摘要:

A numerical solution to an integral equation is developed (via the moment method) for the current induced on an axially-directed antenna in the presence of an infinitely long, perfectly conducting tube where the antenna can be either inside or outside the tube. The special case of a cylindrical antenna residing coaxially within the conducting tube is treated as is the more general off-axis case. The salient properties of the part of the integral equation kernel due to the presence of the infinite tube are highlighted since this term contains an infinite series of Sommerfeld-type integrals with complicated integrands. Attention is given to the efficient numerical evaluation of this term in light of the various singularities which exist on the path along which the integral is evaluated. Techniques which accelerate the convergence of the series are presented for the case where the antenna is very near the tube's surface. Data for the current induced on the antenna are presented for various cases where the antenna is inside or outside the tube.

ISSN:0920-5071    

DOI:10.1163/156939393X00958

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The polarimetric signature of the sea surface is calculated, by using the small perturbation method, from a two-scale sea surface model. This signature is formalized by the Mueller matrix, whose coefficients are functions of the speed of the wind, the incidence of illumination and the azimuthal direction of the wave with respect to the direction of the wind. The polarimetric signature of the ocean is then described by the nine Huynen coefficients. In this paper, the cross-correlation between these coefficients is shown; a reduction of the polarimetric information to a Huynen vector whose dimension is minimal (five) is proposed. From this defined vector a Bayesian estimator (a maximum likelihood ratio test) is built, making it possible to estimate the wind direction and speed from polarimetric measurements of the sea backscattering.

ISSN:0920-5071    

DOI:10.1163/156939393X00967

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

An inverse scattering model based on an artificial neural network using the back-error propagation technique is presented in this paper. The vegetation canopy is modelled as a half-space of randomly distributed and orientated circular disks, representing the leaves. A Monte Carlo model is used as the forward scattering model to calculate the radar backscatter coefficients. Using different sets of input parameters such as leaf moisture content, frequency and size of leaf, this forward model generates about 2000 sets of backscatter coefficients. These sets of backscatter coefficients and the corresponding input parameters form a training set for the neural network. The trained neural network constitutes an inverse scatter model. Given a set of backscatter coefficients, our model is able to estimate simultaneously the leaf moisture content, the radius and the thickness of the circular leaf within an accuracy of 10%.

ISSN:0920-5071    

DOI:10.1163/156939393X00976

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

A simple volume and surface formulation is presented to analyze the problem of scattering of TE waves by multiple perfectly conducting and dielectric cylinders of arbitrary cross section. The Method of Moments and the principle of equivalence are used to replace the cylinders by equivalent surface and volume currents radiating in an unbounded medium. The surface currents are obtained by enforcing the boundary conditions on the surface of the conducting cylinders, and the volume currents are obtained by applying the equivalence principle inside the volume of the material cylinders. This procedure leads to integral equations for the currents in each of the cylinders considered. The Method of Moments is used to solve the integral equations. Triangular functions are used to expand the surface currents on the conducting cylinders and a set of volume solenoidal basis functions is used to expand the volume currents in the dielectric cylinders. Some of the deficiencies of the formulation are discussed. Results are presented showing that the formulation is in good agreement with other available published data.

ISSN:0920-5071    

DOI:10.1163/156939393X00985

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

For a waveguide consisting of multiple layers of dielectric material, a mode eigenfunction of the waveguide can be computed either from the outer-most layer inward or from the inner-most layer outward once the guide wavenumber is known. The guidance condition requires that the eigenfunction of a mode is independent of these two different computation procedures. This requirement can be used for checking the accuracy of numerical computation. When significant discrepancies between these two procedures were observed during a recent revision of a waveguide mode based tropospheric propagation program, it was found that one of the two procedures converged to the mode eigenfunction much faster. This consistency condition has been utilized successfully to relax the requirement on eigenvalue accuracy by identifying the procedure which converges to the correct mode eigenfunction faster.

ISSN:0920-5071    

DOI:10.1163/156939393X00994

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The radiation properties of a microstrip disk resonator excited by a cylindrical line probe is investigated analytically. A mixed spectrum eigenwave expansion is employed to describe the electromagnetic fields below and above the microstrip resonator. A voltage gap generator model is used to take into account the excitation of the radiation structure. An integral equation is obtained on the semi-infinite cylinder encircling the microstrip disk with the unknown term being the vertical component of the aperture electric field. The integral equation is solved by applying an iterative procedure, where the magnetic-walls solution is employed as the initial approximation. Then, the input impedance of the microstrip disk is determined by computing the total current at the feeding point. Radiation patterns are also computed and presented.

ISSN:0920-5071    

DOI:10.1163/156939393X01001

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

In this paper we propose a 3-D imaging method combining the concepts of monopulse imaging and wideband ISAR imaging. The field backscattered from a rotating object is received by two vertically-displaced antennas. From the fields received by the two antennas we can obtain a 3-D image which provides information about scattering strength and the 3-D position parameters (down range, cross range, and height) of the object's scattering centers. This method does not unduly increase the complexity of the data acquisition or computing load in the image reconstruction. Numerical and experimental results show the effectiveness of the proposed method. However, when multiple scattering centers are collocated at the same projective coordinate with different height, the proposed method fails to separate the scatterers.

ISSN:0920-5071    

DOI:10.1163/156939393X01010

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939393X01029

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939393X01038

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor