摘要:

The corrugated pyramidal square horn with corrugations in the E-plane walls is investigated by means of Gaussian-Hermite beam mode analysis. The fractional power in the fundamental beam mode is about 98%. The near- and far-field radiation patterns are calculated by Gaussian-Hermite beam mode analysis. The latter is compared with the result obtained by conventional aperture field integration method, and good agreement is found. Finally, the accuracy of Gaussian beam mode analysis is discussed. The high fractional power in the fundamental beam mode of the horn indicates that it can be used as a high efficiency Gaussian beam launcher in quasi-optical systems.

ISSN:0920-5071    

DOI:10.1163/156939397X00116

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939397X00125

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The inverse scattering techniques have become widely used in many applications. These techniques are based on either continuous profile inversion or discrete multi-layer models. The FFT inversion method has been newly introduced for the detection of discrete multi-layer models. In this paper, the performance of the FFT inversion method is investigated for the case of band limited scattered field data. A modification of the inversion algorithm is presented to increase the accuracy of the method in this case. The proposed algorithm exhibits much better accuracy than the directly applied FFT inversion method.

ISSN:0920-5071    

DOI:10.1163/156939397X00134

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Theoretical expressions are presented for the illumination and phase efficiency of three types of Fresnel-zone plate antennas. Using these formulas, the bandwidths of the antennas will be analyzed and compared. Measured data are given to validate the theoretical results.

ISSN:0920-5071    

DOI:10.1163/156939397X00143

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Analytical expressions for the resonant frequencies of an electromagnetic rectangular/cylindrical/spherical cavity with an off-axis electrically small lossless dielectric sphere are obtained in a very simple and immediate manner, for both TE and TM modes. The walls of the cavities are perfectly conducting. Rectangular/cylindrical/spherical vector wave functions are used in our analysis. The results are useful for cavities containing small inhomogeneities, as well as for the determination of permittivities or permeabilities of various materials, from the measurement of the resonant frequency shifts caused by introducing small samples of them inside cavities.

ISSN:0920-5071    

DOI:10.1163/156939397X00152

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A state variable electromagnetic (EM) analysis technique called rigorous wave coupled theory (RCWT) (used for the EM and optical analysis of planar diffraction gratings) is applied to determine the radiation and scattering that arises from phi-periodic circular cylindrical dielectric systems which have arbitrary radial and azimuthal, inhomogeneous, permittivity variation. The RCWT state matrix equations and the associated boundary matrix equations (derived from a multi-layer cylindrical ladder analysis) are presented and solved for the cases: (1) when a plane wave (TM polarization, electric field parallel to the cylinder axis) is incident on the phi-periodic dielectric cylinder and (2) when an electric line current source excites EM radiation inside the phi-periodic dielectric cylinder. Numerical examples of plane wave scattering and line source radiation from phi-periodic dielectric cylinder systems are presented. Comparisons for the first time of scattering and radiation from inhomogeneous step profile dielectric cylinder systems are made with scattering and radiation from uniform dielectric cylinder systems (assuming that both systems have an equal bulk or average dielectric permittivity value).

ISSN:0920-5071    

DOI:10.1163/156939397X00161

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

A beam steering offset parabolic antenna with array feed is proposed for low altitude radar systems in order to minimize the undesired effect of irregular terrain obstacles between the radar and the target. This study provides information for the low altitude target located behind an obstacle. Focal region fields of the offset parabolic reflector are calculated in order to determine the array element location. Main beam of the reflector antenna with array feed is steered in order to compensate the low level field strength due to irregular terrain effects by adjusting excitation conditions of the array elements. The excitation conditions of the array elements are determined using Conjugate Gradient Method.

ISSN:0920-5071    

DOI:10.1163/156939397X00170

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Electromagnetic wave propagation in an anisotropic horizontally layered half space is considered. The anisotropy principal axes are assumed to be titled by arbitrary angles relative to the layer interfaces and a general excitation from the upper half space is allowed. It is shown that the modes of propagation are generally hybrid with distinct propagation constants for upward and downward traveling waves. The surface impedance matrix is derived and is found to have a diagnostic power for the degree of the anisotropy and its dip or tilt angle. The wave tilt on the half space interface is found to have a simple relationship to the surface impedance elements.

ISSN:0920-5071    

DOI:10.1163/156939397X00189

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

The performance of various material-based absorbers as well as absorbing boundary conditions is examined when applied to circular cylindrical boundaries. The canonical problem of scattering from a pec cylinder together with an error criterion are used to illustrate the relative absorption of the mathematical as well as the material terminations. Even though the use of an anisotropic material does not result in a perfectly matched interface, it is shown that a metal-backed layer may still outperform a second order absorbing boundary condition.

ISSN:0920-5071    

DOI:10.1163/156939397X00198

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor

摘要:

Microwave imaging of a lossless two-dimensional dielectric object buried in layered media using time domain scattering data is considered in this paper. The method is based on volume equivalence principle and moment method. Born type approximation is adopted. It is an iterative method. In each iteration, both the direct and inverse problems are solved once. The direct problem is solved by finite-difference time domain method. To overcome the ill-posedness of the inverse problem, the pseudoinverse technique is adopted. The Green function in layered media excited by a unit line current source is derived by plane wave expansion method. Several examples are given to show the ability of this method to invert arbitrarily shaped permittivity profiles. Good imaging solutions are obtained.

ISSN:0920-5071    

DOI:10.1163/156939397X00206

出版商:Taylor & Francis Group    

年代:1997

数据来源: Taylor