Showing papers in "IEEE Antennas and Propagation Magazine in 1996"
TL;DR: In this article, an iterative-reconstruction algorithm based on a conjugate-gradient method was proposed to reconstruct the complex permittivity profile of lossy dielectric objects from measured far-lied data.
Abstract: The reconstruct of the complex permittivity profile of lossy dielectric objects from measured far-lied data is considered, with application to perfectly conducting (PEC) objects. From an integral representation of the electric field (EFIE), and applying a moment-method solution, an iterative-reconstruction algorithm based on a conjugate-gradient method, is derived. In order to start the iterative procedure with an initial guess, a back-propagation scheme is used. For testing the algorithm on real, measured data, the reconstruction of two PEC (cylinder and strip) objects is presented.
71 citations
TL;DR: In this paper, the authors present a theoretical proof for the existence of the ideal CPSS, and identify some geometrical constraints inherent to such a device, and present the results of numerical computations.
Abstract: This paper presents the concept of an electromagnetic surface called the circular-polarization-selective surface (CPSS). Few papers have dealt with the CPSS, and it has even been argued that the ideal CPSS belongs to the category of impossible polarizers. We present herein a theoretical proof for the existence of the ideal CPSS, review the prior art in this area, identify some geometrical constraints inherent to such a device, and present the results of numerical computations.
68 citations
60 citations
TL;DR: This paper describes a cavity-backed patch-antenna geometry, which features multiple dielectric layers and shorting posts, which is exploited to design antennas which retain many of the desirable characteristics of conventional microstrip antennas, yet overcome some of their inherent disadvantages.
Abstract: This paper describes a cavity-backed patch-antenna geometry, which features multiple dielectric layers and shorting posts. These features are exploited to design antennas which retain many of the desirable characteristics of conventional microstrip antennas, yet overcome some of their inherent disadvantages.
57 citations
TL;DR: In this paper, the impedance-boundary condition (IBC) was also derived independently by another Russian scientist, A.N. Shchulkin, in his book, Propagation of Radio Waves.
Abstract: Part of the material presented in this article has been collected in the framework of a research activity on the history of ray optics. The aim of this project is collect some reprints of the most-significant original papers of the history of ray optics, from the seventeenth century (i.e., from the work by Rene Descartes) up to now. The purpose of the article is to show that the impedance-boundary condition (IBC)-usually referred both in western countries and in the former USSR as the Leontovich condition was also derived independently by another Russian scientist, A.N. Shchulkin. He published the IBC in 1940, in his book, Propagation of Radio Waves.
54 citations
TL;DR: In this paper, a general, multi-factor, parametric approach to system modeling, called Kriging, is presented, which leads to adequate prediction, together with an estimation of the accuracy of the predicted values of an observable, although the model is based on outrageously simplistic equations.
Abstract: This article reviews a very general, multi-factor, parametric approach to system modeling, called Kriging. It is shown how this method can lead to adequate prediction, together with an estimation of the accuracy of the predicted values of an observable, although the model is based on outrageously simplistic equations (and thus "wrong", from a phenomenological point of view). Kriging appears to be a useful approach for many applications in electromagnetics, in particular in those where computational time is an important issue. This is true when the simultaneous analysis of an observable with respect to more than one factor is needed.
44 citations
TL;DR: In this paper, the history and present state of finite-element methods, as applied to electromagnetic-field problems in the microwave range, are reviewed, including element definitions and error estimation, guided wave propagation, scattering and antenna problems.
Abstract: This paper reviews the history and present state of finite-element methods, as applied to electromagnetic-field problems in the microwave range (including element definitions and error estimation, guided wave propagation, scattering and antenna problems). It provides a selective bibliography, current as of the first months of 1996, with annotations and evaluative comments on the works surveyed. It briefly notes the capabilities of the finite-element method, and estimates how fully they have been realized to date. Some conjectures on the future of finite-element methods are also hazarded.
43 citations
TL;DR: In this paper, the authors define the ambiguity functional, generalization of the radar and sonar ambiguity functions, which applies not only to wideband signals, but also to targets and radar platforms executing arbitrary nonlinear motions.
