摘要:

The random medium model has been used quite successfully in the interpretation of active and passive microwave remote sensing data from earth terrain. In the random medium model, a correlation function with associated mean and variance is used to describe the random permittivity fluctuations. Most of the correlation functions used, thus far, in the random medium model have been of exponential form, or of other simple expressions derived from physical arguments. In this paper, we calculate the correlation function for a specific physical model of the random medium which is a random collection of discrete scatterers imbedded in a background medium of constant permittivity. Correlation functions are calculated for impenetrable and penetrable spherical scatterers. Once the correlation function is obtained, the strong fluctuation theory is used to calculate the effective permittivity. Then, the distorted Born approximation is used to calculate backscattering coefficients for a halfspace configuration. Theoretical results are illustrated by comparing effective permittivities and backscattering coefficients obtained from the penetrable and impenetrable models.

ISSN:0920-5071    

DOI:10.1163/156939394X00597

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A new algorithm is developed to evaluate the responses of discontinuous coplanar striplines excited by external electromagnetic fields. The algorithm uses the cascade chain matrix method which employs the distributed circuit parameters to model the external field coupling and it is applicable to most commonly encountered discontinuities in microwave integrated circuit interconnects on lossy substrates. A general CAD program is developed based on this model and it is applied to realistic coplanar line interconnections with geometric and resistive discontinuities to illustrate the capabilities of the algorithm. These interconnect models are selected from a practical microwave integrated circuit design. Simplicity and fast speed of the algorithm enable computer aided analysis of externally induced electromagnetic noise in integrated circuits to be carried out.

ISSN:0920-5071    

DOI:10.1163/156939394X00605

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The dielectric zones of phase-correcting Fresnel-zone plate antennas are usually considered to be ideal phase-shifters. In this paper, we model the interaction between an incident electromagnetic wave and the dielectric material of such an antenna more accurately and present a new calculation method to obtain its far-field radiation pattern. A comparison between the patterns calculated following the new and the old approach demonstrates the necessity of using the new one.

ISSN:0920-5071    

DOI:10.1163/156939394X00614

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

We propose a simple approach to the evaluation of parameters of organic films on the sea surface from radar measurements. The approach is based on the perturbation technique for calculating the scattered field intensity and linear theory of water waves on the surface of a viscous fluid. As a result, we have obtained an evident expression for the intensity of the signal backscattered from the sea surface covered by a film, depending on the angle of incidence, surface tension, and elastic properties of the film. The obtained dependence is in qualitative agreement with the experimental data. The influence of the film on the Doppler shift of the scattered field frequency is also discussed.

ISSN:0920-5071    

DOI:10.1163/156939394X00623

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In this series of two papers, we consider in its maximum generality the problem of determining radiated electromagnetic fields starting from phaseless distributions on one or more surfaces surrounding the source. In this first part, theoretical aspects of the problem and the basic point of an appropriate formulation are examined. The problem is conveniently tackled as the inversion of the nonlinear, in particular 'quadratic', operator mapping the set of radiated fields into square amplitude distributions over prescribed surfaces. Next, the compactness property of the set of the unknown field is exploited, leading to an introduction of the finite dimensional representations for it and the concept of its "essential dimension". Furthermore, for the square amplitude data distributions finite dimensional representations are introduced and their "essential dimension" considered, also for more than one observation domain. Finally, due to the ill-posed nature of the problem, a generalized solution is defined as the global minimum of an appropriate functional and its existence discussed.

ISSN:0920-5071    

DOI:10.1163/156939394X00632

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

In this series of two papers we consider in its maximum generality the problem of determining electromagnetic fields starting from phaseless distributions on one or more surfaces. In this second part, novel uniqueness conditions for the solution of the problem, requiring in principle a single scanning surface, are introduced. Then, all questions related to the attainment of the generalized solution are discussed. The geometrical properties of the functional set corresponding to the range of the quadratic operator relating the unknowns to the data are examined. It is shown how to avoid both contingent local minima problems and ill-conditioning questions. The crucial role of the dimension of the data representation space is emphasized. The main benefits of the proposed approach are in the numerical search for the solution, that is the exact, closed form line search step in the minimization procedure and the introduction of a proper metric change in the functional, are stressed. A critical review of the results already obtained is performed with a particular care to the key points of the method.

ISSN:0920-5071    

DOI:10.1163/156939394X00641

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

An approximate procedure is proposed, to characterize the radiation from a class of open finite-length Wiener-Hopf (WH) structures, that is useful when a complete account of the direct feed radiation and of the open end effects is required, but the corresponding (exact) modified WH equation does not allow a closed-form evaluation. This procedure considers the finite-length problem as an appropriate superposition of two related semi-infinite WH problems, each one leading to an exact solution. It takes into consideration the discrete modes and the continuous spectrum waves launched at the feed end, and also at the structure open-end. The usefulness of this procedure is tested in the case of a finite-length multi-filar helix, fed by the open-end of a circular waveguide of the same diameter. Theoretical radiation patterns show a satisfactory agreement with experimental results.

ISSN:0920-5071    

DOI:10.1163/156939394X00650

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

The corner constant, which serves to correct the internal impedance per unit length of a conductor, is calculated in closed form for the limit of large ratios of internal to external magnetic permeabilities for a right angle comer. The solution is accomplished by means of a generalization of a method used in the problem of water waves on a sloping beach. The corner constant is determined by an integration of the surface axial electric field and the perfectly conducting magnetic field. Expansions of the axial electric field are also given because of its utility in future papers. The correct behavior of the surface magnetic field near the edge is determined by using the constant limit of the axial electric field in an internal Green's theorem representation. Rotation of the surface fields to a complex radial coordinate is discussed.

ISSN:0920-5071    

DOI:10.1163/156939394X00669

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939394X00678

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939394X00687

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor