摘要:

Arbitrarily shaped, coax-fed microstrip patch antennas with substrates that may be electrically thick are studied using a mixed-potential integral equation approach. Vector basis functions defined over triangular elements are used to approximate the current distribution on the conducting patch. Rigorous and simplified models of the probe-to-patch junction, compatible with the triangular element model of the microstrip patch, are implemented and their relative merits are discussed. Two models of the coaxial probe, differing in accuracy and complexity, are also implemented and their ranges of validity are examined. Input impedance data for several microstrip patch antennas of different shapes, computed using different coax feed models, are presented and compared with measured results.

ISSN:0920-5071    

DOI:10.1163/156939391X00860

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

A moving spot illuminated semiconductor panel is used to convert millimeter wave images to visible displays. The response of semiconductors to moving spot illumination is important in this method. In this paper the response of a semiconductor panel to a moving Gaussian (laser) spot is considered in detail. Initially, the profile of excess carrier in the bulk of the semiconductor panel for Gaussian illumination vs. width, scanning, velocity, width of the semiconductor panel, etc., are studied. Using the expression for excess carrier, the single path attenuation of a millimeter wave through moving Gaussian spot illuminated semiconductor panel vs. standard deviation of Gaussian spot and scanning velocity is studied. The effect of the intensity of illumination, scanning velocity, and width of illumination spot on the sensitivity of the system is considered. An optimum choice of the parameters of the system is also considered.

ISSN:0920-5071    

DOI:10.1163/156939391X00879

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

An inversion method for microwave imaging is presented that is independent of the shape of the interrogated object. The method is based on the application of the sampling theorem to solve the integral equation that describes the scattering problem and a multifrequency measurement scheme to provide the necessary data for the iterative inversion algorithm proposed. Numerical results obtained from simulations on known objects are presented.

ISSN:0920-5071    

DOI:10.1163/156939391X00888

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Field theories such as Maxwell's equations for electrodynamics describe a continuum and predict the existence of waves. A contact to mechanics and its classical kinematical concepts of localized objects, or particles, moving at certain group velocities along well-defined trajectories, is achieved by defining wave packets and developing the Hamilton ray equations governing their motion. The wave packets contain many oscillations which are modulated by a slowly tapering envelope defining the extent of this packet in space and time. It is shown here that the solitary waves, i.e., waves which are characterized by very sharp localized pulses consisting of a small number of oscillations, are described differently. The two entities are analogous when we compare the behavior of one in configuration space-time with the other in representation space. This analogy is remarkable and leads to new concepts that might prove useful for many applications. Thus it is shown that the solitary wave can be described in terms of analog rays in representation space, on which a group slowness function is defined. In space-time the solitary wave is characterized by a wave surface evolving according to the relevant slowness function at each point. For objects and therefore for wave packets, there exists a relativistic formalism in terms of four-vectors. Thus the Hamilton ray equations can be represented in terms of the four-velocity, involving a differentiation of the position four-vector with respect to the proper time. The analog treatment leads to a differentiation of the representation four-vector with respect to the new concept: the proper frequency. Finally, the analogy provides an explanation for the stability of solitary waves in the presence of nonlinear media, without the need for discussing specific differential equations: It is argued that self defocusing of the analog rays in representation space provides the "glue" which counteracts dispersive effects in configuration space, and thus obviates the fissioning of the solitary wave.

ISSN:0920-5071    

DOI:10.1163/156939391X00897

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

Diffraction from an abruptly terminated single mode fiber waveguide is treated analytically. A step index waveguide carrying the fundamental HE11, mode, incident on the abruptly terminated aperture, is assumed. The diffracted fields inside the fiber and free space regions are described in terms of the mixed spectrum vector eigenwaves. In treating the field of the fiber waveguide a full spectrum of guided and radiation modes is employed without making use of the weak guidance approximation. An integral equation is developed on the abruptly terminated fiber waveguide aperture in terms of the unknown aperture electric field. This equation is solved approximately by applying an iterative technique. Numerical results are presented for the reflection coefficient of the HE11, mode and the radiation far field in the free space region.

ISSN:0920-5071    

DOI:10.1163/156939391X00905

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

摘要:

An approximate solution for the problem of wave diffraction from irregular surfaces with small height and small slope irregularities can be obtained using the small perturbation method (SPM). If the irregularities have large heights but their radii of curvature are much larger than the radiation wavelength, the tangent plane method (TPM) is usually used. In this paper we propose a new method for solving the problem of diffraction from a surface with small slope irregularities of arbitrary height: the local perturbation method (LPM). It allows us to obtain the result in the form of an iteration series which is an asymptotic expansion in two small parameters. The characteristic slope is one of them, and the other one characterizes radii of curvature of the irregularities on the scale of the electromagnetic field changing near the surface. In the appropriate limits the result coincides with those obtained by the SPM or TPM. With the help of the LPM we have shown that some integral characteristics of scattering can be computed by the formulae of the SPM for irregularities with arbitrary height.

ISSN:0920-5071    

DOI:10.1163/156939391X00914

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939391X00923

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939391X00932

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor

ISSN:0920-5071    

DOI:10.1163/156939391X00941

出版商:Taylor & Francis Group    

年代:1991

数据来源: Taylor