Abstract: Physical wavelets are acoustic or electromagnetic waves, resulting from the emission of a time signal by a localized acoustic or electromagnetic source moving along an arbitrary trajectory in space. Thus, they are localized solutions of the wave equation or Maxwell's equations. Under suitable conditions, such wavelets can be used as "basis" functions, to construct general acoustic or electromagnetic waves. This gives a local alternative to the construction of such waves in terms of (nonlocal) plane waves, via Fourier transforms. We give a brief, self-contained introduction to physical wavelets, and apply them to remote sensing. We define the ambiguity functional, generalization of the radar and sonar ambiguity functions, which applies not only to wideband signals, but also to targets and radar platforms executing arbitrary nonlinear motions.
42 citations
TL;DR: In this article, a review of different methods, developed to estimate average properties of helix-loaded materials, is given, including the effective properties of a chiral slab, such as the rotation angle, ellipticity, permittivity, and permeability.
Abstract: After a brief overview of the concepts of electromagnetic chirality and wave propagation in chiral media, this paper deals with the field of microwave-chiral-material modeling. First, studies regarding the scattering of single-chiral or non-chiral elements with different shapes (various designs of helices, /spl Omega/-shaped scatterers, wires, and loops) are presented. Results of the backscattered field given by different computer codes are compared. Comparisons among analytical, numerical, and experimental results are also reported. Second, the case of a collection of chiral inclusions is treated. A review of different methods, developed to estimate average properties of helix-loaded materials, is given. Modeling of the effective properties of a chiral slab, such as the rotation angle, ellipticity, permittivity, and permeability, is explored. Reflection and transmission coefficients, evaluated by various methods, are compared with each other, and with measurements. Limitations of the models, possible improvements, and new directions for research are also described. Finally, applications of such composites to the design of radar-absorbing materials are addressed.
40 citations
TL;DR: This column concludes with a brief description of VMAP 3.2, a graphics program from Professor Kajfez, of the University of Mississippi, and a user-oriented comparison of popular PC operating systems.
Abstract: Items discussed in this column include how communications have changed, and whether past ideas of courtesy apply to these new technologies. Along the same line is a discussion on the commitment an author makes when having a paper accepted for presentation at a meeting. A fundamental engineering/physics question is then considered, which can be stated succinctly as "Why does an antenna radiate?" The column concludes with a brief description of VMAP 3.2, a graphics program from Professor Kajfez, of the University of Mississippi, and a user-oriented comparison of popular PC operating systems.
38 citations
TL;DR: A review of the available literature on numerical integration over triangular and tetrahedral domains can be found in this article, with a focus on two-dimensional numerical integration methods and their applications in electromagnetics.
Abstract: Many computational methods in electromagnetics, including the method of moments (MoM) and the finite-element method (FEM), require integrating a function over a given domain. In many cases, analytical solutions for the integrals are not available, and some type of numerical integration must be used. One-dimensional numerical-integration techniques are widespread throughout popular mathematical and engineering texts. However, two-dimensional and three-dimensional numerical-integration methods are discussed only in specialized reports and journal articles, and almost never in the electrical engineering literature. This synopsis reviews the available literature on numerical integration over triangular and tetrahedral domains.
TL;DR: In this paper, the authors concentrate on the scattering by sprites of man-made VLF radio waves, and show that the columnar elements of sprites have a substantial electrical conductivity.
Abstract: Red sprites occur high above the stratosphere, just under the ionosphere. Although the first reported observation was over 100 years ago, and the first theory was 40 years ago, only over the last year or so has the subject spread into the popular science magazines, and into the secular media. Most of the studies of the sprite structure have been optical, using the light they emit for a few tens of milliseconds for imaging (low-light video and photography) and spectroscopy. Here, we concentrate on the scattering by sprites of man-made VLF radio waves. This scattering shows that the columnar elements of sprites have a substantial electrical conductivity.
TL;DR: The basic theory implemented in the WIPL program, and some results concerning TV UHF panel antennas and large horn antennas are given are given.
