By Topic

Antennas and Propagation, IEEE Transactions on

Issue 3 • Date March 1994

Filter Results

Displaying Results 1 - 23 of 23
  • Comments on "An improved pulse-basis conjugate gradient FFT method for the thin conducting plate problem" /spl lsqb/with reply/spl rsqb/

    Publication Year: 1994 , Page(s): 443 - 444
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (185 KB)  

    Peter and Zwamborn comment on the paper by Tran and McCowen (IEEE Trans. Antenn. Propag., vol.41, p.185-90, 1993) which presents pulse-basis expansion functions and Dirac /spl delta/ testing functions within a conjugate gradient FFT (CGFFT) formulation. In the conclusions, Tran and McCowen state: "Although these spurious effects do not appear in the CGFFT formulation using the rooftop basis function proposed by Zwamborn and van den Berg (1991), there are more computational costs associated with their method than with ours." Peter and Zwamborn disagree with this statement. A reply is given by Tran and McCowen.<> View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • EFIE time-marching scattering from bodies of revolution and its applications

    Publication Year: 1994 , Page(s): 412 - 417
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (372 KB)  

    The authors treat the “entire-tangent” representation of a time-domain electric-field integral equation (TDEFIE) for solving transient scattering problems involving perfectly conducting (PEC) bodies of revolution (BOR). This entire-tangent TDEFIE reduces three-dimensional scattering problems with axial symmetry to two-dimensional problems, thus facilitating the numerical treatment and significantly reducing CPU requirements. Additional refinements and algorithm efficiencies are described. Some numerical results and applications are presented View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Infinite phased arrays of cavity-backed patches

    Publication Year: 1994 , Page(s): 390 - 398
    Cited by:  Papers (29)  |  Patents (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (592 KB)  

    An analysis of the radiation properties of infinite phased arrays of probe-fed circular microstrip patches backed by circular cavities using a rigorous Green's function/Galerkin's method is presented. The effect of substrate thickness on both scan volume and bandwidth performance is considered. Results are compared to those of infinite arrays of conventional probe-fed circular patch antennas View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Microwave imaging based on a Markov random field model

    Publication Year: 1994 , Page(s): 293 - 303
    Cited by:  Papers (19)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (808 KB)  

    A new approach to microwave imaging of 2D inhomogeneous dielectric scatterers is presented. The method is developed in the space domain, and Markov random fields are used to obtain a model of the distributions of dielectric features in the scattering region. In this way, a-priori knowledge can be easily inserted in the imaging scheme. This stochastic approach gives rise to a functional equation that can be minimized by using a simulated annealing algorithm. An iterative scheme is derived that allows one to bypass the need for storing large matrices in the computer. Numerical simulation results, confirming the capabilities and effectiveness of the proposed method, are reported. Solutions have generally been obtained in few steps, and seem better than those obtained by other imaging techniques in the space domain. The capability of the algorithm to operate in a strongly noisy environment is also proved View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Bias analysis for ESPRIT-type estimation algorithms

    Publication Year: 1994 , Page(s): 418 - 423
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (436 KB)  

    A statistical analysis using perturbation expansion is applied to the DOA estimation bias for ESPRIT, state-space realization (TAM), and matrix-pencil algorithms, assuming that only a finite amount of array data is available. The authors have obtained an analytical expression for the DOA estimation bias in a simple and self-contained fashion. The tractable formula provides insight to the algorithms. Simulation results verify the analytically predicted performance View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Combining the moment method with geometrical modelling by NURBS surfaces and Bezier patches

    Publication Year: 1994 , Page(s): 373 - 381
    Cited by:  Papers (30)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (648 KB)  

    Induced current distributions on conducting bodies of arbitrary shape modelled by NURBS (non uniform rational B-splines) surfaces are obtained by using a moment method approach to solve an electric field integral equation (EFIE). The NURBS surfaces are expanded in terms of Bezier patches by applying the Cox-de Boor transformation algorithm. This transformation is justified because Bezier patches are numerically more stable than NURBS surfaces. New basis functions have been developed which extend over pairs of Bezier patches. These basis functions can be considered as a generalization of “rooftop” functions. The method is applied to obtain RCS values of several objects modelled with NURBS surfaces. Good agreement with results from other methods is observed. The method is efficient and versatile because it uses geometrical modelling tools that are quite powerful View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Pulsed beam propagation in inhomogeneous medium

