Showing papers in "IEEE Antennas and Propagation Magazine in 1995"
TL;DR: The matrix pencil method is described, which is more robust to noise in the sampled data and has a lower variance of the estimates of the parameters of interest than a polynomial-type method, and is also computationally more efficient.
Abstract: The approximation of a function by a sum of complex exponentials is a problem that is at least two centuries old. Fundamentally, all techniques discussed in this article proceed from using the same sequence of data samples and vary only, but importantly, in how those samples are used in achieving the parameter estimation. All of these techniques, in other words, seek the same quantitative parameters to represent the sampled data, but use different routes to get there. The techniques for estimating the parameters are either linear or nonlinear. The linear techniques are emphasized in this presentation. In particular, the matrix pencil method is described, which is more robust to noise in the sampled data. The matrix pencil approach has a lower variance of the estimates of the parameters of interest than a polynomial-type method (Prony's method belongs to this category), and is also computationally more efficient. A bandpass version of the matrix pencil can be implemented in hardware, utilizing an AT&T DSP32C chip operating in real time. A copy of the computer program implementing the matrix pencil technique is given in the appendix. >
1,153Â citations
TL;DR: In this paper, a tutorial on using genetic algorithms to optimize antenna and scattering patterns is presented, and three examples demonstrate how to optimize antennas and backscattering radar-cross-section patterns.
Abstract: This article is a tutorial on using genetic algorithms to optimize antenna and scattering patterns. Genetic algorithms are "global" numerical-optimization methods, patterned after the natural processes of genetic recombination and evolution. The algorithms encode each parameter into binary sequences, called a gene, and a set of genes is a chromosome. These chromosomes undergo natural selection, mating, and mutation, to arrive at the final optimal solution. After providing a detailed explanation of how a genetic algorithm works, and a listing of a MATLAB code, the article presents three examples. These examples demonstrate how to optimize antenna patterns and backscattering radar-cross-section patterns. Finally, additional details about algorithm design are given. >
831Â citations
TL;DR: This survey presents some of the significant works that made the FDTD method so popular, and tracks its development up to the present-day state-of-the-art in several areas.
Abstract: The finite-difference time-domain (FDTD) method is arguably the most popular numerical method for the solution of problems in electromagnetics. Although the FDTD method has existed for nearly 30 years, its popularity continues to grow as computing costs continue to decline. Furthermore, extensions and enhancements to the method are continually being published, which further broaden its appeal. Because of the tremendous amount of FDTD-related research activity, tracking the FDTD literature can be a daunting task. We present a selective survey of FDTD publications. This survey presents some of the significant works that made the FDTD method so popular, and tracks its development up to the present-day state-of-the-art in several areas. An "on-line" BibT/sub E/X database, which contains bibliographic information about many FDTD publications, is also presented. >
237Â citations
TL;DR: It is shown that tangential elements provide consistent approximations of the static solutions to wave problems, and that spurious modes are not produced by this type of finite element.
Abstract: This paper describes the problem of spurious modes that appear with finite-element solutions of the vector wave equation. It explains that this problem is caused by inconsistent approximations of the static solutions to the wave equation. Tangential-vector finite elements are described that enforce the tangential continuity of the vector field, but leave the normal component discontinuous. It is shown that tangential elements provide consistent approximations of the static solutions to wave problems, and that spurious modes are not produced by this type of finite element. Applications of the theory presented include problems from microwave and antenna design, and from electromagnetic compatibility.
135Â citations
TL;DR: In this article, the authors concentrate on the antenna-measurement research activities, and provide information on the design and development of a unique planar-near-field range, which has received a considerable amount of interest in the bipolar near-field method.
Abstract: The Electrical Engineering Department at UCLA has enjoyed the use of a new six-story building, Engineering IV, since 1989. Many exciting electromagnetic-research activities are being conducted within this building. The authors concentrate on the antenna-measurement research activities, and provide information on the design and development of a unique planar-near-field range. They have received a considerable amount of interest in the bipolar near-field method since the publication of a two-part paper (Williams et al. 1994, and Yaccarino et al. 1994). They decided to prepare the present paper in order to provide a more-tutorial description, and to present detailed measured data, images, and implementation particularities. The reader will find numerous sidebars distributed throughout the article that highlight some selected topics in planar-near-field measurements, which may be of particular interest to those readers who have not been directly involved in using or developing near-field-measurement ranges.