Abstract: WIPL is a program which allows fast and accurate analysis of antennas. The geometry of any metallic structure (even a very large structure) is defined as a combination of wires and plates. WIPL's analysis features include evaluations of the current distribution, near and far field, and impedance, admittance and s-parameters. The program uses an entire-domain Galerkin method. Efficiency of the program is based on the flexible geometrical model, and sophisticated basis functions. In this paper, the basic theory implemented in the program, and some results concerning TV UHF panel antennas and large horn antennas are given.
TL;DR: Comparisons between measurements and calculations are presented, along with a qualitative description of the finite-element and high-frequency codes employed, for predicting the radiation pattern of printed antennas mounted on aircraft platforms.
Abstract: This paper considers the hybridization of the finite-element and high-frequency methods for predicting the radiation pattern of printed antennas mounted on aircraft platforms. The finite-element method is used to model the cavity-backed antennas, whereas the interactions between the radiators and the substructures are treated via a high-frequency technique, such as the GTD, PO/PTD, or SBR. We present comparisons between measurements and calculations, along with a qualitative description of the finite-element and high-frequency codes employed.
TL;DR: In this paper, a new nomograph calculates the polarization efficiency to be used in a link budget, when the gain of the antennas have been measured with respect to a pure-polarization incident wave.
Abstract: What is the correct polarization loss, when calculating the transmission between two antennas whose gains are measured with respect to circular polarization, such as, from a ground station to a satellite? Previously published charts made assumptions, which do not quite fit this situation. We need to revisit this problem, and be made aware of the assumptions behind these charts, so that we obtain the right answer. In general, the previous charts over-estimate the loss. All these charts are correct when used in the proper situation. As a part of this discussion, the author also covers methods of measuring the gain of circularly polarized antennas. A new nomograph calculates the polarization efficiency to be used in a link budget, when the gain of the antennas have been measured with respect to a pure-polarization incident wave. A comparison is made to previous nomographs, and the assumptions made in deriving them.
TL;DR: In this paper, the authors present a review of scientific work concerning scattering by objects with edges, corners, tips, etc., and apply a mathematical transformation for the acceleration of convergence to these expansions, to numerically determine the scattering cross sections of these objects.
Abstract: The spherical-multipole analysis of scalar scattering by an acoustically soft or hard elliptic cone, and of electromagnetic scattering by a perfectly conducting elliptic cone, are presented. The series expansions of the exact solutions are of poor convergence, if both source and field points are far from the cone's tip. A mathematical transformation for the acceleration of convergence-due to Euler-is applied to these expansions, to numerically determine the scattering cross sections of these objects. This powerful method can also be used for the numerical evaluation of diffraction coefficients. The paper contains a review of scientific work concerning scattering by objects with edges, corners, tips, etc.
TL;DR: In this article, two modifications to a rectangular-patch antenna, suitable for the integration of active devices, are presented, which allow optimal matching of the active device by changing the position, width, and length of the impedance-line transformer.
Abstract: Two modifications to a rectangular-patch antenna, suitable for the integration of active devices, are presented. In the first modification, the impedance inverter was placed in the rectangular opening formed by removing the central part of the patch. This modification allows optimal matching of the active device by changing the position, width, and length of the impedance-line transformer. An oscillating antenna, using this modified patch and a Gunn diode, showed a high EIRP, higher spectral purity, and substantially lower cross-polarization levels, in comparison with the reference active antenna with an unmodified patch. Because of the higher overall Q, this modification is recommended for active-antenna applications with active devices that have a narrower negative-resistance bandwidth. In the second modification, an active device (Gunn diode) was integrated directly into a rectangular opening inside the patch, without the use of a line transformer. This reduced the overall Q of the antenna, thus allowing wide-band frequency tuning by changing the bias voltage. A clear spectrum, with no spurious components of the free-running oscillating antenna, was observed. Radiation patterns in the E and H planes were measured. Low levels of cross-polarization, as for the first modification, were obtained. Injection-locking properties were investigated throughout the tuning range. A relatively wide locking range, with a good locking gain, was achieved. Such a miniaturized wide-band VCO antenna is applicable for integration in injection-locked active arrays, and spatial power combiners.
