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Antennas and Propagation Magazine, IEEE

Issue 4 • Date Aug. 2005

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Displaying Results 1 - 25 of 74
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  • Roses are red, violets are blue... [sky colour]

    Page(s): 128 - 129
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (78 KB)  

    The author considers why the sky appears blue. Features of Rayleigh scattering are mentioned as are features of the human visual system. A demonstration for classroom use is also mentioned briefly. View full abstract»

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  • Control systems of the large millimeter telescope

    Page(s): 41 - 49
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (442 KB) |  | HTML iconHTML  

    This paper presents the analysis results (in terms of settling time, bandwidth, and servo error in wind disturbances) of four control systems designed for the Large Millimeter Telescope (LMT). The first system, called PP, consists of the proportional and integral (PI) controllers in the rate and position loops, and is widely used in the antenna and radio telescope industry. The analysis shows that the PP control system's performance is remarkably good when compared to similar control systems applied to typical antennas. This performance is achieved because the LMT structure is exceptionally rigid; however, it does not meet the stringent LMT pointing requirements. The second system, called PL, consists of the PI controller in the rate loop, and the linear-quadratic-Gaussian (LQG) controller in the position loop. This type of controller is implemented in the NASA Deep Space Network antennas, where pointing accuracy is twice that of the PP control system. The third system, called LP, consists of the LQG controller in the rate loop, and the proportional-integral-derivative (PID) controller in the position loop. This type of loop has not been yet implemented at known antennas or radio telescopes, but the analysis shows that its pointing accuracy is the ten times better than the PP control system. The fourth system, called LL, consists of the LQG controller in both the rate loop and the position loop. It is the best of the four, with accuracy 250 times better than the PP system. It is thus worth further investigation to identify implementation challenges for telescopes with high pointing requirements. View full abstract»

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  • Parallel multilevel fast multipole method for solving large-scale problems

    Page(s): 110 - 118
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (517 KB)  

    The Multilevel Fast Multipole Method (FMM) is a well-established method and can be applied to solve electromagnetic (EM) scattering problems. Compared with other traditional methods, it requires less computational time and memory. However, constrained by a single processor's speed and memory limitations, the problem size that can be solved by serial implementation is still relatively small. For a million-unknown target, the computational time on a single processor is intolerable, and memory could be easily exhausted. Parallel-computing technology, which can utilize multiprocessors, provides an efficient way to solve electrically large-scale EM problems. This paper will focus on discussing the parallel methodologies applied to a multilevel FMM code, as well as demonstrating the computational efficiency of the parallel approach. View full abstract»

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  • In Memoriam: Roberto Tiberio

    Page(s): 180
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    Freely Available from IEEE
  • President's message

    Page(s): 7 - 9
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  • Propagation corner

    Page(s): 130
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  • Multi-objective genetic optimization of Yagi-Uda arrays with additional parasitic elements

    Page(s): 92 - 97
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    The,design of modified Yagi-Uda arrays with additional parasitic elements in the area of the radiating dipole, acting either as reflectors or directors, is presented. The genetic algorithms are employed, and various objective functions concerning gain, front-to-back ratio, and the latter combined with desired input impedance, are examined. Comparisons are made among the modified and conventional Yagi-Uda configurations for different weighting coefficients of the fitness functions. The modified Yagi-Uda array outperforms the conventional Yagi-Uda array, because it achieves higher performance standards over an extended bandwidth around 2.4 GHz. View full abstract»

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  • Chapter news

    Page(s): 84 - 86
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  • Uniform circular arrays for smart antennas

    Page(s): 192 - 206
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    As the growing demand for mobile communications constantly increases, the need for better coverage, improved capacity, and higher transmission quality rises. Thus, a more efficient use of the radio spectrum is required. Small antenna systems are capable of efficiently utilizing the radio spectrum and, thus, hold a promise for an effective solution to the present wireless systems' problems, while also achieving reliable and robust high-speed high-data-rate transmission. Although numerous studies for smart antennas have already been conducted using rectilinear arrays, including mostly uniform linear arrays (ULAs) and uniform rectangular arrays (URAs), not as much effort has been devoted to other configurations. In this paper, the performance of smart antennas with uniform circular arrays (UCAs) is examined. A profound justification for this selection is the symmetry possessed by uniform circular arrays. This property provides uniform circular arrays with a major advantage: the ability to scan a beam azimuthally through 360° with little change in either the beamwidth or the sidelobe level. With the use of uniform circular arrays, the two main issues related to smart antennas - estimation of the direction of arrival from incoming signals and bearnforming - are both examined. View full abstract»

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  • In Memoriam: Kasra Barkeshli

    Page(s): 181
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    Freely Available from IEEE
  • The European School of Antennas: the new model of distributed PhD school of the antenna center of excellence