125Â citations
TL;DR: In this paper, the authors review some of the applications of Luneberg lenses and add some more recent data, generated using a numerical model, and compare their performance with those of other types of lenses.
Abstract: Some proposed satellite-based mobile communication systems require multibeam systems at millimeter-wave frequencies. This is a primary factor in the renewed interest in Luneberg lenses. Luneberg (1944) lenses prove useful in a variety of antenna and scattering applications. In antenna applications, their chief advantages are an ability to form multiple beams that may point in arbitrary directions, and their broadband behavior. Lens weight, and complexities involved in manufacturing such lenses, remain their primary drawbacks. Unfortunately, no significant advances in the fabrication techniques have come to pass in forty years. However, operation at millimeter-wave frequencies makes the lens weight inconsequential. The vast majority of the research on spherical lenses took place before computers were commonplace in antenna design. The author reviews some of the applications of Luneberg lenses, and adds some more recent data, generated using a numerical model. >
86Â citations
TL;DR: In this paper, the authors present the RANURS code (radar cross section-NURBS surfaces) for the analysis of the monostatic radar cross section (RCS) of electrically large complex targets.
Abstract: The paper presents the RANURS code (radar cross section-NURBS surfaces) for the analysis of the monostatic radar cross section (RCS) of electrically large complex targets. The geometric representation of the targets is given in terms of parametric surfaces, which allow an excellent fit between the model and the real surface. The parametric surfaces used are NURBS (non-uniform rational B-spline) surfaces. This technique of modeling is used in many industries to represent complex bodies. Most of the CAGD (computer aided geometric design) tools use the NURBS format for modeling, because it can represent complicated objects using limited information. Therefore, an important feature of the code is its compatibility with most of the available CAGD codes, in order to ensure that the entire design process, involving different engineering aspects (structural, mechanical, aerodynamical, electrical, etc.) can be developed with compatible models. The scattered fields are calculated by using the physical optics and the equivalent currents methods (PO+ECM). The following contributions to the RCS are taken into account: reflected field, diffracted field, double-reflected field, and diffracted-reflected field. In addition, a method for determining the hidden parts of the targets is used. The PO+ECM approach is directly applied on the parametric surfaces, and the final expressions of the fields are given as functions of the coefficients of the numerical description of the NURBS patches.
83Â citations
TL;DR: In this article, the effect of air gaps between the dielectric resonator and the adjacent conducting surfaces on a cylindrical-DR antenna is simulated by introducing air gaps.
Abstract: Results of numerical and experimental studies, pertaining to the effect of imperfections such as surface roughness, which could lead to poor mechanical contact between a dielectric resonator and the conducting surfaces on which it resides, are presented. This work simulates the poor-contact effect by introducing air gaps between the dielectric resonator (DR) and the adjacent conducting surfaces. Results are presented which illustrate the effect of air gaps upon the input impedance and resonant frequency of cylindrical-DR antennas, operating in the TM/sub 01/ and HEM/sub 11/ modes. Also presented are preliminary results pertaining to the validity of the thin-wire-theory approximation that is used in numerical electromagnetic design codes, to model the coaxial-feed probes, and results pertaining to the effect of an infinite-ground-plane assumption. >
69Â citations
TL;DR: In this article, the Riemann approximation to the time-dependent, three-dimensional problem in each spatial direction is used to eliminate the spurious-wave reflections from the numerical boundaries of the computational domain.
Abstract: Several numerical algorithms, developed in the computational-fluid-dynamics community for solving the Euler equations, are found to be equally effective for solving the Maxwell equations in the time domain. The basic approach of these numerical procedures is to achieve the Riemann approximation to the time-dependent, three-dimensional problem in each spatial direction. The three-dimensional equations are then solved by a sequence of one-dimensional problems. This approach is referred to as a characteristic-based method. The basic algorithm can be implemented for both finite-difference and finite-volume procedures, and has the potential to eliminate the spurious-wave reflections from the numerical boundaries of the computational domain. The formulation and relative merit of the finite-difference and the finite-volume approximations are presented, together with numerical results from these procedures. >
69Â citations
TL;DR: In this paper, the polar components of the radiation field have zerothor first-order p variations around the symmetry axis of the body of revolution (BO&), and conical-horn antennas can be excited by axially located electric or magnetic monopoles or dipoles.