TL;DR: An overview of ALCOR radar waveforms and resolution capabilities is provided and a system description is provided, including the C-band transmitter, receiver, antenna, and digital systems.
Abstract: Kwajalein Atoll, resting 9/spl deg/north of the equator and 3,500 km southwest of Hawaii, is the location of the United States Army Kwajalein Missile Range (KMR). KMR assets include a wide variety of radars, optical sensors, telemetry, missile-launch equipment, flight safety, and communications. Its radar suite, in particular, includes several highly sensitive one-of-a-kind systems. The ARPA-Lincoln C-Band Observables Radar (ALCOR) is one of four KMR instrumentation radars located on the island of Roi-Namur. Since ALCOR first began operations in 1970, it has provided C-band beacon and wideband metric and signature observations for a wide variety of range-user requirements. ALCOR has the capability to produce two-dimensional range Doppler images of near-Earth-orbiting and reentering objects. Modifications to ALCOR, its current system architecture, and future direction are described in this paper The authors provide an overview of ALCOR radar waveforms and resolution capabilities. A system description is provided, including the C-band transmitter, receiver, antenna, and digital systems.
TL;DR: To a great extent, the material is extracted from class lectures, but it does not suffer from the cryptic style commonly associated with lecture notes.
Abstract: his is an excellent book The preface tells us that “[tlhe text presents the material from a second semestef graduate level course on Estimation offered in the Department of Electrical and Systems Engineering [the] main goal of this course is to convey the knowledge necessary for the evaluation and design of state estimators that operate in a stochastic environment” To a great extent, the material is extracted from class lectures, but it does not suffer from the cryptic style commonly associated with lecture notes
TL;DR: In the IEEE reprint series, Analysis and Design of Planar Microwave Components is concerned with the analysis techniques and applications of planar microwave structures, which are everything from simple transmission lines and power splitters to complex filters, couplers, antennas, and antenna arrays as discussed by the authors.
Abstract: Another in the IEEE reprint series, Analysis and Design of Planar Microwave Components is concerned with the analysis techniques and applications of planar microwave structures, Planar microwave structures are everything from simple transmission lines and power splitters to complex filters, couplers, antennas, and antenna arrays: all realized by forming two-dimensional metallized patterns on a (typically) flat dielectric surface. This text differs somewhat from many reprint collections, in that the editors supplemented the reprints with four chapters of new and original material. This additional material helps unify the presentation, and provides the reader with the breadth and details that often are omitted (for brevity) from journal publications. The book is divided into two sections. The first six chapters contain papers and descriptions of analysis methods and numerical techniques, while the remaining five chapters show how these approaches can be used to analyze specific types of microwave-circuit structures. A brief overview of each of the eleven chapters follows.
TL;DR: In this article, the application of the Newton-Kantorovich and modified-gradient methods to the Ipswich data is considered, where the object is assumed to be an inhomogeneous lossy dielectric cylinder of arbitrary cross section.
Abstract: The present paper considers the application of the Newton-Kantorovich and modified-gradient methods to the Ipswich data. The object is assumed to be an inhomogeneous lossy dielectric cylinder of arbitrary cross section. Both inverse-scattering methods are based on electric-field integral representations. The Newton-Kantorovich technique builds up the solution by solving successively the forward problem and a linear inverse problem. This method needs regularization, and we use either the identity operator or a gradient operator for regularization. The modified-gradient method is iterative, as is the Newton algorithm, but does not involve a linearization at each step of the nonlinear inverse problem. Results of inversions with both methods, on two known impenetrable targets, are discussed.
TL;DR: In this article, a simple and closed-form expression for the E field in sea water is derived from two physical models, which agree but are different: the surface-wave theory and the Fresnel formulas.
Abstract: The problem of receiving VLF electromagnetic fields with an underwater electric antenna is of great interest, especially for military-application purposes. In this study, a simple and closed-form expression for the E field in sea water is derived from two physical models, which agree but are different: the surface-wave theory and the Fresnel formulas. Three configurations of immersed receiving antennas are investigated by means of computer simulations. The scattered electric field and expected measured voltage are computed, using an EFIE [electric-field integral equation], and the method of moments (MoM). Then, an equivalent-circuit model of the underwater antenna is investigated, with a focus on two dominant antenna parameters: the impedance and the voltage measured between the wire terminals. Calculations and computed results are compared with off-shore measurements.
