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Antennas and Propagation Magazine, IEEE

Issue 4 • Date Aug. 2002

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Displaying Results 1 - 16 of 16
  • Stochastic versus deterministic models in the analysis of communication systems

    Publication Year: 2002 , Page(s): 40 - 50
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (868 KB) |  | HTML iconHTML  

    When trying to analyze a complex communication system, scientists often apply concepts from stochastic modeling and analysis to obtain a description of the system, frequently assuming that this will supplement our knowledge and improve our understanding. The philosophy is to obtain a result that would occur on the average, when this system is working under normal conditions. However, we must consider the fact that the introduction of probability in communication-system analysis often involves invoking certain assumptions and additional information about the system, which may not be valid. Hence, under these circumstances one may obtain a result that may not be commensurate with the conceived communication system. The objective of this paper is to highlight the basic assumptions that are invariably associated with the signal analysis in a system using stochastic analysis, and the introduction of probabilistic methods. Surprisingly, in many cases, analysis using stochastic methods may provide results equivalent to those obtained using deterministic methods. Examples are presented to illustrate our approach, and to explain the basic assumptions and formulate the mathematical framework associated with a stochastic analysis. We also demonstrate the equivalence between a random and a deterministic process, and under what conditions they approach the Cramer-Rao bound. Analysis using stochastic models to describe a system may be superior to a deterministic description. However, such a characterization comes with a large cost: namely, one must have more definitive knowledge about the system, knowledge that is often unavailable. For convenience, with the application of a random model, the concepts of stationarity and ergodicity are used to simplify the mathematical analysis of measured data. It is shown that the introduction of ergodicity in probability is similar to a deterministic analysis of a single waveform, and, in both cases, characterizes the entire underlying mathem- tical agenda. An example is presented to illustrate the salient features of an ergodic process as opposed to a deterministic process. It is seen that for practical problems, it might be easier and more relevant to introduce a deterministic model and to then carry out a stochastic analysis. However, this may not be practical, since the underlying ensemble is not available nor are its probability density functions. Moreover a deterministic solution may present the best solution for a given data set, whereas the stochastic approach yields an "average" solution for all the waveforms in the ensemble. Hence, the stochastic solution may not be the desired solution for the given data set. However, when accurate statistics are available, a better solution may be obtained using probabilistic methods. View full abstract»

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  • 2001 Best Chapter Award

    Publication Year: 2002 , Page(s): 54
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    Freely Available from IEEE
  • Spotlight 2 (East Ukraine) - 2000 IEEE microwave pioneer award

    Publication Year: 2002 , Page(s): 58
    Save to Project icon | Request Permissions | PDF file iconPDF (117 KB)  
    Freely Available from IEEE
  • Fast and efficient algorithms in computational electromag nefics [Book Review]

    Publication Year: 2002 , Page(s): 68 - 69
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    Freely Available from IEEE
  • In memoriam: Yuen-Tze Lo

    Publication Year: 2002 , Page(s): 82 - 83
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    Freely Available from IEEE
  • In memoriam: Geoffrey Hyde

    Publication Year: 2002 , Page(s): 83
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    Freely Available from IEEE
  • Baking a ham

    Publication Year: 2002 , Page(s): 84 - 85
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (206 KB) |  | HTML iconHTML  

    First Page of the Article
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  • IEEE-USA Remains Opposed To UCITA

    Publication Year: 2002 , Page(s): 87
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    First Page of the Article
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  • Array theory via a Fourier-transform operational calculus

    Publication Year: 2002 , Page(s): 98 - 102
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (283 KB)  

    The article presents a point of view for array-antenna analysis based on an operational calculus with two-dimensional Fourier transforms. The purpose is to describe the operational calculus, and to employ it in computing the array factor of a finite-extent phased array. Fourier-transform calculus is a very familiar subject to undergraduate electrical engineering students because of its central role in signal analysis, filter analysis and design, and in digital signal processing. The engineering control of the pattern through the parameters of the antenna configuration are particularly clear when the pattern is developed through a two-dimensional Fourier transform operational calculus. View full abstract»

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  • Avoiding interference in planar arrays through the use of artificial neural networks

    Publication Year: 2002 , Page(s): 61 - 65
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (438 KB)  

    This article implements an artificial neural network to find, through computer simulation, the excitations of a square planar array. The array is composed of 52 uniformly spaced subarrays, and has a quasi- in its radiation diagram. This simulation model includes the reduction of any signal interference in the shaped radiating zone after its position has been determined. View full abstract»

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  • An approach for automatic grid generation in three-dimensional FDTD simulations of complex geometries

    Publication Year: 2002 , Page(s): 75 - 80
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (650 KB)  

    The finite-different time-domain (FDTD) method has become a popular method in computational electromagnetics because of its simplicity, flexibility, and efficiency. However, the process of generating a three-dimensional (3D) FDTD grid can be time-consuming and error-prone when manually manipulating complex geometries. In order to expedite the generation of FDTD grids, computer-graphics-based methods can alternatively be used. Starting from the geometric description of the problem domain given by a CAD file, an FDTD grid with a specific spatial resolution can be automatically produced. A simple algorithm to this end is discussed, along with sample results. View full abstract»

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  • Airborne operation of portable electronic devices

    Publication Year: 2002 , Page(s): 30 - 39
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (815 KB) |  | HTML iconHTML  

    Rapidly improving electronic technology has led to a worldwide proliferation of portable electronic devices (PEDs). These have received a portion of the blame (or suspicion) for unexplained aircraft electronic-system anomalies. A significant concern about PED interference with airplane electronic systems, as well as ground communication networks, has brought about many debates; many people question the rationale and the existence of a solid scientific basis for current regulations and policies. The purpose of this paper is to provide a broad view of the issues associated with airborne operation of PEDs. View full abstract»

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  • Electromagnetics for the heart

    Publication Year: 2002 , Page(s): 103 - 105
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (348 KB) |  | HTML iconHTML  

    Previously, the treatment of patients with cardiac arrhythmias was mostly palliative, involving lifelong dependence on medication. Moreover, in a significant portion (10% to 15%) of these patients, available drug therapy has been found unsatisfactory because of a lack of meaningful response or unacceptable, side effects. Surgical intervention has been the principal method of treatment in these cases. However, alternatives to surgery have been sought, in an effort to reduce the cost and morbidity of surgical treatment. During the past decade, minimally invasive microwave and radio-frequency (RF) cardiac ablation - in particular, RF cardiac ablation - has become a widely used procedure for the treatment of cardiac arrhythmias. Minimally invasive intervention offers many benefits: long incisions are replaced with a puncture wound; major cardiac and pulmonary complications are sidestepped; the need for postoperative intensive care is significantly reduced; and, in many cases, minimally invasive intervention offers a "cure" without major surgery. Furthermore, it has important advantages over drugs that are merely palliative, and only alleviate symptoms. Namely, it avoids the side effects and inconvenience of chronic drug therapy. View full abstract»

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  • A method and a GUI for the creation of azimuth-track level-pointing-error corrections

    Publication Year: 2002 , Page(s): 23 - 29
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (518 KB) |  | HTML iconHTML  

    The JPL beam-waveguide (BWG) antennas are used for spacecraft tracking and for radio-astronomy observations. They are mounted on wheels that rotate around an uneven azimuth track, causing antenna deformations, and reducing pointing accuracy. The pointing errors affected by the track irregularities are repeatable, and can therefore be calibrated. The effects of the irregularities of the track can continually be corrected by using a lookup table, created by the interface presented. This paper is a continuation of previous work of Gawronski, Baher and Quintero (see ibid., vol.42, no.2, p.28-38, 2000). It describes the processing the inclinometer data, which includes the verification of repeatability, smoothing, slow-trend removal, re-sampling, and adjustment to a standard format. it also presents a user-friendly interface that process field data and creates a lookup table for pointing-error correction by clicking appropriate buttons on a computer screen. The GUI was tested with the JPL BWG antennas, and may be used with any antennas utilizing an azimuth track. View full abstract»

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  • Deterministic RF ing in phased arrays for the next generation of radio telescopes

    Publication Year: 2002 , Page(s): 13 - 22
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (802 KB) |  | HTML iconHTML  

    A requirement of the next generation of radio telescopes for astronomy is the ability to cope with the forever increasing problem of radio-frequency interference (RFI). Unlike conventional fixed parabolic receivers, currently used in astronomy, the application of phased-array beamforming techniques opens up the possibility to spatially RFI in the RF domain, prior to signal digitization. This paper presents results from the second phased-array experimental demonstrator, the One Square Meter Array, on calibration and RF ing performance. The approach is to deterministically known RFI in the RF beamforming domain, and to adaptively remove the remaining RFI in the digital beamforming domain. A novel array-calibration technique, called the multi-element phase toggle technique (MEP), is presented. This technique allows a fast and very accurate calibration of wide-band phased-array antennas. Array calibration is shown to determine the extent to which RFI can be removed by experimental verification of simulated depths. View full abstract»

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  • Smart-antenna system for mobile communication networks .Part 2. Beamforming and network throughput

    Publication Year: 2002 , Page(s): 106 - 114
    Cited by:  Papers (38)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (711 KB)  

    Part 1 of this paper provided an overview of smart-antenna systems, and presented a planar array as a design example. In addition, Part 1 discussed the potential of smart antennas with regard to providing increased capacity in wireless communication networks. Part 2 introduces the signal-processing aspects of the antenna array. In particular, it describes the utility of direction-of-arrival algorithms in array-antenna systems, and gives an overview of the signal-processing algorithms that are used to adapt the antenna radiation pattern. The adaptive-algorithm descriptions are accompanied by simulation results obtained for a specific network topology. In particular, the antenna system is simulated assuming a mobile network topology that is continuously changing. Basic results presented are the dependence of the overall network throughput on the design of the adaptive-antenna system, and on the properties of the adaptive-beamforming algorithms and associated antenna patterns. View full abstract»

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The IEEE Antennas and Propagation Magazine covers all areas relating to antenna theory, design, and practice.

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Mahta Moghaddam