Abstract: Several antennas are bodies of revolution @ORs), e g. conical-horn antennas and biconical antennas This note proposes to classify such antennas as types BO& and BOR,, depending on whether the polar components of the radiation field have zerothor first-order p variations around the symmetry axis of the BOR The BOR,, antennas can be excited by axially located and axially oriented electric or magnetic monopoles or dipoles The BOR., antennas can be excited by axially located and transversely orienled short electric or magnetic dipoles The note describes the general1 characteristics of B O b and BOR, antennas, and gives results for how well long half-wave dipoles can excite BOR, antennas.
60Â citations
TL;DR: In this paper, the authors proposed to use the proper Euler angles to convert the desired antenna-pattern look direction to a coordinate system better suited to the calculations. But the two systems may not even be "square" with each other.
Abstract: Antenna patterns are most naturally expressed in spherical coordinates, since the pattern angles represent directions in space. All patterns can be represented by circles on the coordinate sphere. Most patterns are either polar great-circle patterns or equatorial patterns, referring to the coordinate sphere, where all look directions lie in a plane. In some cases, however, the surface containing all of the look directions is a cone, with the origin at the antenna, and the axis along one of the Cartesian-coordinate axes. In general, all patterns are conical, known in the trade as "conics", and the axes of the cones can be in any direction. Conical patterns are useful in cases where the beam is electronically scanned, and the sidelobes in the plane perpendicular to the plane of the scan therefore fall on a cone, instead of in a plane. Additional examples are patterns of constant range or constant Doppler shift, for airborne-radar antennas, which are all conical patterns. Calculating antenna patterns, in such cases, presents a problem, since the antenna-pattern-coordinate system will generally not be the same as the antenna- or the antenna-radome-coordinate system. The two systems may not even be "square" with each other. But by using the proper Euler angles, the desired antenna-pattern look direction can be easily converted to a coordinate system better suited to the calculations. >
TL;DR: The CADDSCAT (computer-aided design drafting scattering) as discussed by the authors is a high-frequency radar cross section (RCS) analysis code based on a curved surface.
Abstract: Two basic types of physical-optics (PO)-based radar cross section (RCS) analysis codes have come to maturity in today's HF electromagnetic analysis environment. These are facet based and curved surface based codes. Facet codes have very fast analysis rates, while curved-surface codes are usually considered more accurate. At McDonnell Douglas Aerospace (MDA), the need for very reliable RCS results to guide the aircraft design process has led us to develop a curved surface based high-frequency code. This code is called CADDSCAT (computer-aided design drafting scattering). Various aspects of CADDSCAT's curved surface and facet based analysis capabilities are described and compared. Topics covered include the genesis of curved surface based PO techniques, a discussion of first-bounce PO computations, and multiple-bounce PO interactions. CADDSCAT's first-bounce and multiple-bounce PO algorithms include options for treating radar absorbing materials (RAM). The CPU needs for the ray-tracer algorithms, for curved and faceted models, are compared. Gap diffraction, resistive-card modeling, and sea-surface modeling are briefly discussed.
TL;DR: In this article, a two-dimensional super-directive antenna with one active element and a reflector made of resonant scatterers was constructed, and it was shown that changes of the angular width of a slot in an unclosed cylinder (or in several unclosed cylinders), within /spl plusmn/1%, do not lead to the destruction of the superdirective resonance.
Abstract: A brief introduction to the problem of superdirective radiation in antenna theory, and a solution to the problem of wave scattering from a structure, formed by resonant scatterers, is presented. The paper describes construction of a two-dimensional superdirective antenna with one active element, and a reflector made of resonant scatterers-unclosed cylinders proposed by Veremey and Shestopalov (see Radio Science, vol.26, no.2, p. 631-636, 1991). Physical phenomena, which cause the effect of superdirective radiation, are studied in detail. It is shown that the interaction between the resonant elements leads to the possibility of exciting a mode characterized by a high level of reactive power, in the vicinity of a passive structure. Particular attention is paid to the sensitivity of the superdirective antenna, and to tolerance constraints. It is shown that changes of the angular width of a slot in an unclosed cylinder (or in several unclosed cylinders), within /spl plusmn/1%, do not lead to the destruction of the superdirective resonance. >
TL;DR: This paper discusses the efficient solution of dense systems of linear equations, arising from integral-equation formulations, using Krylov iterative solvers for magnetostatic volume-integral formulation.