TL;DR: In this article, the authors present an overview of some of the latest antenna-design tools and technology developments, supported by the European Space Agency for space applications, including reflectors, feed systems, and direct-radiating arrays.
Abstract: The environment, as well as the mass and available power limitations specific to space missions, add special constraints. These lead to the use of exotic low-mass, high-stability materials, with advanced mechanical and thermal designs. Also, antenna front ends must be tailored for optimum efficiency and power handling. Researchers and engineers in universities, research institutes, and industrial laboratories, from the 14 member states of the European Space Agency (ESA), together with staff from the European Space Agency's Technology Centre (ESTEC) antenna section and from project teams, have studied and developed software-modeling tools, critical reflector and array technologies, novel antenna architectures, and special measurement techniques to cope with these requirements. This paper presents an overview of some of the latest antenna-design tools and technology developments, supported by ESA for space applications. The following topics are covered reflectors, feed systems, and direct-radiating arrays. Some trends and developments in space antenna requirements and technologies are outlined.
TL;DR: The use of adaptive methods to refine the mesh as needed, for a more efficient use of the computational resources, are discussed.
Abstract: The finite-element method has emerged as an important tool in computational electromagnetics. Accurate solutions require fine meshes, with commensurately large computational requirements. We discuss the use of adaptive methods to refine the mesh as needed, for a more efficient use of the computational resources. Both h-adaptation (smaller elements) and p-adaptation (higher-order elements) are described. Good results have been obtained for energy-related errors within the FEM mesh. However, results for far-field parameters, such as radar (echo) width, are less promising.
TL;DR: The MMET Symposium as mentioned in this paper is devoted to theoretical and mathematical problems in electromagnetic fields, providing a unique forum to hear about what is going on in this field and in many other areas, as well as in the CIS (former USSR) republics.
Abstract: Every even year, our Ukrainian colleagues organize a symposium specifically devoted to theoretical amd mathematical problems in electromagnetic, providing a unique forum to hear about what is going on in this field-and in many other areas, as well-in the CIS (former USSR) republics. Even though participants come mostly ilom Ukraine and Russia, all contributions are presented in English: this is a feature of MMET Symposia, the purpose of which is to foster ties with Western researchers in electromagnetic
TL;DR: The contrast source inversion (CSI) method was used by van den Berg et al. as discussed by the authors to reconstruct the shape, location, and index of refraction of known and unknown scatterers from the measured scattered field data contained in IPS001-IPS008.
Abstract: For pt.II see ibid., vol.39, p.29-32 (1997). We describe results obtained in image reconstruction using the Ipswich data sets IPS009-IPS012. In van den Berg et al. (1995, 1997) and van den Berg and Kleinman (1996), we employed versions of the modified gradient method to reconstruct the shape, location, and index of refraction of known and unknown scatterers, both dielectric and perfectly conducting, from the measured scattered field data contained in IPS001-IPS008. In the present paper, we employ a new inversion method, the contrast source inversion (CSI) method, for the reconstructions. We include here a brief description of the method, given in greater detail in van den Berg and Kleinman. In the case of the new Ipswich experiments, we have 36 angles of incidence, equidistantly distributed around the object. The unknown scatterer is assumed to be located somewhere in a known, bounded, test domain D (taken to be square), and the scattered field is measured on a domain S (taken to be a circle) containing the test domain D in its interior. In the case of the Ipswich experiments, S was taken to be in the far zone of the scattered field, and measurements were made at 18 angles of observation, equidistantly distributed over a semicircle. For each experiment, this semicircle started with the forward-scattering angle.
TL;DR: An overview is presented of the antenna research carried out by the Directorate of Antennas and Integrated Electronics (DAIE) of the Communications Research Centre (CRC), which can be categorized into two groups: antenna-hardware development and electromagnetic-software development.
