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Antennas and Propagation Magazine, IEEE

Issue 6 • Date Dec. 2007

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Displaying Results 1 - 25 of 65
  • Front cover - IEEE Antennas and Propagation Magazine

    Page(s): c1
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  • Table of contents Feature Articles

    Page(s): 3
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  • Information for contributors

    Page(s): 4
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  • Magazine staff

    Page(s): 5 - 6
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  • AP-S Officers and Administrative Committee

    Page(s): 7
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  • Editor's Comments

    Page(s): 8 - 225
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  • President's Message

    Page(s): 8 - 10
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  • IEEE International Symposium on Antennas and Propagation and USNC/URSI National Radio Science Meeting - Call for Papers

    Page(s): 11 - 12
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  • Stacked Microstrip-Patch Arrays as Alternative Feeds for Spaceborne Reflector Antennas

    Page(s): 13 - 23
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (7248 KB) |  | HTML iconHTML  

    The feasibility of using stacked microstrip-patch arrays as feeds for offset reflector antennas is investigated in this paper. It is shown that patch arrays can be used as alternatives to the conventionally used horn feeds, which tend to be bulky. In particular, patch arrays can be of interest for spacecraft applications where reduced size and light-weight feeds are highly desirable. In this paper, patch arrays were tailored to provide radiation characteristics similar to those of horn feeds by varying the element spacing and excitation. A reduction in weight was mainly realized by the planar construction of the patch arrays. A full-wave analysis of the feed array, using finite-difference time-domain (FDTD) and PO-based UCLA reflector-analysis codes, was used to test the results of the proposed feed, operating at 1.413 GHz for radiometer applications, and 1.26 GHz for radar applications. A dual-polarized and dual-frequency stacked microstrip-patch element was fabricated and tested. It was then demonstrated that a seven-element hexagonal array design seemed to be the best match to the horn feeds for a 12 m offset-reflector antenna. View full abstract»

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  • Short-Range Ultra-Broadband Terahertz Communications: Concepts and Perspectives

    Page(s): 24 - 39
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (11317 KB) |  | HTML iconHTML  

    We propose the concept of ultra-broadband terahertz communication, based on directed non-line-of-sight (NLOS) transmissions. Potential applications of such a system supporting multi-gigabit data rates are given, and put into the context of currently emerging WLANs/WPANs. The technology and propagation constraints serve as boundary conditions for the determination of the required antenna gain to support ultra-broadband communication. Resulting high-gain antenna requirements will necessitate highly directed transmissions. We propose the use of omni-directional dielectric mirrors to support directed NLOS paths. Their performance is investigated with ray-tracing simulations of a terahertz propagation channel in a dynamic office environment, which is calibrated with measured building-material and mirror parameters. We demonstrate that a directed NLOS path scheme will make a terahertz communication system robust to shadowing. Furthermore, we show that dielectric mirrors covering only parts of the walls will significantly enhance the signal coverage in a typical indoor scenario. View full abstract»

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  • Servo-Performance Parameters of the NASA Deep Space Network Antennas

    Page(s): 40 - 46
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3794 KB) |  | HTML iconHTML  

    The performance of an antenna control system is evaluated using performance parameters such as settling time, bandwidth, steady-state error in rate offsets, and antenna root-mean-square servo error while tracking in wind gusts. The performance parameters are measured in the field, or obtained through analysis and simulations. Limited access time to antennas, incomplete test equipment, limited test/analysis time, and partial models do not allow determination of all the parameters. However, field practice and analytical results indicate correlations among them; hence, even incomplete knowledge of the performance parameters would allow for estimation of the missing parameters. This paper investigates the relationships of the antenna performance parameters as a function of controller gains. It also establishes the interrelationships among the parameters. It does this for an idealized (or rigid) antenna, and extends the relationships to the NASA Deep Space Network antennas (flexible structures with dish sizes of 34 or 70 meters). The results obtained should simplify antenna testing, and allow for better performance evaluation from limited data. View full abstract»

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  • Derivation of the Norton Surface Wave Using the Compensation Theorem

    Page(s): 47 - 57
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (5923 KB) |  | HTML iconHTML  

    This paper presents a tutorial exposition of the derivation of the Norton surface wave using the compensation theorem. Only the case of a vertical electric dipole above an infinite ground plane satisfying an impedance boundary condition is treated. This is the most interesting case in practice, and the one on which applications such as MF AM broadcasting and HF surface-wave radar rely. It is attractive to use the compensation theorem to treat this relatively complex problem. This theorem, itself simply derived starting from Lorentz reciprocity, is easily understood, and the development that follows draws only on ideas already familiar in at least some context to almost all electrical engineers. This makes it for the most part easier to follow than equivalent alternative presentations. While not the first such derivation to have appeared in the literature, and to some extent paralleling these earlier developments to allow direct comparison, the present paper aims to differentiate itself both by being easier to follow and in removing some errors. View full abstract»

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  • Accurate Evaluation of Magnetic- and Electric-Field Losses in Ground Systems

    Page(s): 58 - 70
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (7585 KB) |  | HTML iconHTML  

    The efficiency of ground-based antennas is highly determined by the power dissipated in the ground plane, which can be separated into H-field and E-field losses. In this paper, a new approach is presented for the separation of ground losses that is based on Joule's law. It is theoretically valid at any frequency. Nevertheless, some simplifications can be applied in the low-and medium-frequency bands, where the Earth's soil behaves like a good conductor. In the analysis, the antenna's ground plane has been divided into two zones: a) the artificial ground plane, where a radial-wire ground screen was used; and b) the natural ground plane or bare soil, up to a circular boundary a half wavelength from the antenna's base. In order to avoid overestimating the penetration of fields in the artificial ground plane, the previous theory has been extended by introducing the concept of effective skin depth. The monopole's nonzero equivalent radius effect has been taken into account by means of a modified current distribution. Also, the case of short top-loaded antennas has been treated. H-field and E-field losses have been analyzed by means of equivalent resistances and computed numerically as functions of frequency in the LF and MF bands for different antenna dimensions, ground screens, and soil physical conditions. Some results have also been obtained by Moment-Method simulations. View full abstract»

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  • Power Aspects of the Equivalent Circuit of an Antenna

    Page(s): 71 - 78
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3628 KB) |  | HTML iconHTML  

    The Norton equivalent circuit of a receiving antenna consists of a current generator feeding two admittances in parallel, Ya and YL. Admittance YL represents the load, and the power dissipated in YL, evaluated by "circuit" methods, correctly represents the actual electromagnetic power delivered to the load. The symbol Ya represents the input admittance of the antenna radiating in its transmitting mode. Whether the power dissipated in Ya, again evaluated by circuit methods, is equal to the power scattered by the antenna has been a matter of controversy for quite a few years. The present note seeks to review that recurring problem. View full abstract»

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  • XXIX General Assembly of the International Union of Radio Science, Union Radio Scientifique Internationale (URSI), Call for Papers

    Page(s): 79
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  • 2008 IEEE ANTENNAS AND PROPAGATION SOCIETY MEMBERSHIP APPLICATION

    Page(s): 80
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  • Chapter News

    Page(s): 81 - 85
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  • AP-S Distinguished Lecturer Program for 2006-2007 and Distinguished Lecturers and Their Lectures

    Page(s): 86
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  • Keller's Cone Encountered at a Hotel

    Page(s): 88 - 89
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    The author presents his own personal encounter with Keller's cone. View full abstract»

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  • - Announcement - 2008 Raj Mittra Travel Grants

    Page(s): 90
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  • The European School of Antennas: Structure, Results and Perspectives

    Page(s): 92 - 98
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    The European School of Antennas (ESoA) is a geographically distributed nonprofit post-graduate school on antennas, propagation, and relevant applications. The ESoA courses are distributed in the most accredited European research centers of antennas and wireless systems. In the first three year of life, the ESoA courses involved about 680 students and more than 150 different teachers, mostly university professors. This paper presents the structure of the school, the results obtained since its founding, and its future development and perspectives. View full abstract»

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  • Announcement and Call for Papers ISAPE2008

    Page(s): 100
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  • Design of Modulated End-Fire Antennas

    Page(s): 101 - 110
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    The design presented in this article is dedicated to end-fire antennas with a modulated surface-wave structure fed by a dipole or crossed dipole. For short, these are herein called modulated end-fire antennas. The studies were carried out with a modulated corrugated-rod (disks attached to a metal rod) surface-wave structure. The results obtained may be applied to other types of surface-wave structures, such as dielectric on a metal rod or dipole. The length of the investigated antennas ranged between 1.5lambda and 4.5lambda . The increase in directivity obtained was between 5 dB and 3.5 dB, compared to ordinary non-modulated end-fire antennas with the same lengths. View full abstract»

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  • ANTEM/URSI 2008, Call for Papers

    Page(s): 112
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  • Characterization of Real-World Steered-Beam Antennas from Amplitude-Only Near-Field Data

    Page(s): 113 - 122
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    Phase-less near-field techniques are becoming increasingly more important for antenna characterization, due to the growing interest in millimeter-and sub-millimeter-wave applications, where the near-field phase is difficult or even impossible to measure. In this framework, the routine application of phase-less near-field/far-field (NFFF) transformations to real-world operational antennas is a challenging problem, recently questioned in the literature, requiring algorithms capable of providing reliable and accurate results over a large class of radiators. In the present paper, the possibility of applying phase-less near-field techniques for routine testing of antennas is discussed. We point out how -following the recent developments in the field, and by a formulation of the problem based on proper representations of unknowns and data - it is possible to gain the reliability and the accuracy required for this. Experimental tests were carried out on steered-beam antennas, which have lately been pointed out as "difficult" workbenches, to test the feasibility of operational phase-less near-field/far-field transformations. The experimental results refer to a reflectarray radiating a tilted beam, and to a phased array of large electrical dimensions, radiating a scanned beam and actually employed in real-world applications. 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
W. Ross Stone