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Antennas and Propagation Magazine, IEEE

Issue 3 • Date June 2008

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Displaying Results 1 - 25 of 61
  • Front cover - IEEE Antennas and Propagation Magazine

    Publication Year: 2008 , Page(s): 1
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  • Table of contents

    Publication Year: 2008 , Page(s): 3
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  • Information for contributors

    Publication Year: 2008 , Page(s): 4
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  • Magazine Staff

    Publication Year: 2008 , Page(s): 5 - 6
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  • AP-S Officers and Administrative Committee

    Publication Year: 2008 , Page(s): 7
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  • Editor's comments

    Publication Year: 2008 , Page(s): 8 - 233
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  • President's Message

    Publication Year: 2008 , Page(s): 8 - 9
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  • 2008 AP-S Memebership Form

    Publication Year: 2008 , Page(s): 10
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  • New Insight into the Classical Macdonald Physical Optics Approximation

    Publication Year: 2008 , Page(s): 11 - 20
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (5678 KB) |  | HTML iconHTML  

    The physical optics approximation is widely used in analysis of antennas and scattering problems for electromagnetic and acoustic waves. The present paper investigates the nature of this classical approximation. It is shown that the scattered field in this approximation can be separated into two parts: the reflected field, containing all reflected rays and beams, and the shadow radiation, responsible for the Fresnel diffraction and the forward scattering. This observation elucidates the physics behind the fundamental diffraction law related to the total power scattered by large reflecting objects. It also clarifies the diffraction limit for reduction of scattering by absorbing materials. View full abstract»

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  • Getting the Magazine by Air Freight, Changes of Address or Delivery Problems

    Publication Year: 2008 , Page(s): 20
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  • A Look at the Concept of Channel Capacity from a Maxwellian Viewpoint

    Publication Year: 2008 , Page(s): 21 - 50
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (24590 KB) |  | HTML iconHTML  

    Wireless communication is an active area of current research in communication technology. To assess the performance of a wireless system, one needs to quantify its ability to handle information. Typically, the performance of such systems is characterized in terms of the channel capacity. In this article, we look at the various mathematical representations of the channel capacity, and trace how they have evolved from the initial concept of entropy. Two popular mathematical representations of channel capacity involve the power and the voltage related to the incident field at the receiver. If one uses similar values for the background noise power in the two formalisms, and ensures that the transmitting and receiving antennas are matched, then the two formulas may yield similar results, even though they are functionally different. The essential point to be made here is that the channel capacity, like entropy, is an abstract mathematical number that has little connection to the electromagnetic properties of the system. However, introducing Maxwellian physics can help one interpret the channel-capacity formulas in a physically realistic way by using the vector electromagnetic equations. In electromagnetics, power is carried by the fields, and that is why the fields are fundamental in nature. In this case, a Maxwellian approach to wireless technology is not only relevant, but also vitally important. Such a formalism will correct the variety of deficiencies in the current wireless-communication literature. The primary objective of this paper is to apply the various formulas for channel capacity in a physically proper way. First, the channel capacity of any system needs to be characterized under the same input-power constraints, while simultaneously accounting for the radiation efficiency of the transmitting and receiving antennas. Second, the voltage form of the channel capacity is more useful for wireless systems than the power form, since the sensitivities of the receive- s are generally characterized in terms of the received electric fields. In addition, the received power is at least two orders of magnitude larger than the background noise. Third, in a near-field scenario, it is not clear how to evaluate the power in a simple way. Consequently, we will show that the voltage form of the channel capacity, which depends only on the electric field, is always applicable to both the near and far fields. In contrast, the power form depends on the electric and magnetic fields (unless the antennas are conjugately matched). The solution of the vector electromagnetic problem also illustrates that deploying antennas near the ground yields a higher capacity than placing them on top of a high tower, away from the Earth. In addition, electrical tuning of the antennas further increases the capacity. These subtle points are generally missed by a statistical formulation. In addition, the practice of unrealistically representing antennas by point sources is devoid of any near-field effects, which require both the electric and the magnetic fields to compute the power. Examples are presented for single-input-single-output situations to illustrate the subtleties of the vector nature of the problem, which is missing in current formulations. In particular, the results of simulations of a dielectric box surrounding a receiving antenna suggest that the box enhances signals in some cases, instead of impeding line-of-sight propagation. View full abstract»

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  • Memeber of the Research Staff

    Publication Year: 2008 , Page(s): 50
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  • Cellular-Phone and Hearing-Aid Interaction: An Antenna Solution

    Publication Year: 2008 , Page(s): 51 - 65
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (9145 KB) |  | HTML iconHTML  

    With the introduction of digital cellular phones, hearing-aid users have experienced a severe buzzing noise caused by the interaction between digital cellular phones and hearing aids. The cellular-phone industry, the hearing-aid industry, and consumers have been seeking a solution for the interference issue. Efforts reported in the literature have focused on measurements, modeling, and evaluation of interference and RF emission, but not on methods to solve the problem. In this paper, we focus on the causes of the interference and an understanding of the problem. We also present a method to reduce near-field electromagnetic energy around a cellular phone, mitigating the interference between cellular phones and hearing aids. The theoretical investigation of both the radiation mechanisms and fundamental limits on antennas suggested that a low-g antenna, such as an ultra-wideband antenna, could reduce the near-field intensity. Simulations and measurements were performed at 900 and 1880 MHz, using both low- and high-Q test antennas mounted on a mock cellular phone. The results showed that the peak electric and magnetic near-field strengths of the low-g test antenna were lower than those of a high-Q test antenna by at least 5 dBV/m and 4 dBA/m, respectively. The improvement in the near-field performance for the low-g antenna was without any sacrifice in far-field performance. Furthermore, in the presence of a human head, the simulation results showed that the radiation efficiency of the low-Q test antenna was better than that of the high-Q test antenna. View full abstract»

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  • Radiation Efficiency of Nano-Radius Dipole Antennas in the Microwave and Far-infrared Regimes

    Publication Year: 2008 , Page(s): 66 - 77
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (7764 KB) |  | HTML iconHTML  

    At microwave and far-infrared frequencies, the radiation efficiency of a wire antenna with a radius value smaller than a few hundred nanometers is very low, due to large wire impedances and associated high ohmic losses. However, with the continued miniaturization of electronic devices, nano-radius interconnects and antennas are desirable. In this work, the relationships among wire radius, conductivity, frequency, and ohmic loss are examined for dipole antennas. Simple formulas are derived for the distributed resistance, effective conductivity, and radius required to achieve a desired radiation efficiency, and particular emphasis is given to half-wavelength antennas. Several methods to improve antenna efficiency at sub-100-nm radius values are discussed, including the use of superconducting nanowires and multi-wall carbon nanotubes. View full abstract»

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  • Radiation of High-Gain Cavity-Backed Slot Antennas Through a Two-Layer Superstrate

    Publication Year: 2008 , Page(s): 78 - 87
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (6057 KB) |  | HTML iconHTML  

    The radiation of cavity-backed slot (CBS) antennas through a two-layer superstrate is studied in this paper. A novel transmission-line model is proposed to explain the gain-enhancement effect of the superstrate on cavity-backed slot antennas. Experimental result showed that a single cavity-backed slot antenna can achieve a high gain of 16.7 dBi through a properly designed superstrate, and this gain-enhancement property is valid for array configurations, as well. A rotationally arranged four-slot array, covered by the superstrate, is also investigated, to demonstrate that good circular polarization and high gain can be obtained from the superstrate-covered slot antennas. View full abstract»

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  • Electrically Small Spheroidal Loops Wound on Hollow Ferrite Cores

    Publication Year: 2008 , Page(s): 88 - 94
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (3923 KB) |  | HTML iconHTML  

    The complete electrical properties of a small loop wound on a hollow spheroidal ferrite core are calculated using quasistatic theory. Closed-form expressions are derived for all of the elements of an equivalent circuit. It is shown that not only may the bandwidth be increased by the use of a ferrite core, but also that by redistributing the same volume of ferrite over a slightly larger spheroid as a thin layer, the bandwidth may be increased even more. Core losses are computed for a typical ferrite. Although the primary objective is to simplify the design of a transmitting antenna for use in the lower part of the HF band, 2 to 8 MHz, the theory presented is equally valid for the design of receiving antennas and for other frequencies. View full abstract»

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  • Call for Papers

    Publication Year: 2008 , Page(s): 96 - 97
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  • Chapter News

    Publication Year: 2008 , Page(s): 98 - 99
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  • AP-S Distinguished Lecturer Program for 2007-2009

    Publication Year: 2008 , Page(s): 100
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  • National Radio Science Meeting

    Publication Year: 2008 , Page(s): 102 - 103
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  • Design Formula for Sierpinski Gasket Pre-Fractal Planar-Monopole Antennas [Antenna Designer's Notebook]

    Publication Year: 2008 , Page(s): 104 - 107
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (2443 KB)  

    An improved formula for determination of resonant frequencies in different Sierpinski modes is developed from other existing formulas, using physical and analytical reasoning. The superiority of the proposed formula over other existing formulas is verified by comparing the results with those from experiments and simulations. A design formula for the side length of the generating Sierpinski triangle is also proposed by algebraic rearrangement of the formula for the resonant frequency. View full abstract»

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  • A Low-Power High-Sensitivity X-Band Rail SAR Imaging System [Measurement's Corner]

    Publication Year: 2008 , Page(s): 108 - 115
    Cited by:  Papers (5)
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    Wideband radar imaging with range gating and high sensitivity can be achieved with the use of low-cost commercially available narrowband IF filters. Such filters reduce the effective receiver noise bandwidth of the radar system. This allows for high sensitivity, comparable to that of single-sideband radio receivers, while at the same time acquiring de-chirped wide-band received waveforms. A carefully developed radar architecture, based on the use of these IF filters, is shown in this paper. This radar architecture is then implemented in an X-band linear rail synthetic-aperture-radar (SAR) imaging system. The X- band rail SAR is a linear FM-chirped radar, which chirps from approximately 7.5 GHz to 12.5 GHz. The radar front end is mounted onto an eight-foot-long linear rail. The transmitted power is adjustable to 10dBm or less. It will be shown that objects as small as groups of pushpins in free space can be imaged using transmitted power as low as 10 nW. These results are compared to previous direct-conversion X-band FMCW rail SAR work. A high-sensitivity X-band rail SAR such as this could be useful for measuring low-radar-cross-section (RCS) targets. This radar could be used in high clutter environments that require a range gate. This low-power X-band rail SAR could be useful for operation in restricted transmission areas, where maximum radiated power is severely limited. Other applications include any that require low transmitter power, such as automotive radar. View full abstract»

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  • Waveform Diversity & Design Conference

    Publication Year: 2008 , Page(s): 118
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  • Reviews and Abstracts [review of Antenna Engineering Handbook (Volakis, J.L., Ed.; 2007)]

    Publication Year: 2008 , Page(s): 119 - 126
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  • First Call For Papers

    Publication Year: 2008 , Page(s): 128
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Aims & Scope

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

Full Aims & Scope

Meet Our Editors

Editor-in-Chief
Mahta Moghaddam