摘要:

We have studied the plane electromagnetic wave scattering at higher harmonics by system of two or four parallel thin metallic dipoles with a nonlinear local load (in the form of. a semicinductor diode) placed in a free space as dependent on the distance between scatterers, the location and the direction of nonlinear load. Also we considered the influence of an air-dielectric boundary on the back scattered field of an oscillator and loop with a semiconductor diode located near the interface.

ISSN:0272-6343    

DOI:10.1080/02726349808908602

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The accurate estimation of the electromagnetic field inside the human head is of extreme importance, in mobile communications. A method based on the numerical method of moments, that takes into account both the induced eddy currents and the charge accumulation is presented, for the determination of the electric field intensity, the eddy current density and the S.A.R. inside the head. The excitation is a non uniform electromagnetic field, produced by a monopole antenna that is typically used in mobile communications. Examples for an inhomogeneous model of the head in cylindrical coordinates are given.

ISSN:0272-6343    

DOI:10.1080/02726349808908603

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In this paper we present a generalized theory of higher order vector finite elements. This theory aims at generating tctrahedral Whitney elements with tangential continuity, having better orders of approximation compared to the well-known first order edge elements. The proposed methodology deals with some fundamental theoretical issues about Whitney elements, such as the proper definition of degrees of freedom and the correct modeling of the nullspace of the curl operator, corresponding to the class of irrotational fields. The whole set of properties is enforced to the shape functions, in order to produce their explicit expressions. The new second and third order vector finite elements are implemented in a formulation for 3-D electromagnetic scattering. A second order absorbing boundary condition for rectangular boundaries is used to truncate the infinite space. The numerical results show the improved accuracy of the approximation, obtained by the use of higher order Whitney elements, thus rendering them a promising tool for electromagnetic analysis.

ISSN:0272-6343    

DOI:10.1080/02726349808908604

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The problems of optimization of the planar resonant or leaky-wave antennas with waveguide excitation are considered. The directivity factor in some frequency range or deviation of the amplitude pattern from the desired one is optimized. The optimization algorithm consists of transformation of the outer problem to inner one, and of using the following combined methods: local variations, cross-sections, opposite directions, and basic problems of excitations. Numerical results for the resonant antenna and the detailed algorithm description for the leaky-wave antenna are presented.

ISSN:0272-6343    

DOI:10.1080/02726349808908605

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The arrangement of a Mast-mounted folded dipole antenna array with corner reflectors is considered. The method of moments (MoM) in a wire grid model is used and a suitable optimization procedure is applied Due to the constraints for high power gain and low SLL the array is designed as a simple broadside Chebyshev one. The presence of 120° corner reflectors change the pattern and makes the array to be a Hybrid-Chebyshev one with approximately the same SLL. The distance of the array from the corner of the reflector is critical for the HPBW. Two different types of antennas with 60° and 120° HPBW in the horizontal plane for possible mobile applications are studied.The whole design work is given in a general form, useful for VHF and UHF communication applications. To ensure the accuracy, two different wire grids for each model are used. In the examples several interesting cases will be analytically presented.

ISSN:0272-6343    

DOI:10.1080/02726349808908606

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

To reduce the number of driven elements in a broadside colinear antenna array, in narrowband applications COCO (coaxial colinear) antennas have been used since relatively recently, either as isolated elements, or as parts of antenna arrays. COCO antennas have a single actual port, but the driving voltage is transmitted to several other ports via transposed segments of a coaxial cable of which the antenna is made, resulting in approximately cophasal currents along the COCO antenna segments. This paper is aimed at demonstrating that COCO antennas are a special case of a new wide class of one-port, multiply-excited antennas (“OPOMEX” antennas), which can be in a variety of forms, including printed versions. The design of OPOMEX antennas is significantly more flexible than that of COCO antennas, since they have more parameters that in practical realizations can be varied easily. The paper describes two approximate methods for the analysis of OPOMEX antennas, and presents numerical and experimental results for a number of such printed-strip antennas. Numerical results are found to be in reasonable agreement with experiment.

ISSN:0272-6343    

DOI:10.1080/02726349808908607

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The problem of synthesis of the given shape contoured directivity pattern of spacecraft hybrid antenna with purpose of uniform “illumination” of the some territorial zone is considered. The variational formulation of the synthesis problem according to the given magnitude pattern is used. The mean-square deviation of given and synthesized magnitudes is chosen as optimization criterion. It permits to improve the approximation quality of the magnitudes, to influence by a certain mean on polarized properties of synthesized directivity patterns, and also to satisfy set additional requirements. Examples of synthesis of the contoured directivity patterns, which covers uniform the given territory are presented. In these examples, the hybrid antenna consisting of the rectangular cutting from a parabolic reflector and flat feed array is used.

ISSN:0272-6343    

DOI:10.1080/02726349808908608

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This article describes a new relationship between the two-dimensional high-frequency and low-frequency waves scattered by an obstacle with a sharp wedge. It is shown that these two extremal waves have a unique correspondence in the underlying description of electromagnetic fields. The low-frequency field, which is given as a quasi-static field, is represented in terms of a function of complex variable z = x + iy. The high-frequency field can also be represented in terms of this complex function. The time-harmonic electromagnetic scattered or diffracted fields varying with exp(jωt) are thus bicomplex, which contains two imaginary units i and j. Basic concepts for this bicomplex calculations were discussed in the early paper. To illustrate the new solution in comparison with the exact one, the result is extended here to a half-plane diffraction known as a canonical problem. The same idea is tested to obtain a uniform solution that has no geometric-optical singularity in the far zone.

ISSN:0272-6343    

DOI:10.1080/02726349808908609

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor