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Antennas and Propagation, IEEE Transactions on

Issue 5 • Date May 1995

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Displaying Results 1 - 18 of 18
  • Comments on "The electromagnetic field of a vertical electric dipole over the Earth or sea" [with reply]

    Publication Year: 1995 , Page(s): 541 - 544
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (211 KB)  

    Yokoyama makes some comments on the "numerical distance" contained in the surface wave term in the paper by King and Sandler (see ibid., vol.42, p.383, 1994) comparing it with the one obtained by former authors. He comments on the parameter P in the Fresnel-integral term in the paper. Yokoyama concludes that for the calculation of such a problem in a semi-sphere, the spherical polar coordinate system is preferable to the cylindrical coordinate system including the case of lateral waves. King and Sandler reply to the Comment.<> View full abstract»

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  • Comments on "A design of AM/FM mobile telephone triband antenna" [with reply]

    Publication Year: 1995 , Page(s): 544 - 545
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (78 KB)  

    Ploussios has read the paper by Egashira et al. (see ibid., vol.42, p.538, 1994), in which they describe the design of multiple band antennas using "double sleeves." He claims that the design of multiple band antennas employing multiple coaxial sleeves of the type described in the paper has been done before and is patented by Ploussios. The patent, 4509056, entitled "Multifrequency antenna employing tuned sleeve chokes," describes the use of multiple coaxial chokes in monopole and dipole type elements. The chokes (sleeves) are arranged in series and parallel, resulting in operation over selected frequency bands that are not harmonically related. The patent includes a description of two- and three-band monopole and dipole designs. Egashira et al. reply to the Comment. They conclude that it is their view that the triband antenna of the AM/FM and mobile telephone (with two bands of mobile station band and base one) cannot be designed using the ideas in Dr. Ploussios' patent.<> View full abstract»

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  • A novel delta gap source model for center fed cylindrical dipoles

    Publication Year: 1995 , Page(s): 537 - 540
    Cited by:  Papers (25)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (356 KB)  

    A novel delta gap source model is presented which improves the convergence of the numerical solution of the electric field integral equation (EFIE) using thin wire theory. This delta source model yields a stable solution for the current at the source location, both computed and measured current distributions and input admittances for cylindrical monopole antennas are presented View full abstract»

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  • Equivalence of adaptive array diagonal loading and omnidirectional jamming

    Publication Year: 1995 , Page(s): 540 - 541
    Cited by:  Papers (7)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (200 KB)  

    Diagonal loading, where a diagonal matrix is added to the estimate of the covariance matrix, is often used in adaptive arrays to minimize the array's responsiveness to random fluctuations in the estimate of the interference environment. Poor estimates of the covariance matrix often result in high random sidelobes in the sample matrix inversion (SMI) adapted pattern. It is shown in this communication that an omnidirectional spread of uniform jammers arriving at a linear array of half-wavelength spaced elements with cosine element patterns also produces a diagonal matrix. This equivalence of form is useful in visualizing the effects of diagonal loading and understanding the resulting patterns View full abstract»

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  • A theoretical study of numerical absorbing boundary conditions

    Publication Year: 1995 , Page(s): 478 - 487
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (808 KB)  

    Electromagnetic field computation involving inhomogeneous, arbitrarily-shaped objects may be carried out conveniently by using partial differential equation techniques, e.g., the finite element method (FEM). When solving open region problems using these techniques, it becomes necessary to enclose the scatterer with an outer boundary on which an absorbing boundary condition (ABC) is applied, and analytically-derived ABCs, e.g., the Bayliss-Gunzburger-Turkel and Engquist-Majda boundary conditions have been used extensively for this purpose. Numerical absorbing boundary conditions (NABCs) have been proposed as alternatives to analytical ABCs, and they are based upon a numerically-derived relationship that links the values of the field at the boundary nodes to those at the neighboring nodes. In the paper the authors demonstrate, analytically, that these NABCs become equivalent to many of the existing analytical ABCs in the limit as the cell size tends to zero. In addition, one can evaluate the numerical efficiency of these NABCs by using as an indicator the reflection coefficient for plane and cylindrical waves incident upon an arbitrary boundary View full abstract»