Abstract: This paper discusses the efficient solution of dense systems of linear equations, arising from integral-equation formulations. Several preconditioners, in connection with Krylov iterative solvers, are examined, and compared with LU factorization. Results are shown, demonstrating practical aspects and issues we have encountered in implementing iterative solvers, on both parallel and sequential computers, for a magnetostatic volume-integral formulation.
TL;DR: A generalized approach to analytical surface-ray tracing in three dimensions, and a review of its application to convex conducting bodies, using the Eisenhart coordinate system, is presented, and the ray-parameters so obtained, for quadric cylinders (QUACYL) and surfaces of revolution (QUASORs), are in a one-parameter form for UTD mutual-coupling applications.
Abstract: A generalized approach to analytical surface-ray tracing in three dimensions, and a review of its application to convex conducting bodies, is presented, using the Eisenhart coordinate system. The ray-parameters so obtained, for quadric cylinders (QUACYLs) and surfaces of revolution (QUASORs), are in a one-parameter form for UTD mutual-coupling applications. The ray analysis is also extended to the hybrid QUACYLs (e.g. aircraft wings) and hybrid QUASORs (e.g., satellite-launch vehicles), by introducing Hertz's principle of particle dynamics to EM theory. This mathematical formulation is applicable even to other important non-Eisenhart surfaces, such as the ogive. A summary of the mathematical formulations is included. >
TL;DR: Methods of parallelizing the core FDTD algorithm, PML ABC, Mur's ABCs, and the near-zone-to-far-zone transformation are discussed, and a technique which makes the parallel FDTD more efficient can be applied to Berenger's PML in a straightforward manner.
Abstract: In this paper, techniques for efficiently parallelizing the FDTD method for radiation problems are presented. Methods of parallelizing the core FDTD algorithm, PML ABC, Mur's ABCs, and the near-zone-to-far-zone transformation are discussed. A technique which makes the parallel FDTD more efficient can be applied to Berenger's PML in a straightforward manner, and apparently makes the code for PML ABC faster. Performance of the code is shown, and the computer-time usage for various parts of the code is given. On a 32 processor CM-5, the core FDTD algorithm is 100 times faster than an existing serial code, run on a SUN SPARC-2 workstation, and the calculation of the radiation patterns for two orthogonal planes is approximately 27 times faster. The techniques can easily be extended to other cases, not included in this paper, such as FDTD codes for magnetic materials, and non-uniform-mesh FDTD codes.
TL;DR: In this paper, the authors recall the construction used in optics, known as Huygens' principle, which states that every point on a wavefront can be regarded as a source of radiation.
Abstract: In principle, any desired amount of gain can be developed from an antenna of arbitrary size. The phenomena of high gain from very small antennas is called "supergain". To see why this statement might be so, the author recalls the construction used in optics, known as Huygens' principle. This states that every point on a wavefront can be regarded as a source of radiation. At the end of a short period of time, the envelope of all of these individual wavelets forms the new wavefront. For example, this construct explains why a shadow is not perfectly sharp, and why interference fringes form. End fire antennas, dipole antennas, Yagi antennas and quad antennas are examined. >
TL;DR: In this article, the concept of group velocity, wave front velocity, and wave precursors in a rectangular waveguide was introduced and simple experiments were performed to validate the theory.
Abstract: Transient propagation in a rectangular waveguide is examined, using elementary dispersion theory. Simple experiments are presented, which validate the theory and illustrate the concepts of group velocity, wave-front velocity, and wave precursors in a rectangular waveguide. The precursor phenomenon is isolated by examining the step response of the waveguide, using a time-domain reflectometer, showing that the wavefront velocity never exceeds the speed of light. >
TL;DR: In this paper, the authors show that such a consistency requirement results in a mathematical constraint: an algebraic relation between the constitutive parameters of a linear bi-anisotropic media.
Abstract: While physical restrictions on the constitutive parameters of linear bi-anisotropic media are well known, attention has been meager on the issue of mathematical consistency, when specializing the Maxwell equations for material media. The authors show that such a consistency requirement results in a mathematical constraint: an algebraic relation between the constitutive parameters. Repercussions for specific types of linear media are discussed, most importantly, the consequence that bi-isotropic media must be reciprocal. >
TL;DR: In this article, the authors presented images from data obtained with a finite-volume time-domain (FVTD) code and provided relations between the range and resolution of the bistatic scattering data in the Fourier domain, and the pixel resolution and image extent in the physical domain for the down-range and cross-range directions.
Abstract: Inverse-synthetic-aperture-radar (ISAR) images of radar targets are useful for target identification, visualization, and the analysis of scattering centers. The major advantage of bistatic over monostatic-ISAR imaging is the reduction, in the number of computed incident angles, from hundreds to one. This advantage has already been demonstrated for a physical theory of diffraction (PTD) code, XPATCH. The bistatic-imaging technique can be extended to scattering data obtained from any time-accurate or iterative method, including low-frequency algorithms. This paper presents images from data obtained with a finite-volume time-domain (FVTD) code. It also provides relations between (1) the range and resolution of the bistatic scattering data in the Fourier domain, and (2) the pixel resolution and image extent in the physical domain for the down-range and cross-range directions. A tapering function is applied in the Fourier domain, to dampen ringing effects. Results are shown for a trapezoidal plate, a cone-sphere, and a square-aperture cavity.
TL;DR: In this paper, a 2/spl times/2 element planar microstrip-patch sub-array is described for the 35 GHz band, which can be used as a basis configuration for design of large, high-gain arrays.
Abstract: A classical configuration of a planar array of microstrip rectangular patches, fed by a corporate-feed arrangement, is widely used for many applications. There are several reports devoted to the design of such antennas. However, they are based on semi-empirical approaches, especially at mm-wave frequencies. A good choice of an array-feeding-network layout is a cornerstone problem for the antenna's design. The purpose of this report is to give a description of a 2/spl times/2 element planar microstrip-patch sub-array, which can be used as a basis configuration for design of large, high-gain arrays, for the 35 GHz band.
TL;DR: In this paper, a general-purpose simulation program based on the three-dimensional symmetrical-condensed TLM model is presented, which is applied to the characterization of aperture-coupled microstrip structures.
Abstract: The transmission-line-matrix method is a numerical technique for solving Maxwell's equations in the presence of complex environments. A general-purpose simulation program, based on the three-dimensional symmetrical-condensed TLM model, is presented. Previous applications of the simulation program include the analysis of half-space and remote-sensing problems, and calculation of the radar cross section of finite-sized conducting materials and objects. The simulation program is applied to the characterization of aperture-coupled microstrip structures. Numerical results, pertaining to the analysis of aperture-coupled microstrip lines, offset-aperture-coupled microstrip lines, and aperture-coupled microstrip-patch antennas, indicate the accuracy and utility of the program for analyzing aperture-coupled microstrip configurations. A discussion of the accuracy and efficiency of the approach is included, with limitations and possible improvements. >
TL;DR: The authors introduce the different methods for performing the domain decomposition for distributed memory, multiple-instruction multiple-data (MIMD) multiprocessors and assume that an iterative-matrix method, such as the conjugate gradient method, is used to solve the matrix equation.
Abstract: The finite-element solution of electromagnetic phenomena, involving electrically large and complex structures, is a major challenge, since both accuracy and efficiency are hard to obtain. The authors introduce the different methods for performing the domain decomposition for distributed memory, multiple-instruction multiple-data (MIMD) multiprocessors. In discussing the advantages and disadvantages of the different methods, we assume that an iterative-matrix method, such as the conjugate gradient method, is used to solve the matrix equation. >
TL;DR: In this paper, the authors investigated and derived a simple equivalent circuit model to represent an electromagnetically coupled microstrip-patch antenna, based on broadside-coupled lines and improved-transmission-line methods, to provide for the practical design of such antennas without involving complicated, time-consuming, difficult numerical methods.
Abstract: This work is an effort to investigate and derive a simple equivalent-circuit model to represent an electromagnetically coupled microstrip-patch antenna. A simplified theory is developed, based on the broadside-coupled lines and improved-transmission-line methods, to provide for the practical design of such antennas without involving complicated, time-consuming, difficult numerical methods. A number of sample patches are designed, made, and tested to verify the theory. These patches are also incorporated into an array, to evaluate their performance in an array environment. >
TL;DR: A FORTRAN subroutine is presented, which accurately determines the effective width of a waveguide and its length, by measuring the resonance frequencies of the cavity made of the same waveguide.
Abstract: A FORTRAN subroutine is presented, which accurately determines the effective width of a waveguide and its length, by measuring the resonance frequencies of the cavity made of the same waveguide. This measurement method only necessitates a scalar network analyzer and standard waveguide components. >
TL;DR: In this paper, a reconstruction algorithm and equipment have been developed for microwave imaging, with emphasis on noninvasive control of deep hyperthermia treatments, for qualitative spectral and quantitative spatial iterations, and the data can be accessed from the e-mail address ftp voltor.upc.es.
Abstract: Reconstruction algorithms and equipment have been developed for microwave imaging, with emphasis on noninvasive control of deep hyperthermia treatments. Tomographic reconstruction algorithms have also been developed for qualitative spectral and quantitative spatial iterations. The data can be accessed from the e-mail address ftp voltor.upc.es.
TL;DR: In this paper, the authors discuss some of the lesser-known events predating the first attempted rise of the new technology of wireless telegraphy, for military communications during the Anglo-Boer War of 1899-1902.
Abstract: This article discusses some of the lesser-known events predating the first attempted rise of the new technology of wireless telegraphy, for military communications during the Anglo-Boer War of 1899-1902. Copious use has been made of original and little-known documentary material to prepare this paper. Much of this material has never been published before. As such, the article provides an interesting insight into the way that the pioneers in the field tried to come to grips with a technology which would ultimately have a major impact on society.
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TL;DR: A new version, MININEC Professional for Windows, is described, along with the application of this new version.
Abstract: A brief history of the development of MININEC is presented. Differences between MININEC and NEC are discussed. A new version, MININEC Professional for Windows, is described, along with the application of this new version. The original purpose of the code was to provide a tool for the rapid analysis of simple, relatively small (in terms of wavelengths) antenna structures. >
TL;DR: ASYRIO as discussed by the authors is a development program, carried out at CASA's facilities under an ESA (ESTEC) contract, which aims at the development of reconfigurable microwave devices and their application to an antenna system for communications satellites with flexible-coverage illumination and reconfigurability.
Abstract: ASYRIO is a development program, carried out at CASA's facilities under an ESA (ESTEC) contract. The objective is the technological development of reconfigurable microwave devices, and their application to an antenna system for communications satellites with flexible-coverage illumination and reconfigurable missions. The associated hardware consists of an antenna-feed demonstration model, and a set of space-qualified reconfigurable components. These are to be capable of operation in space conditions, and reconfigurable through software control from an earth master station. A scenario has been tried for the second generation of Spanish-telecommunication satellites. This scenario is the fundamental input for antenna-system requirements. It presents supranational-coverage characteristics. It is for use where a flexible mission is needed or desired; detailed analysis of each particular case shows the more-appropriate reconfiguration implementation. A multibeam-reflector antenna has been accepted as the baseline for a high-gain-antenna definition, with a fixed-parabolic reflector, and a reconfigurable multibeam-feed subsystem. Reconfigurability is accomplished by the variable components assembled in the feed beam-forming network. The feed-demonstration model that supports the Spanish mission has been designed, manufactured, and tested, both electrically and thermomechanically, to verify its compliance with space geostationary environmental conditions during and after launch. >
TL;DR: Describes a computer code, for computing the reflectivity of corrugated periodic surfaces at all incidence angles, including skew incidences (i.e., the 2.5D problem).
Abstract: Describes a computer code, for computing the reflectivity of corrugated periodic surfaces at all incidence angles, including skew incidences (i.e., the 2.5D problem). This is a self-contained code, and is available from the authors. Since the finite element method is employed for modeling the corrugations, the periodic cell can be of any shape and material composition, and this is one of the most attractive features of the finite-element and derivative methods. Metallic and non-metallic cells can be considered and, because a boundary integral is used for truncating the mesh, this hybrid approach is rigorous. >