摘要:

Recent studies have shown that large circular arrays of perfectly conducting vertical dipoles with only two dipoles driven possess very narrow resonances. The remaining dipoles are parasitic and unloaded. The field pattern of the resonant circular array is adequately determined from a continuous-current model of the discrete array. This field pattern is omnidirectional in the azimuth. In this paper, the continuous-current model is generalized to the case of resonant noncircular closed-loop arrays, and the resulting field patterns are determined. A class of closed curves is considered, the shape of which is nearly circular. It is shown that the radiation field can be drastically different from that of the circular array and that, for proper choices of the parameters, the field pattern in the azimuth plane consists of a single, very narrow radiated beam.

ISSN:0920-5071    

DOI:10.1163/156939396X00432

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The electromagnetic fields due to an electrically small current loop located above a chiral half space are derived in integral forms that can be evaluated numerically. It is shown that for a loop whose axis is perpendicular to the air/chiral interface, the fields have both TE and TM components. The latter is a direct result of chirality. Therefore, the chirality parameter can be inferred from the ratio of TM to TE field components. Approximate, but sufficiently accurate closed forms are derived for the fields in the near zone or under the quasistatic condition kor < 1. A simple image theory is developed to approximate the TE and TM fields in the air region when kor > 1. It is shown that the image theory is sufficiently accurate except when used to evaluate the field very near to the air/chiral interface.

ISSN:0920-5071    

DOI:10.1163/156939396X00441

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

Several different memory-based neural networks are used to discriminate radar targets based on their early-time, aspect-dependent response. The beginning of the response is difficult to locate in practice, so we use only the magnitude of the time response's DFT Spectrum as input to the neural network, thus eliminating time-shift uncertainty. Especially promising is the Recurrent Correlation Accumulation Adaptive Memory-Generalized Inverse (RCAAM-GI) cascade neural network. From the simulation results, the network demonstrates a decision strategy which is flexible, parallel adaptive, computation space efficient, and highly noise tolerant. Performances of the networks presented in this paper are compared with those of existing networks.

ISSN:0920-5071    

DOI:10.1163/156939396X00450

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

A design method previously developed to give distributions with a minimal edge brightening for sum patterns with arbitrary sidelobe topography is shown to be applicable to difference patterns as well. The method is based on obtaining some null-filling in the desired pattern that provides a multiplicity of solutions, some of which may be smoother than that corresponding to the pattern with deep nulls. The improvement in the aperture distributions, for linear and planar array synthesis, is found to be very good with the resulting loss in directivity being small.

ISSN:0920-5071    

DOI:10.1163/156939396X00469

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939396X00478

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The reconstruction of spatial source distributions on a nonuniform LCRG line is considered in the time-domain. An optimization approach is used to reconstruct two source distribution functions (induced by electric and magnetic fields, respectively) using the received transient voltages at the two endpoints of the line. By introducing auxiliary functions, the gradient of the objective functional is found as an explicit expression. The two source distribution functions are then reconstructed simultaneously by an iterative algorithm (the conjugate gradient method). Numerical results show that the present algorithm for the reconstruction is robust, and stable under noise of the measured signals and any perturbation of the known parameters. Conditions for a reliable simultaneous reconstruction using only one-sided measurements are also discussed and tested numerically.

ISSN:0920-5071    

DOI:10.1163/156939396X00487

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939396X00496

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

In this paper we redevelop the scalar and dyadic Green functions of electromagnetic theory using differential forms. The Green dyadic becomes a double form, which is a differential form in one space with coefficients that are forms in another space, or a differential form-valued form. The results presented here correspond closely with the usual dyadic treatment, but are clearer and more intuitive. Many of the usual expressions using green functions in vector notation require a surface normal; with the Green forms the surface normal is unnecessary. We illustrate the formalism by computing scattering from a randomly rough conducting surface and deriving the Green form for a dielectric half-space. We also define the interior derivative, which is equivalent to the coderivative but for a constant metric has a computational rule dual to that of the exterior derivative and simplifies calculation in coordinates. This work makes available some of the tools that have not yet been presented in the language of differential forms but are essential in applied electromagnetics.

ISSN:0920-5071    

DOI:10.1163/156939396X00504

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

摘要:

The impedance and radiation properties of an electromagnetically fed concentric microstrip ring antenna using log-periodic principle is investigated experimentally and compared with those of two single ring resonators. The experimental result is verified numerically by Finite Difference Time Domain (FDTD) method. The variation of voltage standing wave ratio with frequency is also measured and computed numerically for both the single rings and concentric structure. The comparison between numerical and experimental results shows good agreement over a wide frequency range. The results indicate a considerable improvement of 1:2 VSWR bandwidth for the concentric structure.

ISSN:0920-5071    

DOI:10.1163/156939396X00513

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939396X00522

出版商:Taylor & Francis Group    

年代:1996

数据来源: Taylor