    Publication Year: 1994 , Page(s): 311 - 319
    Cited by:  Papers (25)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (728 KB)  

    Pulsed beams (PB) are localized space-time wavepackets that propagate along ray trajectories. This paper deals with general PB solutions in inhomogeneous medium. We derive an approximate form of the time-dependent wave equation (termed the wavepacket equation), valid within a moving space-time window that brackets the wavepacket, and then construct its exact PB solutions. This is done first in a free-space and latter on in a general smoothly varying medium where the propagation trajectories are curved. We also determine the reflection and transmission laws at curved interfaces. These new PBs are related to the so called complex source pulsed beams which are exact solutions in free-space, but they have more general form that admits wavepacket astigmatism and medium inhomogeneity. Since they maintain their wavepacket structure throughout the propagation process they are identified as eigen-wavepacket solutions of the time dependent wave equation View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Response of a grounded dielectric slab to an impulse line source using leaky modes

    Publication Year: 1994 , Page(s): 340 - 346
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (520 KB)  

    Describes how expansions in leaky (or improper) modes may be used to represent the continuous spectrum in an open radiating waveguide. The technique requires a thorough knowledge of the life history of the improper modes as they migrate from improper to proper Riemann surfaces. The method is illustrated by finding the electric field resulting from an impulsively forced current located in the free space above a grounded dielectric slab View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Measured equation of invariance: a new concept in field computations

    Publication Year: 1994 , Page(s): 320 - 328
    Cited by:  Papers (96)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    Numerical computations of frequency domain field problems or elliptical partial differential equations may be based on differential equations or integral equations. The new concept of field computation presented in this paper is based on the postulate of the existence of linear equations of the discretized nodal values of the fields, different from the conventional equations, but leading to the same solutions. The postulated equations are local and invariant to excitation. It is shown how the equations can be determined by a sequence of “measures”. The measured equations are particularly useful at the mesh boundary, where the finite difference methods fail. The measured equations do not assume the physical condition of absorption, so they are also applicable to concave boundaries. Using the measured equations, one can terminate the finite difference mesh very close to the physical boundary and still obtain robust solutions. It will definitely make a great impact on the way one applies finite difference and finite element methods in many problems. Computational results using the measured equations of invariance in two and three dimensions are presented View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Vector finite element formulation for scattering from two-dimensional heterogeneous bodies

    Publication Year: 1994 , Page(s): 357 - 365
    Cited by:  Papers (24)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (676 KB)  

    A formulation is proposed for electromagnetic scattering from two-dimensional heterogeneous structures that illustrates the combination of the curl-curl form of the vector Helmholtz equation with a local radiation boundary condition (RBC). To eliminate spurious nonzero eigenvalues in the spectrum of the matrix operator, vector basis functions incorporating the Nedelec constraints are employed. Basis functions of linear and quadratic order are presented, and approximations made necessary by the use of the local RBC are discussed. Results obtained with linear-tangential/quadratic normal vector basis functions exhibit excellent agreement with exact solutions for layered circular cylinder geometries, and demonstrate that abrupt jump discontinuities in the normal field components at material interfaces can be accurately modeled. The vector 2D formulation illustrates the features necessary for a general three-dimensional implementation View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Parametric oscillation in nonlinear dipole arrays

    Publication Year: 1994 , Page(s): 406 - 411
    Cited by:  Papers (2)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    An experimental investigation of large nonlinear dipole arrays is presented, using a diode-loaded dipole placed between two parallel conducting plates. Using this topology the authors were able to demonstrate enhanced conversion efficiency into the second harmonic and obtain spontaneous parametric oscillation for certain array geometries. Parametric oscillation was achieved by strongly driving the antenna at a single pump frequency and adjusting the cavity length for resonance at a subharmonic. A pump threshold for parametric down-conversion was observed, below which no sub-harmonics were produced. These results suggest using quasi-optical techniques for frequency multiplication and parametric up-conversion or amplification View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Complex multipole beam approach to electromagnetic scattering problems

    Publication Year: 1994 , Page(s): 366 - 372
    Cited by:  Papers (25)  |  Patents (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (596 KB)  

    A novel approach to reducing the matrix size associated with the method of moments (MoM) solution of the problem of electromagnetic scattering from arbitrary shaped closed bodies is presented. The key step in this approach is to represent the scattered field in terms of a series of beams produced by multipole sources located in a complex space. On the scatterer boundary, the fields generated by these multipole sources resemble the Gabor basis functions. By utilizing the properties of the Gabor series, guidelines for selecting the orders as well as locations of the multipole sources are developed. It is shown that the present approach not only reduces the number of unknowns, but also generates a generalized impedance matrix with a banded structure and a low condition number. The accuracy of the proposed method is verified by comparing the numerical results with those derived by using the method of moments View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Compact conical antennas for wide-band coverage

    Publication Year: 1994 , Page(s): 436 - 439
    Cited by:  Papers (14)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB)  

    A broadband antenna with a vertically polarized, omnidirectional electric field is studied. The design of the antenna and its feeding system in the wide frequency range from 20 to 1000 MHz is described and the driving-point impedance determined. Also calculated are the voltage standing-wave ratio (VSWR) and the input impedance of a transmission line connected to the antenna. More efficient operation at low frequencies is obtained by adding a length of transmission line to form a resonant section with the antenna. The effect of the different properties of the earth's surface on the field pattern is treated in a companion paper View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Broad-band characterization of millimeter-wave log-periodic antennas by photoconductive sampling

    Publication Year: 1994 , Page(s): 335 - 339
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (476 KB)  

    Results of photoconductive sampling measurements used to characterize millimeter-wave log-periodic antennas with continuous, simultaneous frequency coverage from 10 to 300 GHz are presented. Polarization properties are investigated employing wire-grid polarizers. This study reveals new information on structure resonances and antenna polarization View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • MM-Wave integrated phased arrays with ferrite control

    Publication Year: 1994 , Page(s): 304 - 310
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (616 KB)  

    A new class of electrically scanned antenna arrays for the millimeter wave range is described. The antenna is based on a planar integrated ferrite travelling wave structure and is controlled by the magnetization of ferrite elements. Experimental antennas operating in the 8-mm wave range have the following electrical parameters: beamwidth 2 to 4°, two dimensional scanning ±20°, loss about 3 to 4 dB View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • RCS measurements, transformations, and comparisons under cylindrical and plane wave illumination

    Publication Year: 1994 , Page(s): 329 - 334
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (500 KB)  

    Monostatic RCS measurements of a long bar (at X-band) and of a scale model aircraft (at C-band) were performed under the quasi-plane wave illumination produced by a dual parabolic-cylinder CATR. At Arizona State University's ElectroMagnetic Anechoic Chamber (EMAC) facility, these measurements were repeated under the cylindrical wave illumination produced by a March Microwave Single-Plane Collimating Range (SPCR). The SPCR measurements were corrected using the “reference target method.” the corrected SPCR measurements are in good agreement with the CATR measurements View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A new formulation for the design of Chebyshev arrays

    Publication Year: 1994 , Page(s): 439 - 443
    Cited by:  Papers (16)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (404 KB)  

    A new formulation for the design of Chebyshev arrays is presented which makes no direct use of Chebyshev polynomials. The array factor is expressed in terms of cosine/cosine-hyperbolic functions based on which all analysis and design steps are carried out. Zeros of the array factor are used to obtain a system of equations for excitation currents. Solving this system of equations, current magnitudes are determined in terms of the current of one element chosen as the independent variable. A general formulation for an even or odd but otherwise arbitrary number of elements is presented. The minimum number of elements required to achieve the desired beamwidth and side lobe level is obtained in a single step without resorting to an iterative process. The optimum spacing between elements for broadside and end fire arrays is also addressed. Numerical results for example cases are provided View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Analysis of microstrip antennas on a curved surface using the conformal grids FD-TD method

    Publication Year: 1994 , Page(s): 423 - 427
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (448 KB)  

    The need for small, portable antennas for mobile communications has spurred the study of microstrip antennas (MSA). MSA are quite flexible and have been used as conformal antennas on arbitrary curved surfaces. The characteristics of conformal MSA can be expected to differ from those of planar models. Dependable numerical analyses will obviate many of the costs and other inconveniences associated with experiments, but as antennas may be mounted on surfaces of arbitrary topological complexity, analysis methods must have a general applicability. The curvilinear finite-difference time-domain (FD-TD) method has shown excellent versatility. This method is applied to analyze microstrip antennas mounted on curved surfaces. The numerical predictions are compared with the experimental values. The results confirm the predictions within acceptable limits and appear to confirm the validity of the method. As a result, it was confirmed that the input impedance and directivity of MSA on curved surfaces are different from the flat MSA View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Impedance behaviour and scan performance of microstrip patch array configurations suitable for optical beam forming networks

    Publication Year: 1994 , Page(s): 432 - 435
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (368 KB)  

    The authors propose two microstrip array configurations suitable for integration with optical beam forming networks. Rigorous full wave analyses of both array configurations, based on the spectral domain technique and incorporating accurate modelling of the coaxial feeds are implemented to investigate the impedance behaviour, scan performance, beam efficiency and cross polarization levels of each proposed array View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • A method to reduce stray signal errors in antenna pattern measurements

    Publication Year: 1994 , Page(s): 399 - 405
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (528 KB)  

    The presence of stray signals in an antenna measurement range can cause errors in the measured patterns. In order to measure low sidelobe antennas in an antenna range, the stray signals in the range should be very small (at least 8-10 dB below the sidelobe level). It may not be possible to achieve such low level stray signals in a real world antenna range. Thus, alternate methods for reducing these measurement errors are needed. In this paper, such a method is presented. Using simulated examples and experimental data, it is shown that this method significantly reduces the chamber related measurement errors. The method can also be used to identify the angular regions along which the stray signal errors are most significant. Thus, the range can be qualified and, if possible, improved View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • High frequency approximations to the physical optics scattering integral

    Publication Year: 1994 , Page(s): 427 - 432
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (552 KB)  

    Discusses two high frequency (HF) approximations to the physical optics (PO) scattering integral for the far field radar backscatter from a general curved edged reflecting surface viewed at arbitary aspect. The PO scattering integral is first approximated as the sum of a specular effect and an edge effect, where the latter is represented explicitly as a certain line integral evaluated over the boundary edge of the reflector. A closed form result is then obtained by applying the method of stationary phase to the line integral. With the exception of singularities that can occur at caustics, or when the specular point falls on the boundary edge, these HF approximations are found to work reasonably well for smooth surfaces whose Gaussian curvatures have constant sign (positive or negative, but never zero) View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The electromagnetic field of a vertical electric dipole over the Earth or sea

    Publication Year: 1994 , Page(s): 382 - 389
    Cited by:  Papers (21)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (500 KB)  

    The analysis of King (1990) of the electromagnetic field of a vertical electric dipole over an imperfectly conducting half-space is applied to obtain the far field when the dipole is at a specified height d. The contributions by the space wave with its 1/r dependence and the lateral surface wave with its 1/r2 dependence are separated and studied in detail when the dipole is over a wide range of media such as sea water, wet and dry Earth, lake water and dry sand. Graphs of the far-field patterns are shown View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Scattering of radiowaves by a melting layer of precipitation in backward and forward directions

    Publication Year: 1994 , Page(s): 347 - 356
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (808 KB)  

    A melting layer of precipitation is composed of melting snowflakes (snow particles); the assumption of spherical particles along with mass conservation is used. The melting layer is studied by deriving the size distribution of the melting snow particles, the thickness of a melting layer, the density of a dry snow particle, and the average dielectric constant of a melting snow particle. Vertical profiles of radar reflectivity and specific attenuation are computed at 1-100 GHz by using the Mie theory for five raindrop size distributions at rain rates below 12.5 mm/h. The radar bright band is explained with computed radar reflectivities at 3-10 GHz. It is shown that the radar bright band can be absent in the melting layer at frequencies above 20 GHz. This agrees with radar observations at 35 and 94 GHz. The specific attenuation, as well as the average specific attenuation of the melting layer, is divided into absorption part and scattering part. The latter is increasingly significant with the increase of frequency. The total zenith attenuation due to stratiform rain is divided into the rain zenith attenuation and the additional zenith attenuation, which is the difference between zenith attenuation, due to the melting layer, and attenuation, due to the same path length of the resulting rain. The additional zenith attenuation increases with the increase of rain rate even at frequencies above 20 GHz. This should be taken into account in radar remote sensing and satellite-Earth communications 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