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Antennas and Propagation Magazine, IEEE

Issue 1 • Date Feb. 1995

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Displaying Results 1 - 8 of 8
  • Using the matrix pencil method to estimate the parameters of a sum of complex exponentials

    Page(s): 48 - 55
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (676 KB)  

    The approximation of a function by a sum of complex exponentials is a problem that is at least two centuries old. Fundamentally, all techniques discussed in this article proceed from using the same sequence of data samples and vary only, but importantly, in how those samples are used in achieving the parameter estimation. All of these techniques, in other words, seek the same quantitative parameters to represent the sampled data, but use different routes to get there. The techniques for estimating the parameters are either linear or nonlinear. The linear techniques are emphasized in this presentation. In particular, the matrix pencil method is described, which is more robust to noise in the sampled data. The matrix pencil approach has a lower variance of the estimates of the parameters of interest than a polynomial-type method (Prony's method belongs to this category), and is also computationally more efficient. A bandpass version of the matrix pencil can be implemented in hardware, utilizing an AT&T DSP32C chip operating in real time. A copy of the computer program implementing the matrix pencil technique is given in the appendix.<> View full abstract»

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  • Review of domain-decomposition methods for the implementation of FEM on massively parallel computers

    Page(s): 93 - 98
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    The finite-element solution of electromagnetic phenomena, involving electrically large and complex structures, is a major challenge, since both accuracy and efficiency are hard to obtain. The authors introduce the different methods for performing the domain decomposition for distributed memory, multiple-instruction multiple-data (MIMD) multiprocessors. In discussing the advantages and disadvantages of the different methods, we assume that an iterative-matrix method, such as the conjugate gradient method, is used to solve the matrix equation View full abstract»

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  • Site shielding of earth-station antennas

    Page(s): 7 - 24
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    This paper concerns interference in satellite earth stations, due to microwave links sharing the same frequency band, and its solution by site shielding. The uniform theory of diffraction (UTD) has been used to analyze the near field of a parabolic-reflector antenna. An extension of the UTD, in which the influence of the surface impedance is taken into account, has been applied, to calculate the diffraction from the top of the barrier. The theoretical model has been verified in a field-measurement exercise, using a three-meter earth-station antenna, located behind an existing free-standing concrete wall, with a simulated source of interference. The undesirable effects of the barrier on the gain, noise temperature, and the radiation pattern have been studied, and criteria for the clearance of the main beam have been established. Methods of improving shielding effectiveness using absorbing materials and, also, specially shaped diffracting edges have been studied, as well. Laboratory measurements of the diffraction loss of absorbers have been made, and relative advantages are presented. Design guidelines have also been given View full abstract»

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  • Modeling and design of electromagnetically coupled microstrip-patch antennas and antenna arrays

    Page(s): 31 - 39
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    This work is an effort to investigate and derive a simple equivalent-circuit model to represent an electromagnetically coupled microstrip-patch antenna. A simplified theory is developed, based on the broadside-coupled lines and improved-transmission-line methods, to provide for the practical design of such antennas without involving complicated, time-consuming, difficult numerical methods. A number of sample patches are designed, made, and tested to verify the theory. These patches are also incorporated into an array, to evaluate their performance in an array environment View full abstract»

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  • Microstrip-antenna work at NTH/SINTEF DELAB

    Page(s): 25 - 30
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    This paper gives an overview of the microstrip-antenna work at NTH (Norwegian Institute of Technology) and SINTEF DELAB, in Norway. After a description of the organizations, a brief overview of the early developments in the antenna field at NTH and SINTEF is given. The antenna-measurement facilities and CAD tools available are then described, followed by an overview of the main research activities in the field of microstrip antennas View full abstract»

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  • Effect of fabrication imperfections for ground-plane-backed dielectric-resonator antennas

    Page(s): 40 - 47
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    Results of numerical and experimental studies, pertaining to the effect of imperfections such as surface roughness, which could lead to poor mechanical contact between a dielectric resonator and the conducting surfaces on which it resides, are presented. This work simulates the poor-contact effect by introducing air gaps between the dielectric resonator (DR) and the adjacent conducting surfaces. Results are presented which illustrate the effect of air gaps upon the input impedance and resonant frequency of cylindrical-DR antennas, operating in the TM01 and HEM11 modes. Also presented are preliminary results pertaining to the validity of the thin-wire-theory approximation that is used in numerical electromagnetic design codes, to model the coaxial-feed probes, and results pertaining to the effect of an infinite-ground-plane assumption View full abstract»

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  • PCs for AP and other EM reflections

    Page(s): 87 - 90
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    A FORTRAN subroutine is presented, which accurately determines the effective width of a waveguide and its length, by measuring the resonance frequencies of the cavity made of the same waveguide. This measurement method only necessitates a scalar network analyzer and standard waveguide components View full abstract»

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  • A Luneberg-lens update

    Page(s): 76 - 79
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    Some proposed satellite-based mobile communication systems require multibeam systems at millimeter-wave frequencies. This is a primary factor in the renewed interest in Luneberg lenses. Luneberg (1944) lenses prove useful in a variety of antenna and scattering applications. In antenna applications, their chief advantages are an ability to form multiple beams that may point in arbitrary directions, and their broadband behavior. Lens weight, and complexities involved in manufacturing such lenses, remain their primary drawbacks. Unfortunately, no significant advances in the fabrication techniques have come to pass in forty years. However, operation at millimeter-wave frequencies makes the lens weight inconsequential. The vast majority of the research on spherical lenses took place before computers were commonplace in antenna design. The author reviews some of the applications of Luneberg lenses, and adds some more recent data, generated using a numerical model View full abstract»

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W. Ross Stone