    Page(s): 120 - 125
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    The European School of Antennas is a new model of a geographically distributed PhD school, which aims to improve the advanced antenna training and research in Europe. The school is organized in the framework of the Antenna Center of Excellence (ACE), a "Network of Excellence" financed by the sixth framework program of the European Union. The school is constituted as a highly qualified integrated set of advanced courses at the PhD level, distributed in the most accredited European research centers on antennas. The general objectives of the school are: i) strengthening the European excellence on antennas; ii) completing the individual PhD curricula of students in electrical and information engineering by offering interaction with the best trainers in Europe; iii) increasing the link between European universities and industries in antenna research and development; and iv) facilitating the interchange of ideas among early-stage researchers and teachers, thus increasing the future mobility and synergy. The school is furnished with centralized Web support, and this is coordinated so that the courses have the same format and apply common basic rules for exams and credits. View full abstract»

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  • A limitation on the small-scale demonstration of retrodirective microwave power transmission from the solar power satellite

    Page(s): 67 - 72
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (387 KB) |  | HTML iconHTML  

    The solar power satellite (SPS) is a future system for transmitting a high-power microwave beam to the Earth using a large, space-based retrodirective array. However, the small-scale demonstration of a prototype retrodirective transmitter for this application faces a basic limitation and associated tradeoffs, which are identified and described in this paper. Computer-simulated examples are presented, and recommendations are made. View full abstract»

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  • The performance properties of electrically small resonant multiple-arm folded wire antennas

    Page(s): 13 - 27
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (878 KB) |  | HTML iconHTML  

    In this tutorial article, the resonant radiation properties of electrically small, multiple-arm, folded wire antennas are considered and compared as a function of the antenna's height, the cylindrical diameter occupied, the geometry, and the number of folded arms within the antenna structure. The radiation properties considered include resonant resistance, efficiency, radiation patterns, and the operating bandwidth, which is characterized using the antenna's quality factor (Q). It is shown that electrically small, multiple-arm, folded wire antenna designs offer significant performance improvements relative to simple open-ended wire antennas, in terms of increased resonant resistance, bandwidth, and efficiency. However, when multiple-arm, folded wire antennas of the same height and cylindrical diameter, but having significantly different geometries, are made to be self-resonant at the same frequency, they exhibit similar resonant performance properties. This illustrates that the resonant performance properties of these antennas are primarily established by their height and the physical volume occupied relative to the resonant wavelength. Various design parameters are considered and described for achieving self-resonance and a reasonable impedance match with an electrically small, multiple-arm folded wire antenna. Finally, the performance properties of the multiple-arm folded wire configurations are compared with those of an impedance-matched, non-folded, open-ended wire configuration. It is shown that the multiple-arm folded wire configurations exhibit a lower Q than the impedance-matched, non-folded wire configuration. View full abstract»

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  • Trepidation-free teamwork teaching

    Page(s): 161 - 163
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (171 KB)  

    Teamwork is a fact of life for engineers, and sooner (hopefully) or later, successful engineers develop a good set of skills for working together to accomplish a project. Somewhat more challenging is working on a team that includes non-engineers: the "marketing department", for instance. Since the advent of ABET 2000, most professors are aware of this challenge, and have found ways to include teamwork in their classes and curriculum. This column provides an introduction to teamwork resources available on the IEEE A-P-S Education Web site. Tools to help students understand team dynamics, to help students organize their teams, and to help assess the team experience are given. This material is adapted from materials prepared by the University of Utah CLEAR Center. The author gratefully acknowledges the contributions of April Kedrowicz, Katie Sullivan, Juliane Mora, Damon Hall, and Andrew Dohanos. View full abstract»

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  • Report on the TELSIKS 2005 Conference

    Page(s): 137 - 139
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  • AMTA Corner

    Page(s): 212 - 213
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  • To cite or not to cite

    Page(s): 182 - 183
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  • Editor's comments

    Page(s): 7 - 225
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  • The "very-near-field" region of equiphase radiating apertures

    Page(s): 50 - 66
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (990 KB) |  | HTML iconHTML  

    The purpose of this article is to investigate the so-called "near-field reactive" or "very-near-field" region of radiating apertures with different shapes and aperture illuminations. In this unusual and rather unknown region, we underline the specific behavior of the radiated fields, the wave impedance, and the power density. Thanks to these properties, we succeed in. determining, in the first part, the outer boundary of the "very-near-field" region of a circular aperture with a uniform illumination law. Then, we review the influence of the illumination law and of the aperture shape on the extent of this region, through the cases of parabolic or cosine laws, and the case of square-shaped aperture. This study can find various applications in the wireless communications and radar antenna domains and, more recently, in electromagnetic compatibility problems. View full abstract»

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  • Predicting the radio channel beyond second-generation wireless systems

    Page(s): 28 - 40
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (807 KB) |  | HTML iconHTML  

    Ray-optical methods incorporating Geometric Optics (GO) and the Uniform Theory of Diffraction (UTD) are appropriate for the representation of radiowave propagation in cities for frequencies in the UHF band and above, where the wavelength is small compared to building dimensions. Various ray codes have been written to implement the ray representation. Because the rays undergo multiple interactions with the buildings over long distances, the codes make various assumptions to reduce running time. This paper reviews the types of assumptions that have been made, the ways in which the ray procedures have been implemented, and the accuracy that can be expected from the predictions. The paper gives examples of how the computed ray quantities have been used to simulate the characteristics of the radio channel (besides received power) that impact the designs of different radio systems. 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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Editor-in-Chief
Mahta Moghaddam