chiral media for waves with normal incidence. The method is based on an expansion in wave fields, certain combinations of the electric and magnetic fields, whose properties are also extensively studied in the paper. It is seen that for sufficiently slowly varying media, the reflection dyadic due to the stratification can be expressed in closed integral form and, for normal incidence, the result is independent of the chirality parameter κ applied in this paper. The method can be further extended for chiral media to what is known as the Bremmer series method for achiral media.

ISSN:0920-5071    

DOI:10.1163/156939391X00284

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

We investigated the diffusive reflection of electromagnetic waves from a slightly rough impedance surface separating vacuum and dielectric media with a large positive real part of the dielectric constant. The essential peculiarity of this case is the absence of surface waves on the plane surface. Nevertheless, backscattering enhancement takes part in this case also: the calculated scattering indicatrix has a peak in the direction opposite to the wavevector of the incident wave.

ISSN:0920-5071    

DOI:10.1163/156939391X00293

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Thermal emission (brightness temperature) from a multi-layered medium with different temperature profiles is obtained. The analysis proceeds by writing the radiative transfer equation in each layer. Relating the intensities at the interfaces through the boundary conditions leads to the propagation matrices. As an application, the brightness temperature from a human tissue composed of skin, fat, and muscle is obtained. The method discussed is applicable for determining uniform and nonuniform temperature profiles.

ISSN:0920-5071    

DOI:10.1163/156939391X00301

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

The average field of an electrical dipole of arbitrary orientation, placed over a statistically rough sphere with a small surface impedance, is analyzed using Bourret's approximation. The isotropic and statistically uniform inhomogeneities are assumed to be small and smooth, which allows the use of a perturbation theory in the boundary conditions. Effective reflection coefficients for spherical waves are calculated, the analytical properties of which allow application of the Watson method for an asymptotic analysis of the average field in the illuminated region and in the shadow.

ISSN:0920-5071    

DOI:10.1163/156939391X00310

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939391X00329

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939391X00338

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor