摘要:

The theory of Lie algebras and their classification based on Dynkin diagrams is reviewed and application of the theory to vector wave scattering and propagation is outlined. The main applications arise through the matrix exponential function and associated matrix representations for the underlying groups. By projecting experimental measurements onto the eigenvectors of these basis elements, clear physical significance may be attached to the propagation operators. A new method for dealing with partially coherent propagators is outlined and an example for backscatter from a cloud of dipoles is used to illustrate the technique.

ISSN:0920-5071    

DOI:10.1163/156939392X00445

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A definitive method for the calculation of the bistatic radar scattering cross section of a cloud of randomly oriented conducting wire dipoles has been developed by Dedrick et al. [6]. It is based on a Stokes parameter formalism, thus containing complete information regarding transmitter and receiver polarizations. Since the single-wire cross section exhibits strong resonance effects, it is of interest to investigate to what extent these resonance phenomena are affected by the orientation average in a cloud of randomly oriented wires. To study this question, we present comprehensive three-dimensional graphs of the relevant bistatic cross sections plotted versus scattering angle and frequency, as well as of the various polarization functions, using the Einarsson wire cross section. The results indicate the degree to which the resonance features persist in both cross section and polarizations after orientation averaging.

ISSN:0920-5071    

DOI:10.1163/156939392X00454

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The calculation of the transient voltage and current along a nonuniform LCRG transmission line of finite length is considered. The model equations form a system of first order coupled differential equations for the voltage and current, and it is solved by a combination of a wave splitting technique and an invariant imbedding approach as well as a Green's functions approach. Partial differential equations for the reflection kernel, transmission kernel and the Green's functions are derived. Results from two different types of splittings are compared. Numerical results for the direct and also for particular inverse problems are presented. Finally it is noted that the system of equations obtained in a special case corresponds to Maxwell's equations for plane wave propagation in a slab where the permittivity, conductivity, and permeability vary with the depth.

ISSN:0920-5071    

DOI:10.1163/156939392X00463

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

In a dense discrete random medium, the propagation and scattering of waves are affected by the statistics of the particle positions. For the case of particles of finite size, the positions of the particles relative to each other in the presence of other particles are correlated and the second order statistics are described by the pair distribution functions. In this paper, we perform Monte Carlo simulations of pair distribution functions of dense discrete random media consisting of particles of multiple sizes. The Metropolis technique and the sequential random addition of particles methods are used to generate a series of configurations through random processes. The pair distribution functions are calculated by counting the average occurrence of pair separation of particles. The Monte Carlo results of the particle pair distribution functions are illustrated and are compared with the results of the Percus-Yevick approximation. The results from the two Monte Carlo methods are found to be in good agreement.

ISSN:0920-5071    

DOI:10.1163/156939392X00472

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Methods due to Gurtin and Ainola are used to extend the well-known Stratton-Chu formulae in electromagnetic theory to the initial value problem. A suitable Green's Function is obtained, and a variational principle is posed which generates the equations governing the electric and magnetic fields.

ISSN:0920-5071    

DOI:10.1163/156939392X00481

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The paper summarizes results of original researches on microwave remote sensing of vegetation conducted at the Institute of Radioengineering and Electronics of the AS, USSR during the last years. Vegetation models as continuous and discrete media are analyzed. The discrete approach appears to be more adequate for the description of microwave propagation in vegetation. Microwave scattering and absorption by plant elements of different shapes and sizes are studied. It allows one to obtain the relation between electrodynamic and biometric parameters of vegetation canopies. It is shown that microwave attenuation for given wavelength and vegetation type is defined by the canopy water content per unit area, the relative volume density of vegetation and the moisture of plant elements. The radiation model of vegetation canopy is proposed as a closed system of equations for the emissivity and the backscattering coefficient. Experiments measuring attenuation and emission properties of vegetation were perfomed under laboratory conditions as well under natural conditions with moving platforms and aircrafts. The developed models are in a good agreement with experimental data.

ISSN:0920-5071    

DOI:10.1163/156939392X00490

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Coded passive transponder cards are proposed for the detection and localization of underground cooperative objects. The detection system active transmitter antenna polarization, gain and beam grazing angles are investigated to achieve maximum energy transmission to ground and to the passive transponder cards connected to the objects to be detected and localized. The detection probability can be significantly enhanced by applying space and polarization diversity of two transponder cards with two orthogonal polarized antennae on each cooperative object. Methods are suggested for improving the performances and the reliability of the objects detection and localization systems.

ISSN:0920-5071    

DOI:10.1163/156939392X00508

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The concept, that leaky waves may grow with increasing depth in a conducting half-space, is explored. The subject is introduced by considering an infinitely extended aperture where, in principle, a growing wave can be produced, with a special form of traveling wave excitation. We then enquire if a finite rectangular aperture cannot excite a wave which grows with depth in the conductor. The results obtained show this is indeed possible over a limited near-field region.

ISSN:0920-5071    

DOI:10.1163/156939392X00517

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939392X00526

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor