Showing papers in "IEEE Antennas and Propagation Magazine in 1999"
TL;DR: Some important properties of fractal arrays are introduced, including the frequency-independent multi-band characteristics, schemes for realizing low-sidelobe designs, systematic approaches to thinning, and the ability to develop rapid beam-forming algorithms by exploiting the recursive nature of fractals.
Abstract: A fractal is a recursively generated object having a fractional dimension. Many objects, including antennas, can be designed using the recursive nature of a fractal. In this article, we provide a comprehensive overview of recent developments in the field of fractal antenna engineering, with particular emphasis placed on the theory and design of fractal arrays. We introduce some important properties of fractal arrays, including the frequency-independent multi-band characteristics, schemes for realizing low-sidelobe designs, systematic approaches to thinning, and the ability to develop rapid beam-forming algorithms by exploiting the recursive nature of fractals. These arrays have fractional dimensions that are found from the generating subarray used to recursively create the fractal array. Our research is in its infancy, but the results so far are intriguing, and may have future practical applications.
441 citations
TL;DR: The semi-inversion method as mentioned in this paper is a family of methods based on conversion of a first-kind or strongly-singular second-kind integral equation to a second kind integral equation with a smoother kernel, to ensure pointwise convergence of the usual discretization schemes.
Abstract: We discuss the foundations and state-of-the-art of the method of analytical regularization (MAR) (also called the semi-inversion method). This is a collective name for a family of methods based on conversion of a first-kind or strongly-singular second-kind integral equation to a second-kind integral equation with a smoother kernel, to ensure point-wise convergence of the usual discretization schemes. This is done using analytical inversion of a singular part of the original equation; discretization and semi-inversion can be combined in one operation. Numerous problems being solved today with this approach are reviewed, although in some of them, MAR comes in disguise.
204 citations
TL;DR: It is shown that the computational cost of performing a surface-scattering analysis, using two-level and multilevel PWTD-enhanced MOT schemes, scales much more favorably than that of classical MOT schemes.
Abstract: This article describes a plane-wave time-domain (PWTD) algorithm that facilitates the fast evaluation of transient wave fields produced by surface scattering. The algorithm presented relies on a Whittaker-type expansion of transient fields in terms of propagating plane waves. The incorporation of the PWTD scheme into existing matching-on-in-time- (MOT-) based integral-equation solvers is elucidated. It is shown that the computational cost of performing a surface-scattering analysis, using two-level and multilevel PWTD-enhanced MOT schemes, scales as O(N/sub t/N/sub s//sup 1.5/ log N/sub s/) and O(N/sub t/N/sub s/log/sup 2/N/sub s/), respectively, when the surface source density is represented by N/sub s/ spatial and N/sub t/ temporal samples. Hence, the computational cost of the proposed algorithms scales much more favorably than that of classical MOT schemes, which scale as O(N/sub t/N/sub s//sup 2/). Therefore, PWTD-enhanced MOT schemes make possible the analysis of broadband scattering from structures of unprecedented dimensions.
174 citations
TL;DR: In this paper, a full-wave model is developed for electromagnetic scattering from buried and surface land mines (both conducting and plastic), taking rigorous account of the lossy, dispersive, and potentially layered properties of soil.
Abstract: A full-wave model is developed for electromagnetic scattering from buried and surface land mines (both conducting and plastic), taking rigorous account of the lossy, dispersive, and potentially layered properties of soil. The (polarimetric) theoretical results are confirmed via synthetic-aperture radar (SAR) measurements, performed using the US Army Research Laboratory's BoomSAR, with which fully polarimetric ultra-wide-band (50-1200 MHz) SAR imagery is produced. The SAR system is used to acquire a large database of imagery, including a significant distribution of naturally occurring clutter. Several techniques are used for mine detection with such data, including several detectors that are based on target features gleaned from the modeling, as well as a matched-filter-like detector that directly incorporates the target signatures themselves. In addition, the theoretical model is used to predict wave phenomenology in various environments (beyond the limited range of parameters that can be examined experimentally). Since the efficacy of radar-based subsurface sensing depends strongly on the soil properties, we perform a parametric study of the dependence of such on the target RCS, and on possible landmine resonances.
153 citations
TL;DR: The method underlying CINDOOR is a flexible approach to the propagation process, allowing analysis of indoor and outdoor environments and the interaction between them, and is based on a full three-dimensional implementation of GO/UTD.
Abstract: This paper presents the program CINDOOR. This program is an engineering tool for aiding in the design, planning, and effective implementation of wireless systems in general enclosed spaces. The method underlying CINDOOR is a flexible approach to the propagation process, allowing analysis of indoor and outdoor environments and the interaction between them. The method is based on a full three-dimensional implementation of GO/UTD. Ray tracing is efficiently carried out by combining image theory with binary space partitioning algorithms. The space-time distribution of the electromagnetic field is processed to obtain a set of magnitudes that form a basis for planning a wireless system: coverage (mean power), fading statistics, power delay profile and associated parameters, such as the rms delay spread and the coherent bandwidth.
125 citations
TL;DR: The finite-difference time-domain is the most often used method for evaluation of electromagnetic fields in human tissue, and extensive investigations are shown of the resultant SAR due to the number of electric field components used in field averaging, and the volume of air within the cube.
Abstract: The finite-difference time-domain (FDTD) is the most often used method for evaluation of electromagnetic fields in human tissue. This is of particular importance for compliance testing of portable telephones. The specific absorption rate (SAR) averaged over 1 or 10 g tissue mass is required by regulations not to exceed a prescribed value. A computer algorithm is developed for post-processing the FDTD data. This algorithm can be used for uniform as well as graded meshes, while the required cubical shape is maintained. Extensive investigations are shown of the resultant SAR due to the number of electric field components used in field averaging, and the volume of air within the cube. The latter is easily controlled in the algorithm, but the regulations on the permissible SAR do not specify it at the present time.
96 citations
TL;DR: In this article, the authors present an overview of the design and measured performance of some examples of dielectric lenses that can be used in typical scenarios of wireless broadband communication systems, and also address the radio coverage produced by these antennas.
Abstract: Dielectric-lens antennas are effective at producing highly shaped beams that can enhance the performance of wireless broadband communication systems. Beam shaping is used to reduce multipath interference, which causes fading and decay spread, and to enhance gain, so that the received power level is compatible with the requirements of high-data-rate transmission. This paper presents an overview of the design and measured performance of some examples of dielectric lenses that can be used in typical scenarios of wireless broadband communication systems. The paper also addresses the radio coverage produced by these antennas. The lenses are based on a single basic configuration where the feed is embedded in the lens body. This antenna configuration is flexible enough to accommodate different target beam-shaping specifications.
82 citations
TL;DR: In this article, a series of 550 mm diameter linearly polarized Ku-band prototype antennas were constructed to experimentally investigate the efficiency of reflection cancellation and beam squinting on the antenna.
Abstract: The standard linearly polarized radial-line slot-array (RLSA) antenna exhibits poor return loss as seen by its coaxial feed. This paper describes techniques that improve the poor return-loss performance of this antenna, by using two interchangeable methods: i) reflection-canceling slots on the front and back surface of the antenna, and ii) beam squinting. A series of 550 mm diameter linearly polarized Ku-band prototype antennas were constructed to experimentally investigate the efficiency of each of these methods. In order to cut experimental costs, initial radiation-pattern modeling was performed theoretically, and then prototypes were developed using inexpensive aluminum foil. Measurements of the developed prototypes indicated that both the reflection-canceling and beam-squinting methods provided a substantial improvement in return loss over the desired frequency band.
81 citations
TL;DR: In this paper, simplified design and analysis equations for multiple-beam reflector antennas based on the Gaussian-beam analysis of the primary and secondary patterns are presented for the quick design and performance analysis in terms of the coverage-area directivity and the inter-beam isolation of multiplebeam antenna systems.
Abstract: Simplified design and analysis equations are presented for multiple-beam reflector antennas based on the Gaussian-beam analysis of the primary and secondary patterns. The derived equations are useful for the quick design and performance analysis in terms of the coverage-area directivity and the inter-beam isolation of multiple-beam antenna systems. Results of the analysis given in this paper agree well with rigorous computations based on physical-optics analysis of the reflector-antenna radiation patterns. Extension of the analysis to multiple-beam lens antennas, and to shaped/contoured-beam antennas, is also presented.
79 citations
TL;DR: In this article, the radiation and scattering patterns of three inhomogeneous dielectric lenses: the Luneburg (1944), the Maxwell fish-eye (1860), and the Eaton-Lippmann (1952) lenses are presented.
Abstract: This article presents the radiation and scattering patterns, and the interior field distributions, of three inhomogeneous dielectric lenses: the Luneburg (1944), Maxwell fish-eye (1860), and Eaton-Lippmann (1952) lenses. The purpose is to provide a picture of wave propagation through these lenses. A better understanding of the field picture, especially the nature of the focal points, is helpful to the practical design of the lenses.
69 citations
TL;DR: The author has used rotation matrices to find the patterns with elements in a conformal array that requires one to rotate not only the direction, but the polarization directions, as well.
Abstract: Discusses various uses of rotation matrices. The author has used rotation matrices to find the patterns with elements in a conformal array that requires one to rotate not only the direction, but the polarization directions, as well. A second useful thing to do with rotation matrices is to analytically rotate objects in space. In computer graphics, it may be neccessary to rotate the object. Many computer graphics texts have useful discussions of object rotations using rotation matrices. A third related use of rotation matrices is to understand antenna positioners. One can describe the rotations of a positioner by rotation matrices, and calculate the effects of rotation not only on the directing of the antenna, but on the polarization directions, as well.
TL;DR: In this paper, a simple procedure for the design of classical displaced-axis dual-reflector antennas is given, using four geometric input parameters, a set of equations is derived to find the remaining geometric parameters, fully defining the systems.
Abstract: A simple procedure for the design of classical displaced-axis dual-reflector antennas is given. Using four geometric input parameters, a set of equations is derived to find the remaining geometric parameters, fully defining the systems. This initial geometry provides a good starting point for any optimization process.
TL;DR: In this article, the authors presented an overview of two different types of smart antenna systems: the tracking-beam array (TEA) and the switching beam array (SEA) systems.
Abstract: This paper presents an overview of two different types of smart antenna systems: the tracking-beam array (TEA) and the switching-beam array (SEA) systems. A conceptual description of each system is given, to analyze the inherent advantages and disadvantages of the two systems. The array systems shown in this paper are aimed at code-division multiple-access (CDMA) mobile communications. The desired beam pattern can be obtained from the weight vector through the scalar product between the weight vector and the signals, because the in-phase and quadrature components of the baseband signal preserve the magnitude and phase of the signal at each antenna element. Since the weight vector of the TEA system is computed from the solution of the eigenvector corresponding to the largest-magnitude eigenvalue, the TEA system outperforms the switching-beam array system when the desired signal is sufficiently larger than each of the interfering signals, because of the high processing gain. As the ratio of the power of the desired signals to the power of the interfering signals becomes lower, the superiority in the performance of the two systems is reversed.
TL;DR: The full algorithm for predicting propagation and cellular characteristics to increase the accuracy of radio and cellular maps is presented.
Abstract: The propagation channel for UHF/X-band waves in the city is modeled for two typical cases in the urban scene: (a) by regularly distributed rows of buildings placed on a flat terrain; and (b) by an array of randomly distributed buildings placed on rough terrain. The law of distribution of buildings in both cases is assumed to be Poisson. The loss characteristics in such urban propagation channels, as well as the co-channel interference parameter, the carrier-to-interference ratio (C/I), are investigated. In case (a), the three-dimensional multi-slit waveguide model is used for LOS conditions, and the two-dimensional multi-diffraction model is used for NLOS conditions. In case (b), the statistical parametric model of wave propagation is used, including single and multiple scattering effects, diffraction from buildings' roofs, the actual built-up relief, and various positions of receiver and transmitter antennas on rough terrain. The full algorithm for predicting propagation and cellular characteristics to increase the accuracy of radio and cellular maps is presented.
TL;DR: The Third Annual Special Session on Image Reconstruction T u s i n g R:al Data was conducted at the AP-S/URSI Intemational Symposium, held July 13-18, 1997, in Montreal, Canada.
Abstract: he “Third Annual Special Session on Image Reconstruction T u s i n g R:al Data” was conducted at the AP-S/URSI Intemational Symposium, held July 13-18, 1997, in Montreal, Canada. The session was well-attended, featuring seven invited papers, as well as a walk-on participant. For those interested in detailed descriptions of our measurement facility and our FTP server, see refirences [l] and [2]. This session was the last one in which my respected colleague and friend, Professor Ralph Kleinman, participated. As you know, Ralph passed away in 1998, much too soon. I first met Ralph in 1975, when he was a visiting Professor at the Microwave Physics Laboratory of the Air Force Cambridge Research Laboratories. We stayed in touch after he returned to Delaware, and through the years he became somewhat of a mentor-at-adistance. Ralph and my thesis advisor, Professor Mike Fiddy at the University of Massachusetts, Lowell, were both heavily involved in inverse scattering, and their combined influence was instrumental in my choice of a thesis topic. Ralph first suggested that I post scattering data on the Internet, and then convinced me that a contest with mystery targets would not be shunned by inverse scatterers. I benefited from his council and his sense of humor for 23 years, and I will miss him.
TL;DR: In this paper, the authors discuss several basic features related to the transient radiation of electromagnetic waves by straight thin-wire antennas, from a physical point of view, and present a theoretical analysis of these features.
Abstract: The paper discusses, from a physical point of view, several basic features related to the transient radiation of electromagnetic waves by straight thin-wire antennas.
TL;DR: In this paper, the authors present an overview of active array antennas, system-level nonlinear effects in such antennas, and their modeling and simulation techniques, in comparison with passive array antennas.
Abstract: This paper presents an overview of active array antennas, system-level nonlinear effects in such antennas, and their modeling and simulation techniques. Advantages of active array antennas, in comparison with passive array antennas, are discussed. The influence of nonlinear distortions and interference in active antennas on the overall system performance is considered. Modeling and simulation techniques that can be applied to active array antennas are substantially different from those used for circuits and systems. Analytical and numerical techniques are used for the analysis of active antennas, with the prevailing use of numerical techniques at the present time. Electromagnetic-level and circuit-level simulation techniques are discussed. System-level simulation techniques are considered in detail, with special emphasis on their application to active array antennas. The "instantaneous" quadrature technique is proposed as an effective tool for numerical simulation of active arrays over wide frequency and dynamic ranges in a computationally-effective way.
TL;DR: A three-dimensional, automatically adjustable, non-uniform orthogonal-mesh generator, AutoMesh, developed using a Windows application-development package, Microsoft Visual Basic, which can efficiently produce geometrical and material data files for a complex electromagnetic configuration.
Abstract: In this article, we introduce a three-dimensional, automatically adjustable, non-uniform orthogonal-mesh generator, AutoMesh, developed using a Windows application-development package, Microsoft Visual Basic. The developed mesh-generating package can efficiently produce geometrical and material data files for a complex electromagnetic configuration that serve as inputs to a generalized non-uniform finite-difference time-domain (FDTD) Maxwell's equations solver. In addition, the fruitful graphical functions of the package insure not only the accuracy of the generated data files, but also the ease of mesh generation for complex objects. Herein, we first present the algorithm of mesh generation, and then illustrate graphical features of the package.
TL;DR: FASANT is a computer tool for the analysis of antennas on-board satellites, ships, aircraft, and other complex bodies that can obtain far-field patterns, field levels at points near the structure, and can calculate the mutual coupling between antennas or between array elements.
Abstract: FASANT is a computer tool for the analysis of antennas on-board satellites, ships, aircraft, and other complex bodies. The structure under analysis, which can be metallic or dielectric (with and/or without losses), must be modeled by plane and/or curved surfaces. The geometrical input files are in DXF format, and can be generated by the most commonly used computer-aided geometrical-design (CAGD) tools. The code can also be applied to the analysis of arrays and arbitrarily shaped reflectors. The kernel of the code is based on the uniform theory of diffraction (UTD). Special algorithms have been developed to speed up the ray-tracing computation for both flat and curved surfaces. FASANT can obtain far-field patterns, field levels at points near the structure, can calculate the mutual coupling between antennas or between array elements, and can show each ray-tracing mechanism.
TL;DR: In this article, the authors present a practical and pragmatic introduction to radio propagation for fixed and mobile communications, and provide numerous entries for the CCIR (ITU-R) reports available and ready for use.
Abstract: All in all, the book is well written, and provides numerous entries for the CCIR (ITU-R) reports available and ready for use. Every chapter starts of with an introduction, and a summary of the chapter is given at its end. Except for the overlooked subjects (site shielding, deterministic modeling of propagation) the subject matter is well covered. The book provides what its title says. It is a practical and pragmatic introduction to radio propagation for fixed and mobile communications.
TL;DR: In this paper, an L-band planar, multi-layer circular array for possible use with the Australian geostationary mobile-satellite communications system, Mobilesat/sup TM, is presented.
Abstract: This paper presents the design and development of an L-band planar, multi-layer circular array for possible use with the Australian geostationary mobile-satellite-communications system, Mobilesat/sup TM/. Twelve single-feed, stacked aperture-coupled microstrip patches, interleaved with low-cost dielectric foam and arranged in two rings, form the array. The beam-forming network is comprised of three-bit phase shifters, which are located under the antenna elements. Low-cost UHF-band switching diodes were used to minimize the developmental cost of these phase shifters. In order to make the diodes operational at L-band, an LC compensation technique was applied to the diodes to tune out parasitic reactance. Experimental results for individual antenna elements and phase shifters, followed by the results for the entire array, are presented. The indoor testing results for the manufactured antenna showed that the array satisfies the specifications of Mobilesat/sup TM/. This was also confirmed by outdoor field trials with a NEC S1 transceiver terminal.
TL;DR: In this article, measurements were made of radio wave attenuation through a cottonwood plantation at the University of Illinois at Urbana-Champaign, on a number of frequencies between 27 and 411 MHz.
Abstract: In 1997 and 1998, measurements were made of radio wave attenuation through a cottonwood plantation at the University of Illinois at Urbana-Champaign, on a number of frequencies between 27 and 411 MHz. Based on these measurements, an empirical formula that describes radio wave attenuation was developed.
TL;DR: The selection of the position and monopulse controllers for the improved tracking accuracy is described, and the results of linear and non-linear simulations are presented to confirm that servo performance will meet the requirements.
Abstract: Ka-band (32 GHz) monopulse tracking has been chosen for the upcoming NASA missions. This decision requires an increased pointing accuracy for the Deep Space Network antenna servo systems that can be maintained in a noisy environment. The noise sources include wind gusts, encoder imperfections, and receiver noise. This article describes the selection of the position and monopulse controllers for the improved tracking accuracy, and presents the results of linear and non-linear simulations to confirm that servo performance will meet the requirements.
TL;DR: In this paper, a common formula for directivity, given beamwidths, and modifications needed to improve the accuracy when the Taylor single-parameter distribution is known is given.
Abstract: Starting with a common formula for directivity, given beamwidths, the author gives the modifications needed to improve the accuracy when the distribution is known. Also included is a nomograph that shows the parameters of the Taylor single-parameter distribution, and allows trade studies versus the sidelobe level.
TL;DR: In this paper, the authors used the Ipswich data to validate the approximate back-propagation (ABP) methods, which were originally developed to identify the shape of acoustic scatterers in the resonance region.
Abstract: For pt.1 see ibid., vol.41, no.1, p.34-51 (1999). The Ipswich data provide a unique opportunity for the validation of the approximate back-propagation (ABP) methods, which were originally developed to identify the shape of acoustic scatterers in the resonance region. These methods rely on a heuristic relationship, i.e., ABP, between the expansion coefficients that represent the scattered wave in the far zone and those on the obstacle boundary, /spl Gamma/. The unknown is the shape-parameter vector, /spl psi//spl I.oarr//spl isin//spl Psi//sub ad/, the admissible set. The objective function to be minimized is the L/sup 2/(/spl Gamma/)-norm of the boundary defect. In the vertical-polarization case, ABP consists of an affine map, which is easy to derive. Its ingredients are arrays of inner products in L/sup 2/(/spl Gamma/), where outgoing cylindrical wave functions are involved. The corresponding numerical results, based on the IPS001VV data, are satisfactory. The attraction domain of the expected solution, the reference obstacle (a disk), is numerically determined by varying the initial conditions in a wide subset of /spl Psi//sub ad/. Reconstruction seems to be unique, although no uniqueness condition is known for the obstacle. In the horizontal-polarization case, ABP relies on vector harmonic functions in a cylindrical geometry. The complexity of the algorithm is higher. Results based on the TPS001HH set are summarized. Although the numerical solution does not show any focal minimum other than the reference obstacle, the corresponding attraction domain is smaller than in the vertical-polarization case.
TL;DR: In this article, the performance of a beam waveguide antenna at X-band and Ka-band microwave frequencies was evaluated at the Goldstone DSS-13 research and development (R&D) beam-waveguide antenna between December, 1993 and November, 1995.
Abstract: New antennas for the NASA Deep Space Network (DSN) have been built to replace the aging antennas of older designs for deep-space communications. These new antennas incorporate a new dual-shape design as well as a beam waveguide (BWG), which utilize a series of additional secondary mirrors to relocate the focal point into a stationary room below the main reflector. The advantages of using such a design include increased isolation of the feed package from outside environmental factors, such as moisture, wind, and temperature changes; and ease of access to the equipment for maintenance, troubleshooting and repair purposes. This article reports on the performance of a beam waveguide antenna at X-band and Ka-band microwave frequencies. The Ka-band antenna performance experiment (KaAP) antenna-efficiency measurements presented in this article were acquired at the Goldstone DSS-13 research and development (R&D) beam-waveguide antenna between December, 1993, and November, 1995. The measured antenna efficiency and ground-station figure-of-merit (gain divided by operating system noise temperature) as a function of elevation angle and their uncertainties are presented. Also described are the station configuration, the measurement technique, the modeling used in the analysis processing, and the historical evolution of the DSS-13 Ka-band antenna-efficiency measurements as progressive improvements and configuration changes were implemented.
TL;DR: In this article, the far-field radiation pattern equations for the pyramidal-horn antenna are derived and compared to measured data, and a Mathcad simulation is presented to provide a comprehensive approach for the prediction of the far field radiation pattern.
Abstract: In this paper, the far-field radiation-pattern equations for the pyramidal-horn antenna are derived and compared to measured data, and a Mathcad simulation is presented. The mathematical formulation given provides a comprehensive approach for the prediction of the far-field radiation pattern. Furthermore, the formulation can be modified and implemented with Mathcad for other types of aperture antennas.
TL;DR: In this paper, in-home propagation measurements, in the frequency range of 400, 860, and 2400 MHz, are evaluated for single, narrow-band applications of one-way domestic mobile alarm systems.
Abstract: In-home propagation measurements, in the frequency range of 400, 860, and 2400 MHz, are evaluated for single, narrow-band applications of one-way domestic mobile alarm systems. In particular, the influence of multipath effects is investigated.
TL;DR: In this paper, an artificial-neural network (ANN) method is employed to predict the maximum useable frequency (MUF) in the region of the South China Sea.
Abstract: In this paper, an artificial-neural-network (ANN) method is employed to predict the HF-communication MUF (maximum useable frequency) in the region of the South China Sea. Historical observation data of f/sub 0/F/sub 2/ from six ionospheric observatories around the South China Sea are used to train the network. The comparison of ANN predictions and International Reference Ionosphere (IRI) models with the observations shows that the ANN predictions are closer to the observed results than are the IRI predictions.
TL;DR: In this article, it has been demonstrated that the high-frequency physical optics-based code CADDSCAT can utilize trimmed curved surfaces and a significant potential savings in design person-hours and a reduction in design cycle time has been made possible.
Abstract: It has been demonstrated that the high-frequency physical optics-based code CADDSCAT can utilize trimmed curved surfaces. Validations for canonical targets were presented. A significant potential savings in design person-hours and a reduction in design cycle time has been made possible. This, in turn, allows for more alternative, innovative designs.