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Antennas and Propagation Magazine, IEEE

Issue 2 • Date April 1996

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Displaying Results 1 - 10 of 10
  • An Introduction to Optimization

    Publication Year: 1996
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | PDF file iconPDF (170 KB)  
    Freely Available from IEEE
  • Electromagnetic Pulse Propogation in Causal Dielectircs

    Publication Year: 1996
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (253 KB)  

    First Page of the Article
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  • Radio sociology [noise investigation]

    Publication Year: 1996 , Page(s): 45 - 47
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    The article discusses the use of radio telemetry in wildlife research. An aircraft was used to locate a migrating, radio-tagged, sharp-shinned hawk. A 222 MHz four-element Yagi receiving antenna was clamped to the entrance step on the right side of the aircraft, so that it pointed in the direction normal to the direction of flight. The idea was to climb to an appropriate altitude, and fly in large circles to scan a substantial area for the missing bird. While the antenna beam swept across a small town a rush of noise-like sound was heard. This resulted in an investigation of the relationship between a town's radiation (radio noise) signature and its other attributes, such as economic type, population, geographic concentration, etc View full abstract»

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  • Spherical-multipole analysis of electromagnetic and acoustical scattering by a semi-infinite elliptic cone

    Publication Year: 1996 , Page(s): 33 - 44
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1176 KB)  

    The spherical-multipole analysis of scalar scattering by an acoustically soft or hard elliptic cone, and of electromagnetic scattering by a perfectly conducting elliptic cone, are presented. The series expansions of the exact solutions are of poor convergence, if both source and field points are far from the cone's tip. A mathematical transformation for the acceleration of convergence-due to Euler-is applied to these expansions, to numerically determine the scattering cross sections of these objects. This powerful method can also be used for the numerical evaluation of diffraction coefficients. The paper contains a review of scientific work concerning scattering by objects with edges, corners, tips, etc View full abstract»

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  • On the PML concept: a view from the outside

    Publication Year: 1996 , Page(s): 48 - 51
    Cited by:  Papers (3)
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    The idea that an absorbing half space can be reflectionless is most intriguing. We present an exposition of the wave theory using impedance concepts. Some limitations are also mentioned. The PML (perfectly matched layer) has received considerable attention lately. The idea is not entirely new, because the concept of “invisible scatterers” was put forth over twenty years ago. The idea then, and to some extent now, is that the absorbing region should be active in some sense. An equivalent approach is to stretch the coordinates so that Maxwell's equations are modified within the absorber. The author favours the active-medium approach, designed in such a manner that Maxwell's equations don't need to be modified. As Sacks et al. (see IEEE Transactions on Antennas and Propagation, AP-43, p.1460, 1995) showed, this is a great convenience in applying the finite-element method to open-region problems View full abstract»

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  • Some European satellite-antenna developments and trends

    Publication Year: 1996 , Page(s): 9 - 21
    Cited by:  Papers (6)  |  Patents (2)
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    The environment, as well as the mass and available power limitations specific to space missions, add special constraints. These lead to the use of exotic low-mass, high-stability materials, with advanced mechanical and thermal designs. Also, antenna front ends must be tailored for optimum efficiency and power handling. Researchers and engineers in universities, research institutes, and industrial laboratories, from the 14 member states of the European Space Agency (ESA), together with staff from the European Space Agency's Technology Centre (ESTEC) antenna section and from project teams, have studied and developed software-modeling tools, critical reflector and array technologies, novel antenna architectures, and special measurement techniques to cope with these requirements. This paper presents an overview of some of the latest antenna-design tools and technology developments, supported by ESA for space applications. The following topics are covered reflectors, feed systems, and direct-radiating arrays. Some trends and developments in space antenna requirements and technologies are outlined View full abstract»

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  • Modeling effective properties of chiral composites

    Publication Year: 1996 , Page(s): 22 - 32
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1280 KB)  

    After a brief overview of the concepts of electromagnetic chirality and wave propagation in chiral media, this paper deals with the field of microwave-chiral-material modeling. First, studies regarding the scattering of single-chiral or non-chiral elements with different shapes (various designs of helices, Ω-shaped scatterers, wires, and loops) are presented. Results of the backscattered field given by different computer codes are compared. Comparisons among analytical, numerical, and experimental results are also reported. Second, the case of a collection of chiral inclusions is treated. A review of different methods, developed to estimate average properties of helix-loaded materials, is given. Modeling of the effective properties of a chiral slab, such as the rotation angle, ellipticity, permittivity, and permeability, is explored. Reflection and transmission coefficients, evaluated by various methods, are compared with each other, and with measurements. Limitations of the models, possible improvements, and new directions for research are also described. Finally, applications of such composites to the design of radar-absorbing materials are addressed View full abstract»

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  • The microwave point of view on software validation

    Publication Year: 1996 , Page(s): 68 - 71
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    Validation generally consists of a “Good Agreement Between Measured And Calculated” (GABMAC) plot. Unfortunately, when one looks at microwaves-related papers, error bars are rarely plotted on measured data, and quantitative estimates of error are typically absent. Further, convergence analyses, if performed, are rarely mentioned, and test structures are not checked for sensitivity to analysis error. Meanwhile, the discussion of these issues in the antenna field is on-going and active. In fact, it has progressed to the point that you are asking for input from other technical areas. The author describes the situation in the microwave field as he sees it View full abstract»

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  • Error estimation for numerical differential equations

    Publication Year: 1996 , Page(s): 71 - 76
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (628 KB)  

    Given a capable human being and a computer, it is possible to make an approximation to the solution of a nonlinear differential equation. However, under the (usually correct) assumption that the equation is analytically intractable, the result of the computation is not the exact solution; indeed it may be so far from the exact solution as to be completely useless. We are interested in the relationship between the effort expended by the human and the computer, and the duality of the computed approximation to a partial or ordinary differential equation. To be specific, we would like to think in terms of a cost-benefit analysis. The cost of the computation is a combination of the human effort and computer resources used to obtain the approximation. The benefit includes, of course, the computed approximation, but it also includes an estimate of the quality of the approximation, that is, an error estimate. It is our opinion that in computational science, as with the experimental sciences, results should always be presented with some estimate of their accuracy. In addition, however, there is another facet to error estimation: one cannot even attempt a cost-benefit analysis or efficiency comparison of methods without an error estimate to evaluate the results View full abstract»

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  • Cross-polarization tolerance requirements of square microstrip patches

    Publication Year: 1996 , Page(s): 56 - 58
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (408 KB)  

    We normally feed a rectangular patch along the centerline of the H-plane (the non-resonant width). This is done to eliminate excitation of the patch in a mode along the other axis. The second mode radiates cross polarization. This article provides the tolerance requirements, given the cross polarization. The rectangular microstrip patch radiates its peak cross polarization in the diagonal planes, even when the antenna is fed perfectly. This cross polarization is low. When we locate the feed along the centerline of the H-plane of the patch, the impedance match to the TM01 mode is poor, and the antenna does not radiate significant power at boresight to the patch. Often we design a square patch, so that we can radiate orthogonal-linear polarizations (or dual-circular polarizations) by using two feeds. If we fail to place the feed probe, aperture, or microstrip line along the H-plane axis, the cross-polarization level rises View full abstract»

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Mahta Moghaddam