By Topic

Antennas and Propagation, IEEE Transactions on

Issue 4 • Date Apr 1991

Filter Results

Displaying Results 1 - 22 of 22
  • The polarization of a complex vector in higher dimensions

    Publication Year: 1991 , Page(s): 555 - 556
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (168 KB)  

    The use of trigonometric identities facilitates the determination of the polarization of a vector quantity in two dimensions, but becomes rapidly unwieldy in higher dimensions. Instead, the polarization can be obtained from simple algebraic considerations when the problem is viewed as an eigenvalue-eigenvector problem. The authors derive the formulas, show that, regardless of the dimension, the eigenvalue may assume at most only two values, and conclude that because of this fact, the polarization of a complex vector is a two-dimensional concept with no higher dimensional analog View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Achromatic doublets for Gaussian beams

    Publication Year: 1991 , Page(s): 559 - 562
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (300 KB)  

    The properties of doublets of thin lenses in the Gaussian optics approximation were investigated. Two different ways for such a doublet to give strictly achromatic images of the input beam waist were found. Both solutions may be useful in a variety of applications, one being the possibility of shaping asymmetrical beams for fan beam antennas illumination. Using modes higher than the fundamental mode will allow the design of more realistic focal systems View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Electromagnetic scattering by and transmission through a three-dimensional slot in a thick conducting plane

    Publication Year: 1991 , Page(s): 543 - 550
    Cited by:  Papers (43)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (504 KB)  

    A hybrid numerical technique for a characterization of the scattering and transmission properties of a three-dimensional slot in a thick conducting plane is presented. The technique combines the finite element and boundary integral methods to formulate a system for the solution of the aperture fields and by virtue of the finite element method, it is applicable to inhomogeneously filled slots of arbitrary shape. The numerical implementation is described for the edge-based expansion functions associated with rectangular brick elements, and examples are presented demonstrating the validity, versatility, and capability of the technique. These also provide some understanding of the slots scattering and transmission properties as a function of its geometry and material filling View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A new structure for adaptive broad-band beamforming

    Publication Year: 1991 , Page(s): 551 - 555
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (364 KB)  

    The performance characteristics of adaptive array systems with derivative constraints have been investigated by several authors. As a result of the derivative constraints, the array beamwidth in the look direction could be made as broad as desired; however, this increased beamwidth was achieved at the price of reducing array gain. A structure is proposed for an adaptive broadband beamforming system in a manner that can produce a broader beamwidth in the look direction without any derivative constraints imposed on the adaptive processor. Compared to the conventional Frost beamformer with derivative constraints, the computer simulations illustrate the effectiveness of the proposed structure, which broadens the beamwidth in the look direction with only slight sacrifice of array gain View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A novel theory for dielectric-inset waveguide leaky-wave antennas

    Publication Year: 1991 , Page(s): 497 - 504
    Cited by:  Papers (27)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (556 KB)  

    A type of leaky-wave antenna that is particularly suitable for applications in the millimeter-wave range is analyzed. The objective of this work is to provide a practical and accurate theory for the design of this class of antennas. The analysis procedure is based on the development of a novel, multimode transverse equivalent network representation. All mutual coupling effects are rigorously taken into account. A single dispersion relation is derived via a transverse resonance procedure, and the complex dispersion behavior of the antenna is obtained through its numerical solution. Useful approximate initial design formulas are given, and a detailed parametric analysis is carried out, showing the effects of changes of all the structural parameters. The results obtained indicate that the structure, in addition to being mechanically simple to realize, exhibits a very flexible electrical behavior. The theory developed, therefore, is a powerful tool for the design and optimization of this class of antennas View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Statistically thinned arrays with quantized element weights

    Publication Year: 1991 , Page(s): 436 - 447
    Cited by:  Papers (24)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (868 KB)  

    The use of statistical thinning and quantized element weights to produce low sidelobe patterns using large circular array apertures is investigated. The major results of the analysis show that by using either of several thinning algorithms it is possible to obtain substantial sidelobe reduction by a combination of statistical thinning and the use of discrete amplitude quantization. The paper includes generalized formulas for sidelobe level, EIRP (effective isotropic radiated power), and curves to show how these parameters vary as a function of the design sidelobe level for the selected Taylor pattern View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • High frequency scattering from corrugated stratified cylinders

    Publication Year: 1991 , Page(s): 512 - 520
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (644 KB)  

    Interest in applying radar remote sensing for the study of forested areas led to the development of a model for scattering from corrugated stratified dielectric cylinders. The model is used to investigate the effect of bark and its roughness on scattering from tree trunks and branches. The outer layer of the cylinder (bark) is assumed to be a low-loss dielectric material and to have a regular (periodic) corrugation pattern. The inner layers are treated as lossy dielectrics with smooth boundaries. A hybrid solution based on the moment method and the physical optics approximation is obtained. New expressions for the equivalent physical-optics currents are used which are more convenient than the standard ones. It is shown that the bark layer and its roughness both reduce the radar cross-section. It is also demonstrated that the corrugations can be replaced by an equivalent anisotropic layer View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An efficient formulation to determine the scattering characteristics of a conducting body with thin magnetic coatings

    Publication Year: 1991 , Page(s): 448 - 454
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (528 KB)  

    Two new and efficient surface integral equations, derived from corresponding volume integral equations, are developed to calculate the scattering of electromagnetic (EM) waveform from an arbitrarily shaped conducting body coated with thin lossy magnetic film. Their numerical solutions by the method of moments (MM) for two-dimensional structures with full or partial coatings are presented. It is shown that the radar cross-section of a conducting body can be significantly reduced by coating it with a lossy magnetic film. To verify the validity and accuracy of the proposed formulation, another method based on the expansion of cylindrical harmonic functions with real arguments is also developed to calculate the scattering of a plane EM wave from an electrically large coated circular cylinder. The same problem was also solved by the proposed formulation, and excellent agreement between the two approaches was achieved. In addition, numerical results of the scattering from a rectangular coated cylinder is shown to be consistent with that obtained by a modified finite-difference-time-domain (FDTD) method View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The interpanel gap scattering effect in a compact range

    Publication Year: 1991 , Page(s): 480 - 484
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (436 KB)  

    An analytical approach coupled with experimental determination of a key parameter has been developed to quantify the effect of the interpanel gap scattering in a compact range. The results show the effect of scattering on the copol and x-pol field distribution in the quiet zone area. The effect of the gap scattering can be regarded as an additional root mean square error on the antenna surface accuracy View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Bandwidth performance of 16-element thinned phased array with tapped delay-line filter

    Publication Year: 1991 , Page(s): 562 - 565
    Cited by:  Papers (5)  |  Patents (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (260 KB)  

    The bandwidth performance of a thinned phased adaptive array with and without a delay-line processor are compared. Five- and nine-jammer scenarios are considered for two EHF bands, 0.125 and 2.0 GHz. The null-depth which was used as the measure of performance was computed over the nulling band for three different delay-line configurations. The simulation results give some insight into the way in which delay-line compensation provides improved performance as the interference bandwidth increases View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Oblique scattering from inhomogeneous cylinders using a coupled integral equation formulation with triangular cells

    Publication Year: 1991 , Page(s): 485 - 490
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (492 KB)  

    A novel method of moments formulation for scattering from penetrable two-dimensional cylinders illuminated by an obliquely incident excitation is presented. The permittivity and permeability profiles may have arbitrary piecewise-constant dependence on the transverse variables. Regardless of the polarization of the incident field, the response of the scatterer is a combination of transverse electric (TE) and transverse magnetic (TM) waves. Coupled integral equations for the longitudinal electric and magnetic fields are used in conjunction with a triangular-cell discretization, a piecewise linear representation for Ez and Hz, and point-matching. Numerical results for the internal fields and scattering cross-section are presented to illustrate the accuracy of the approach View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A finite-difference time-domain near zone to far zone transformation [electromagnetic scattering]

    Publication Year: 1991 , Page(s): 429 - 433
    Cited by:  Papers (101)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (372 KB)  

    An efficient time-domain near-zone-to-far-zone transformation for FDTD (finite-difference-time-domain) computations is presented. The approach is to keep a running accumulation of the far-zone time-domain vector potentials due to the tangential electric and magnetic fields on a closed surface surrounding the scatterer at each time step. At the end of the computation, these vector potentials are converted to time-domain far-zone fields. Many far-zone bistatic directions can be included efficiently during one FDTD computational run. Frequency domain results can be obtained via fast Fourier transform. Wideband results for scattering from a perfectly conducting plate were obtained from a single FDTD computation transformed to the frequency domain, and compared with moment method results. This approach is significantly more efficient than computing many FDTD results using sinusoidally varying excitation if a wide frequency band is of interest. Coupled with recent advances in computing FDTD results for frequency-dependent materials, wideband results for far-zone scattering from targets including frequency-dependent materials can be obtained efficiently View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Early-time currents induced on a cylinder by a cylindrical electromagnetic wave

    Publication Year: 1991 , Page(s): 455 - 463
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (556 KB)  

    An analytical study of the early-time current response of a perfectly conducting circular cylinder to a cylindrical electromagnetic wave, produced by a parallel filament carrying a unit-step current, is presented. Surface current density expressions for both the shadow and illuminated regions are obtained by applying the Watson transformation to the frequency-domain solution and then evaluating the corresponding integrals separately, in the shadow region by a residue series and in the illuminated region by using the saddle point technique. Analytical results obtained by using a double Laplace transform approach for the shadow region and the Luneberg-Kline expansion approach for the illuminated region are given. Numerical results illustrate the variation of the distribution of current density with time for different locations of the line current with respect to the cylinder, and also allows a comparison of the alternate methods applied by the authors, showing their corresponding range of validity. The response to an impulsive plane wave is derived as a special case View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • ALTAIR VHF/UHF observations of multipath and backscatter enhancement

    Publication Year: 1991 , Page(s): 528 - 534
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (656 KB)  

    During the Defense Nuclear Agency (DNA) PEAK (propagation effects assessment-Kwajalein) experiment in August 1988, the ALTAIR VHF/UHF wide bandwidth radar was used to track spherical satellites in low-earth orbit. The purpose of the experiment was to obtain radar data during the most severe natural propagation disturbances. The PEAK experiment was successful, giving many measurements of strong scintillation as well as the first measurements of frequency-selective fading on propagating radar pulses. Experimental results are used to demonstrate an enhancement, due to scattering, in the average received power that is observed during severe scintillation. The observed statistics of the enhancement are compared to analytic calculations using the Nakagami-m distribution with very good agreement View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The exact kernel for cylindrical antenna

    Publication Year: 1991 , Page(s): 434 - 435
    Cited by:  Papers (27)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (88 KB)  

    In the numerical calculation for a cylindrical antenna, the thin-wire kernel is widely used as a convenient approximation to the exact kernel of the electric-field equation. However, this thin-wire approximation is valid only if the radius of wire is much less than its length and the wavelength; furthermore, arbitrarily using this approximation may not obtain the convergent outcomes. The expression of the exact kernel for the cylindrical antenna, which would be useful in the numerical work, is presented View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On the performance of adaptive Gram-Schmidt algorithm for interference cancelling arrays

    Publication Year: 1991 , Page(s): 505 - 511
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (516 KB)  

    A detailed performance analysis of the least mean square (LMS) algorithm to update each stage of an adaptive Gram-Schmidt processor in interference cancelling adaptive arrays is presented. It is shown that although the number of adaptive weights in the processor is proportional to M2. the total misadjustment contributed by weight jittering is proportional to only M, where M is the size of the processor. In absolute terms, the weight jittering noises do not accumulate as would be expected, but cancel one another out and decrease in magnitude as the optimal powers become smaller from one processing stage to the next. For optimal performance, the feedback factors used in the individual LMS loops should be normalized so that the amount of misadjustment contributed and the convergence time constant are the same for all processing stages. All the weights belonging to one processing stage must be adjusted in a synchronous manner with the same input vector. This synchronous updating requirement is essential for the cancellation of the jittering noises, although in situations where the weights are adaptively updated in a time-multiplexed manner, it may appear more efficient to update each weight based on the most current inputs View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • On the variational aspects of the moment method [electromagnetics]

    Publication Year: 1991 , Page(s): 473 - 479
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (576 KB)  

    The variational properties of the moment method as applied via the electric field integral equation (EFIE) to perfectly conducting radiators and scatterers with time-harmonic excitation are discussed. It is shown that the admittance, impedance, gain and radar cross-section can be expressed in terms of the self-reaction or the mutual reaction of the electric current distribution induced on the body. Subject to the above restrictions and assuming the usual reciprocity theorems are applicable, it is shown that the reaction is stationary with Galerkin's method, but it is not when the non-Galerkin moment method is applied in the customary manner. Numerical results are included to compare the performance of the variational and nonvariational moment method View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Synthesis of offset parabola with open-ended waveguides feed

    Publication Year: 1991 , Page(s): 535 - 542
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    The synthesis of an offset parabola with array feeds consisting of open-ended waveguides located around the focal point of the reflector is investigated. The approach is based on simulated annealing which has been applied to the analysis to two-dimensional phased arrays. Two cases of aperture distributions, uniform and Taylor with 30-dB sidelobe level, are discussed. Both results seem to be satisfactory View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Beam diffraction by planar and parabolic reflectors

    Publication Year: 1991 , Page(s): 521 - 527
    Cited by:  Papers (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (496 KB)  

    In the complex source point technique, an omnidirectional source diffraction solution becomes that for a directive beam when the coordinates of the source position are given appropriate complex values. This is applied to include feed directivity in reflector edge diffraction. Solutions and numerical examples for planar strip and parabolic cylinder reflectors are given, including an offset parabolic reflector. The main beams of parabolic reflectors are calculated by aperture integration and the edge diffracted fields by uniform diffraction theory. In both cases, a complex source point feed in the near or far field of the reflector may be used in the pattern calculation, with improvements in accuracy in the lateral and spillover pattern lobes View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Design trades for Rotman lenses

    Publication Year: 1991 , Page(s): 464 - 472
    Cited by:  Papers (25)  |  Patents (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (456 KB)  

    The foundation of a satisfactory Rotman lens design is geometric. The effects of seven design parameters (focal angle, focal ratio, beam angle ratio, maximum beam angle, beam port curve ellipticity, array element spacing, and focal length/λ) on the shape, and on the geometric phase and amplitude errors of a Rotman lens are described. The advantage of beam port shaping to reduce phase error, and of pointing port horns at the opposite apex (instead of normal to the curve) to reduce off-axis beam amplitude asymmetries, are shown numerically. A design procedure for selecting these parameters is given, and a calculation of lens gain is presented View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Moment-method analysis of large, axially symmetric reflector antennas using entire-domain functions

    Publication Year: 1991 , Page(s): 491 - 496
    Cited by:  Papers (18)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (400 KB)  

    The moment-method technique utilizing entire domain basis functions is applied to the analysis of large, axially symmetric reflector antennas. The electric surface current is modeled as a finite series of sinusoids whose domain consists of the entire generating curve. This expansion results in a matrix size of less than 5% of that produced with subdomain basis functions. Only a slight increase in the CPU requirements occurs from this analysis. The results from this technique show good agreement when compared to both physical optics and a subdomain-based moment-method formulation on small, axially fed paraboloidal and hyperboloidal reflector antennas. Extension to a large 100-λ paraboloidal reflector with f/D=0.4 produces results comparable to that obtained using physical optics. Convergence is obtained with as few as two expansion terms per wavelength. Discretization of the generating curve with four points per wavelength leads to results which agree within 0.5 dB over data from a more densely defined curve View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An efficient representation of radiation from a circular aperture with tapered amplitude and quadratic phase

    Publication Year: 1991 , Page(s): 556 - 559
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (264 KB)  

    An efficient series representation is derived for Ipab, a quadratic phase integral commonly encountered in aperture-antenna theory. The accuracy and efficiency of the series formula relative to ordinary numerical integration are discussed. This formula may be useful in solving such problems as quadratic-phase error effects on beamwidth, field in the Fresnel-region, on-axis defocus characteristics of a paraboloidal reflector, or shadow-region field behind a disk View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.

Aims & Scope

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

Full Aims & Scope

Meet Our Editors

Editor-in-Chief                                                 Kwok W. Leung