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  • The use of Huygens' equivalence principle for solving 3-D volume integral equation of scattering

    Publication Year: 1995 , Page(s): 500 - 507
    Cited by:  Papers (10)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    A three-dimensional (3-D) version of the nested equivalent principle algorithm (NEPAL) is presented. In 3-D, a scatterer is first decomposed into N subscatterers. Then, spherical wave functions are used to represent the scattered field of the subscatterers. Subscatterers are divided into different levels of groups in a nested manner. For example, each group consists of eight subgroups, and each subgroup contains eight sub-subgroups, and so on. For each subgroup, the scattering solution is first solved and the number of subscatterers of the subgroup is then reduced by replacing the interior subscatterers with boundary subscatterers using Huygens' equivalence principle. As a result, when the subgroups are combined to form a higher level group, the group will have a smaller number of subscatterers. This process is repeated for each level, and in the last level, the number of subscatterers is proportional to that of boundary size of the scatterers. This algorithm has a computational complexity of O(N2) in three dimensions for all excitations and has the advantage of solving large scattering problems for multiple excitations. This is in contrast to Gaussian elimination which has a computational complexity of O(N3) View full abstract»

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  • Bilateral averaging over receiving and transmitting areas for accurate measurements of sector average signal strength inside buildings

    Publication Year: 1995 , Page(s): 508 - 512
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    In defining path loss for narrowband systems, it is common to introduce the concept of the sector or local average in order to remove the rapid (Rayleigh or Rician) fading. As originally developed for cellular mobile radio (CMR) systems, the sector average is obtained from the spatial average of the received signal as the mobile traverses a path of 20 or so wavelengths. This approach has also been applied indoors with the assumption that a unique average could be obtained by moving either end of the radio link. Unlike the CMR path for indoor propagation, however, both ends of the radio link are in a rich multipath environment. It is shown both theoretically and experimentally that moving both ends of the link is required to achieve a unique average. When averaging is accomplished by moving only one end, the result can experience variations of as much as ±2 dB when the other end is moved by a fraction of a wavelength View full abstract»

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  • Asymptotic expressions for the surface currents induced on a cylindrically curved impedance strip

    Publication Year: 1995 , Page(s): 453 - 463
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (680 KB)  

    The present paper is concerned with the derivation of the electric and magnetic surface currents induced on a cylindrical curved impedance strip. By considering the locality of the high-frequency diffraction phenomena the physical (-π,π) interval for the usual cylindrical polar angle is replaced by an abstract infinite interval (-∞,∞) whereby the related mixed boundary value problem is formulated as a “modified matrix Hilbert” problem. By using the Debye approximations for the Hankel and Bessel functions involved, the modified matrix Hilbert problem is first decoupled and then reduced to two pairs of simultaneous Fredholm integral equations of the second kind which are solved by iterations, The explicit expressions for the electric and magnetic surface current components attributable to the reflection, edge or surface diffractions of the incident field as well as to the edge reflections of these components themselves are obtained by evaluating the current integrals asymptotically. The results derived in the paper constitute also a rigorous proof for a conjecture made by Idemen on the reflections of the surface currents at the edges View full abstract»

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  • Optimal receive antenna polarization in the presence of interference and noise

    Publication Year: 1995 , Page(s): 473 - 477
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (324 KB)  

    The receive antenna polarization that maximizes the signal-to-interference-plus-noise power ratio (SINR) for an arbitrarily polarized signal is determined in the presence of arbitrarily polarized interference and thermal noise. The derivation makes use of the Poincare sphere representation of polarization and reduces the optimization problem to solution of a single transcendental equation. SINR performance is given in terms of degradation from the polarization matched, noise only case. Finally, a comparison of this optimum-pol strategy, with pol-nulling the interferer and pol-matching the signal is presented. These results provide insight into applying polarization theory to improve signal reception in the presence of interference and thermal noise View full abstract»

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  • Analysis of the selective behavior of multilayer structures with a dielectric grating

    Publication Year: 1995 , Page(s): 529 - 533
    Cited by:  Papers (4)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (500 KB)  

    The potential use as dichroic surfaces in the millimeter frequency band of multilayer dielectric structures with a grating in one of the layers is examined. It is shown that the selectivity of the structure may be increased by using a convenient array of dielectric sections in the characteristic cell of the periodic layer. It is also shown how the selective behavior of the structure depends on the angle of incidence of the wave that excites the structure and on the height-periodicity ratio of the periodic layer. In addition, for an unloaded periodic layer, an approximate procedure is described to predict how many times and at which frequencies maximum reflection occurs. The effect of loading the periodic layer with increasing number of dielectric layers is examined with the conclusion that the number of frequencies where maximum reflection occurs may be increased View full abstract»

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  • Application of the integral equation-asymptotic phase method to two-dimensional scattering

    Publication Year: 1995 , Page(s): 534 - 537
    Cited by:  Papers (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (396 KB)  

    A hybrid-procedure called the integral equation-asymptotic phase (IE-AP) method is investigated for scattering from perfectly conducting cylinders of arbitrary cross-section shape. The IE-AP approach employs an asymptotic solution to predict the relatively rapid phase dependence of the unknown current distribution, to leave a slowly varying residual function that can be represented by a coarse density of unknowns. In the present investigation, the current density appearing within the combined-field integral equation is replaced by the product of a rapidly varying phase function obtained from the physical optics current and a residual function. The resulting equation is discretized by the method of moments, using subsectional quadratic polynomial basis functions defined on curved cells to represent the residual function. Results show that the required density of unknowns can often be as few as one per wavelength on average without a significant loss of accuracy in the computed current density, even for scatterers with corners View full abstract»

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  • Depolarizing trihedral corner reflectors for radar navigation and remote sensing

    Publication Year: 1995 , Page(s): 513 - 518
    Cited by:  Papers (9)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    A conventional trihedral corner reflector can be modified to present either a twist-polarizing or a circularly polarizing response by adding conducting fins of rectangular corrugations of prescribed dimensions and orientation to one of its interior surfaces. Since the modified reflector retains most of the mechanical ruggedness and ease of manufacture of the original, it is suitable for deployment in the field for extended periods as required in radar navigation and remote sensing applications. For most directions of incidence the response of the reflector is dominated by triple-bounce reflections from the interior and is a function of the size and shape of the reflecting panels, the dimensions of the corrugations, and the orientation of the reflector with respect to the radar. Experimental results show that prototype twist-polarizing and circularly polarizing reflectors respond as predicted View full abstract»

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  • Pulsed beam diffraction by a perfectly conducting wedge: local scattering models

    Publication Year: 1995 , Page(s): 519 - 528
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (848 KB)  

    Develops local scattering models for a collimated wavepacket (pulsed beam, PB) impinging on a perfectly conducting wedge. They are derived from an exact solution that has been derived previously. Unlike the exact solution, the local solutions have explicit space-time forms which parameterize the problem in terms of tractable phenomena that may be extended to noncanonical configurations. This is done in the second half of the paper wherein the local models are extended to accommodate astigmatic wavepackets for which there is no exact solution. The local models developed have the format of the geometrical theory diffraction and of the uniform theory of diffraction (UTD), extended to accommodate PB fields: they are governed by transient diffraction functions (time-domain counterparts of the UTD diffraction coefficient) but also include structure functions that describe the space-time distribution of the scattered wavepacket. They explain, uniformly, the physics of the scattering phenomena as a function of the PB parameters: direction, distance from the edge, spatial collimation, and pulse length View full abstract»

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  • High resolution spherical microwave holography

    Publication Year: 1995 , Page(s): 464 - 472
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (892 KB)  

    A practical technique is developed to determine the electric and/or magnetic field on objects and sources inside a spherical measurement surface. The technique, known as spherical microwave holography (SMH), provides a nondestructive, nonintrusive method of point-by-point evaluation of antennas and radomes over their spatial extent. The resolution capability of SMH is developed and demonstrated by measurements. Resolution in SMH is only limited by the measurement system's capabilities. Dielectric and metallic obstacles on the surface of a radome are located and identified. Resolution as small as 0.33λ0 is demonstrated View full abstract»

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  • The corrected induced surface current for arbitrary conducting objects at resonance frequencies

    Publication Year: 1995 , Page(s): 448 - 452
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    It is well known that using the method of moments in conjunction with either the electric or magnetic field surface integral equations (EFIE or MFIE) produces inaccurate surface currents on conducting bodies at resonance frequencies. A new technique (based on singular value decomposition) is developed to correct the computed current by adding a correction factor term. This term is seen to be the resonant mode current, obtained by employing the power method in the moment method matrix, multiplied by an unknown complex factor. Applying the condition of vanishing field inside the conducting object results in obtaining the unknown complex factor. Therefore, this technique is hereafter referred to as correction factor technique (CFT). When the computed surface current on a conducting sphere, proposed technique, is compared with the exact one, the numerical results show excellent agreement View full abstract»

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  • Backscattering enhancement and clustering effects of randomly distributed dielectric cylinders overlying a dielectric half space based on Monte-Carlo simulations

    Publication Year: 1995 , Page(s): 488 - 499
    Cited by:  Papers (35)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (936 KB)  

    Backscattering enhancement can exist in volume-surface interactions where a double bounce can arise from one volume scattering and one surface scattering. An important quantity to be determined in backscattering enhancement is the angular width. The authors study backscattering enhancement of the volume-surface interaction by performing Monte-Carlo simulations of scattering by vertical dielectric cylinders overlying a dielectric half space using the Foldy-Lax multiple-scattering equations. The results indicate that the angular width of backscattering enhancement for a scattering layer with a small optical thickness is of the order of the wavelength divided by the layer thickness giving an appreciable angular width of the order of 10-30 degrees that can be important for remote sensing applications. The effects of clustering of scatterers leading to collective scattering and absorption effects are also studied View full abstract»

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  • Radar cross-section study of cylindrical cavity-backed apertures with outer or inner material coating: the case of H-polarization

    Publication Year: 1995 , Page(s): 440 - 447
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (640 KB)  

    A dual-series-based solution is obtained for the scattering of an H-polarized plane wave from a slitted infinite circular cylinder coated with absorbing material from inside or outside. For both cases, numerical results are presented for the radar cross section and comparisons are given for two different realistic absorbing materials. The radar cross-section dependencies are also given for the aspect angle of the scatterer and the thickness of the absorbing layer View full abstract»

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  • Rain-rate duration statistics over a five-year period: a tool for assessing slant path fade durations

    Publication Year: 1995 , Page(s): 435 - 439
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    A rain gauge network of 10 tipping bucket rain gauges on the Mid-Atlantic coast of the United States has been in continuous operation since June 1, 1986. Rain-rate distributions and estimated slant path fade distributions at 20 and 30 GHz covering the first five-year period have been derived from the gauge network measurements and published data of Goldhirsh, Krichevsky and Gebo (see ibid., vol.40, no.11, p.1408, 1992). In this article, we present rain-rate time duration statistics. The conversion of rain-rate duration statistics derived from in situ measurements to slant path fade duration statistics is complicated because of the vertical and lateral inhomogeneity of the rain. A benchmark set of fade duration statistics at 20 and 30 GHz for a vertical path is derived from the rain-rate duration statistics employing Crane's (1980) global model. These results may be used by investigators for comparison with and/or conversion to slant path fade duration statistics. Such statistics are important for better assessing optimal coding procedures over defined bandwidths View full abstract»

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IEEE Transactions on Antennas and Propagation includes theoretical and experimental advances in antennas.

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Editor-in-Chief                                                 Kwok W. Leung