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ABSTRACT: The present work proposes a novel case-based reasoning system for fault diagnosis in moderate or large linear antenna arrays. This system identifies the set of elements that are most likely to be defective, helping to significantly reduce the computational costs of their detection (e.g., using an optimization technique such as a genetic algorithm).
IEEE Antennas and Propagation Magazine 09/2008; · 0.97 Impact Factor
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ABSTRACT: We review and formalize the mathematical background of time-modulated linear arrays (TMLAs); then, a number of issues are examined. First, for signal transmission applications, restrictions to the frequencies involved in the procedure are highlighted. Second, the sideband power losses associated to the technique are thoroughly examined, introducing a coefficient appropriate to evaluate the efficiency of the procedure. Finally, a closed form expression for the total power associated to sideband radiation is obtained, very convenient for the implementation of real-time optimization of the system. Relevance of additional research on the subject is highlighted.
IEEE Transactions on Antennas and Propagation 07/2008; · 2.15 Impact Factor
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ABSTRACT: Footprint patterns can be efficiently synthesized by means of planar arrays with hundreds or thousands of elements: an efficient combination of Woodward-Lawson and Orchard-Elliott-Stern roots optimization procedure is suggested. This hybrid technique is applied to a footprint covering Europe by using planar arrays with isotropic elements and linearly polarized circular patches. The proposed method keeps under control both the side lobe and ripple level of the synthesized pattern.
IEEE Transactions on Antennas and Propagation 03/2008; · 2.15 Impact Factor
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ABSTRACT: A new antenna pattern synthesis technique that allows the design of large planar antenna array radiating footprint patterns of a specified boundary with controlled ripple and sidelobe levels is presented. The method synthesises the desired footprint as a composition of a set of circular Taylor patterns appropriately weighted with the samples of the pattern obtained after stretching or shrinking a continuous circular aperture distribution developed by the Elliott-Stern method. A footprint of continental Europe radiated by a planar array with a large number of elements shows the technique's performance. The synthesis procedures were completed in about 1 s using a desktop computer.
Electronics Letters 02/2008; · 0.96 Impact Factor
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ABSTRACT: Combination of simulated annealing methods with Kim and Elliott's generalization of the Tseng-Cheng distribution allows rapid synthesis of planar arrays with rectangular lattices, circular boundaries and very low dynamic range ratio that generate sum patterns with satisfactory characteristics. One of the applications of this method is the synthesis of a multibeam coverage on Europe.
Antennas and Propagation, 2007. EuCAP 2007. The Second European Conference on; 12/2007
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ABSTRACT: The purpose of this presentation is to formalize the full mathematical background of time-modulated linear arrays (TMLAs), in particular to determine the total losses due to their sideband radiation, once the time-modulation of their elements has been specified. Two modulation shapes (rectangular and trapezoidal pulses) and their corresponding power losses -given in closed form-, are considered and compared. The presented results allow evaluation of their advantages and drawbacks, thus leading to the optimal design of the time-modulation configuration.
Antennas and Propagation, 2007. EuCAP 2007. The Second European Conference on; 12/2007
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ABSTRACT: In this work, several numerical and analytical techniques of fault diagnosis, that require the use of samples of the damaged radiation pattern, have been tested and compared. Firstly, we show that the Woodward-Lawson technique is useful to locate the faulty elements, by calculating the excitations of the defective array with the use of samples at appropriate far field angular positions. On the other hand, numerical methods, such as genetic algorithms, neural networks and case-based reasoning (CBR) systems, have been implemented to achieve directly the configuration of defective elements.
Antennas and Propagation, 2007. EuCAP 2007. The Second European Conference on; 12/2007
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ABSTRACT: The proposed quasi-analytical method undertakes the shaping of a desired footprint as a composition of several phi-symmetric circular Taylor patterns exhibiting flat-topped beams. The final pattern is obtained after sampling the circular aperture that is obtained for rectangular-grid planar arrays. A triangular-shaped footprint and a footprint of continental Europe, radiated by planar arrays with moderate and large numbers of elements, show the technique's performance.
IEEE Antennas and Propagation Magazine 11/2007; 49(5):105-112. · 0.97 Impact Factor
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ABSTRACT: Antenna pattern reconfigurability is considered as a major issue for satellite communications. Satellite operators are willing to optimise the overall capacity of their spacecraft fleet. This requires the capacity of traffic reassignment either just before launch or preferably in flight. Antenna array pattern reconfiguration is usually achieved by changing the relative amplitudes and/or phases of the excitations of its radiating elements. However, this approach often requires the design of beam-forming networks of considerable complexity [1-3]. In this communication two innovative methods, based on global optimization techniques, for dipole antenna arrays beam configuration are presented.
Antennas and Propagation Society International Symposium, 2007 IEEE; 07/2007
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ABSTRACT: The design of a number of new antennas that radiate linearly polarized toroidal beams is described. The developed procedures are based on the use of a method of moments commercial software tool. Several numerical examples, working at WLAN communication frequencies, are derived and analyzed. Two experimental prototypes validate the numerical results
IEEE Transactions on Antennas and Propagation 03/2007; · 2.15 Impact Factor
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ABSTRACT: Avery fast technique that allows the synthesising of arbitrary footprint patterns by using conformal arrays with many radiating elements is described. This method is based on a combination of Woodward-Lawson and Elliott-Stern techniques, and it was applied to the synthesis of a triangular footprint generated by 657 axial dipoles placed on a cylindrical surface, obtaining acceptable ripple and sidelobe levels.
Electronics Letters 02/2007; · 0.96 Impact Factor
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ABSTRACT: In this letter, the authors propose an optimization method based on the genetic algorithm (GA) to reconfigure a linear array of vertical half-wavelength dipole antennas to generate two patterns with minimum active impedance variation when the antenna switches from one pattern to other in the presence or absence of a ground plane behind the array. The problem is to find a fixed voltage amplitude distribution that generates two broadside symmetrical beams in the horizontal plane: a pencil beam with zero phases and a flat-top beam with phases in the range from -180deg to +180deg. Mutual coupling effect is taken into account via open circuit mutual impedance matrix
IEEE Antennas and Wireless Propagation Letters 01/2007; · 1.37 Impact Factor
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ABSTRACT: It is shown here, by numerical simulation, that the Moore¿Penrose matrix pseudo¿inversion technique can be applied to retrieve the excitation distribution of a planar array of parallel dipoles with faulty elements, by measuring its near zone complex radiated field at discrete points. Failures on voltages and currents of several elements, as well as systematic amplitude or random (in amplitude or phase) measurement errors, are considered in the simulation. In all cases, mutual coupling between dipoles is taken into account. The scanning surfaces selected to obtain the field values are those customarily used in practical measurement systems: a plane (parallel to the array), a hemicylinder and a hemisphere. The technique can be used as a very reliable alternative for diagnostics of planar arrays in general, and of planar arrays of dipoles in particular. Several examples are worked out, and their results are presented throughout this paper.
Antennas and Propagation, 2006. EuCAP 2006. First European Conference on; 12/2006
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ABSTRACT: Some new antennas that radiate linearly polarized toroidal beams are presented. Two prototypes have been constructed. Their design procedure is based on the use of a method of moments commercial software tool. Very accurate toroidal beams are obtained with large operating relative bandwidths - up to almost 24% in one of the models. Fairly good agreement between calculations and measurements were obtained.
Antennas and Propagation, 2006. EuCAP 2006. First European Conference on; 12/2006
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09/2006; 626:518.
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ABSTRACT: This paper describes a new way of applying the Woodward-Lawson method in order to avoid its limitations concerning pattern performance. The proposed method obtains the Woodward-Lawson beam coefficients by sampling a previously synthesized optimal pattern using the Orchard-Elliott method, what provides the advantages of both synthesis methods. This work also discusses new insights about the multiplicity of solutions in the Woodward-Lawson method
Antennas and Propagation Society International Symposium 2006, IEEE; 08/2006
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ABSTRACT: In this paper, time modulation is applied to a small number of elements of a linear array that radiates either sum or difference patterns, in order to take control over their sidelobe levels. The simulated annealing (SA) technique helps to obtain the optimum time pulses applied to such elements in terms of sideband minimization. © 2006 Wiley Periodicals, Inc. Microwave Opt Technol Lett 48: 829–832, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.21489
Microwave and Optical Technology Letters 03/2006; 48(5):829 - 832. · 0.62 Impact Factor
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ABSTRACT: An innovative method for linear arrays beam reconfiguration is presented. This pattern reconfigurability is achieved by a mechanical displacement of a parasitic array located in front of an active one. Two worked examples that use parallel dipoles are presented.
Electronics Letters 03/2006; · 0.96 Impact Factor
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ABSTRACT: A method for synthesizing footprint patterns radiated by planar reflectors made of a large number of reflecting elements is presented. It is an extension to phase-only synthesis of a previous method that uses the modified Taylor expressions for circular apertures to provide good non-ϕ-ϕ-symmetric patterns. The possibility of selecting any kind of amplitude distribution allows the synthesis of patterns radiated for planar reflectarrays including those with an offset feed. As example, a footprint pattern fitting South America and Miami City was synthesized for a rectangular-grid circular boundary 3228-element reflectarray fed by an offset horn.
Applied Electromagnetics and Communications, 2005. ICECom 2005. 18th International Conference on; 11/2005
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ABSTRACT: Here, we revisit a textbook example of how to design a dipole array and its feed network. The effects of mutual coupling are taken into account, so that a desired set of in-phase excitations is fed to the antenna and radiated efficiently. A MATLAB M-code program, implementing the procedure and plotting the resulting radiation power pattern, is also provided.
IEEE Antennas and Propagation Magazine 11/2005; · 0.97 Impact Factor