Abstract: An overview is presented of the antenna research carried out by the Directorate of Antennas and Integrated Electronics (DAIE) of the Communications Research Centre (CRC). The antenna research within the DAIE can be categorized into two groups: antenna-hardware development and electromagnetic-software development. Research in antenna hardware has focused on printed multi-layer arrays, dielectric-resonator antennas, ferrite antennas, active-circuit integration, and low-loss feed networks. Research in electromagnetic software includes the development of three-dimensional transmission-line-matrix (TLM) code, and the application of cellular automata (CA) techniques for the analysis and modeling of antennas, microwave circuits, and general electromagnetic phenomena, such as scattering. This article concentrates on the antenna-hardware research and development within the DAIE. Radiation patterns are considered.
TL;DR: In this article, the authors describe the design and results of low-sidelobe arrays, starting from the measurement of basic slot characteristics in an array simulator, and the realization of a prescribed amplitude distribution, by tapering the slot length, is shown.
Abstract: For a frequency-scanning-radar project, a traveling-wave-array antenna was designed. It employs radiating slots in the narrow wall of a meander-rectangular waveguide, which is milled in a flat metal block. Due to the restriction of the waveguide width, the maximum slot length that could be implemented is less than a half wavelength, i.e., below the resonant length. Although such slots are commonly deemed useless, it is shown that traveling-wave-array antennas can be designed successfully. This paper describes the design and results of low-sidelobe arrays, starting from the measurement of basic slot characteristics in an array simulator. The realization of a prescribed amplitude distribution, by tapering the slot length, is shown. The creation of phase errors, due to the reactive nature of the slots, and the associated pattern-degradation effects, are discussed in detail.
TL;DR: This paper reviews recent progress, and compares several recent derivative-extraction methods: local smoothing, superconvergent-patch recovery (SPR), and methods based on Green's second identity.
Abstract: Accurate derivative calculation is a key process in computational electromagnetics. Differentiation is required for graphic display, a posteriori error estimation, automatic mesh refinement, and result post-processing. The choice of method depends on the accuracy required, and on the order of derivatives to be computed. This paper reviews recent progress, and compares several recent derivative-extraction methods: local smoothing, superconvergent-patch recovery (SPR), and methods based on Green's second identity. The SPR approach of Zhu and Zienkiewicz (see Finite Elements in Analysis and Design, vol.19, p.1123, 1995) has been extended in several ways to yield good accuracy at low cost, but it can only produce first derivatives. The Green's identity methods of Silvester and Omeragic (see International Journal of Applied Electomagnetics in Materials, vol.4, p.123-136, 1993) are computationally expensive, but extremely accurate, even for third and fourth derivatives. Representative numerical results illustrate the methods discussed.
TL;DR: The new results are based on a generalization of the classical concepts of scalar image impedance, and of a scalarimage-transfer function for two-port networks, to the new concepts of multidimensional image-impedance matrix, andOf multiddimensional image- transfer function for linear multi-port Networks.
Abstract: Recent, very general and fundamental results in the theory of electrically large microwave networks lead to new, advanced designs of high-efficiency beam-forming networks, for high-directivity electronically-steered phased arrays. On the basis of the rigorous new results, the beam-forming networks of electronically-steered phased arrays can be simultaneously impedance matched to any given set of radiating elements on one side, and to any given set of mutually-coherent, phase- and amplitude-controlled microwave sources on the other. Further, the impedance match attained in transmission also holds in reception, as long as the set of mutually-coherent receivers used has the same internal impedances as the set of sources used. The impedance match attained accounts simultaneously for both the electromagnetic proximity coupling between all the radiating array elements, and for any given internal cross-coupling of the set of sources, in transmission, or of the set of receivers, in reception. The resulting impedance match is totally independent from the amplitude and phase settings of the sources, in transmission, and from the direction of the incoming beam, in reception, completely suppressing the notorious array-blindness effect for all beam directions. Further, beam-forming networks can also be designed with prescribed transmission responses-besides a prescribed impedance match-in both the transmission and reception modes, and with a number of beam-steering control components that is much smaller than the number of array elements.