By Topic

Antennas and Propagation, IEEE Transactions on

Issue 11 • Date Nov 1994

Filter Results

Displaying Results 1 - 20 of 20
  • Electromagnetic scattering by two parallel dielectric elliptic cylinders

    Publication Year: 1994 , Page(s): 1521 - 1527
    Cited by:  Papers (7)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (464 KB)  

    The transverse magnetic (TM) multiple scattering by two parallel homogeneous dielectric elliptic cylinders is investigated. The solution is an exact one and based on the separation of variables technique in conjunction with the addition theorem for Mathieu functions. It is expressed in terms of a system of simultaneous linear equations of infinite order which is then truncated for numerical computations. Representative numerical results with emphasis on the multiple scattering effects on the backscattering echo width are then generated, for some selected parameters, and presented. It is found that the multiple interactions between the two cylinders affect the echo width significantly View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An investigation of numerical dispersion in the vector finite element method using quadrilateral elements

    Publication Year: 1994 , Page(s): 1502 - 1508
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    The discretization inherent in the vector finite element method results in the numerical dispersion of a propagating wave. The numerical dispersion of a time-harmonic plane wave propagating through an infinite, two-dimensional, vector finite element mesh composed of uniform quadrilateral elements is investigated. The effects on the numerical dispersion of the propagation direction of the wave, the order of the polynomials used for the basis functions, and the electrical size of the elements are investigated. Simple formulas are presented which are excellent approximations to the exact numerical dispersion. The numerical dispersion is validated by a numerical example View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Transient image theory for 2-D and 3-D conducting wedge problems

    Publication Year: 1994 , Page(s): 1515 - 1520
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (360 KB)  

    In the present paper, two- and three-dimensional transient scattering from a perfectly conducting wedge is studied. The exciting sources analyzed are an infinite impulsive line current parallel to edge of the conductor and an arbitrarily oriented electric dipole. The analysis presented is based on the time-harmonic image solution found for the scattered field. The frequency-domain image current corresponding to the field contribution from the wedge is an exact function expressed in terms of simple trigonometric functions. It is dependent only on the coordinates and the amplitude of the source, but it is independent of the observation point. It is shown that the transient scattering can be interpreted as arising from an image source by generalizing the time domain Green's function to complex source points View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • RCS characterization of a finite ground plane with perforated apertures: simulations and measurements

    Publication Year: 1994 , Page(s): 1491 - 1501
    Cited by:  Papers (3)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1032 KB)  

    The monostatic radar cross section of a finite-size perfectly conducting flat plate with perforated apertures is investigated by simulations and measurements. The geometry of a finite ground plane with triangular apertures resembles airplane and automobile windows. The method of moments surface patch formulation is used to compute the radar cross section of a solid plate, a plate with two widely spaced apertures, and a plate with two closely spaced apertures. The characteristics of the triangular patch mesh can impact the accuracy of the computed results with this formulation. The paper presents a methodology to achieve high quality meshes to ensure that the time and convenience gained by developing the general method of moments code is not lost in mesh construction and convergence tests. The results obtained using the method of moments are compared with results obtained by measurements and physical optics. It is shown that the method of moments simulations and measurements are in good agreement. The key features of the influence of the aperture separation on the RCS patterns are discussed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Techniques for evaluating the uniform current vector potential at the isolated singularity of the cylindrical wire kernel

    Publication Year: 1994 , Page(s): 1549 - 1553
    Cited by:  Papers (17)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (428 KB)  

    The cylindrical wire kernel possesses a singularity which must be properly treated in order to evaluate the uniform current vector potential. Traditionally, the singular part of the kernel is extracted resulting in a slowly varying function which is convenient for numerical integration. This paper provides some new accurate and computationally efficient methods for evaluating the remaining singular integral. It is shown that this double integral may be converted to a single integral which no longer possesses a singular integrand and consequently may be efficiently evaluated numerically. This form of the integral is independent of the restrictions involving wire length and radius which are inherent in various approximations. Also presented is a highly convergent exact series representation of the integral which is valid except in the immediate vicinity of the singularity. Finally, a new approximation is derived which is found to be an improvement over the classical thin wire approximation. It is demonstrated that each of these methods provides extremely accurate as well as efficient results for a wide range of wire radii and field point locations View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Scattering of a plane wave by a circular cylinder with uniformly increasing radius

    Publication Year: 1994 , Page(s): 1574 - 1577
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    The interest in the problems of diffraction by moving objects has become obvious due to the applications of nonstationary models for the simulation of different processes. Among them are radar control for the industry ejections or military explosions in the atmosphere and scattering by moving fronts of ionization, or by mobile artificial space objects. The detailed analysis of such processes implies the choice of an adequate model that on the one hand can be effectively investigated but on the other hand ensures a reliable approximation for the complex nonstationary processes. From this point of view, the set of canonical problems that can be solved accurately has great practical significance. We study the diffraction of an electromagnetic plane wave by a circular cylinder with a uniformly increasing radius. The formulation and analysis include propagating singularities as well as the continuous component of the solution. An accurate result is developed by means of separation of variables. Some numerical examples are discussed View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The grounded dielectric layer fed by a current line as a planar microwave applicator

    Publication Year: 1994 , Page(s): 1467 - 1475
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    A planar microwave applicator consisting of a grounded dielectric layer excited by a current line has been theoretically and numerically studied using both a longitudinal spectral representation and a steepest-descent representation. The role of leaky-waves in the description of the near field, and their usefulness in understanding power deposition patterns has been investigated and clarified. Simple design criteria have been found and a general approach has been indicated, that can be applied to the various practical cases View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Multiband frequency selective surface with multiring patch elements

    Publication Year: 1994 , Page(s): 1484 - 1490
    Cited by:  Papers (46)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (504 KB)  

    Theoretical discussions and experimental verifications are presented for a multiband frequency selective surface (FSS) with perfectly conducting multiring patch elements. It is found that the narrow-ring approximation is valid for a ring width less than 0.025λ with λ being the wavelength of the FSS's resonant frequency. A single screen double-ring element FSS is demonstrated for (1) a low-pass FSS that reflects the Ka-band signal while passing the S-, X-, and Ku-band signals, and (2) a tri-band system that reflects the X-band signal while transmitting through the S- and Ku-band signals. In addition, a double screen four-band FSS with non-similar double-ring elements is developed by cascading the above mentioned two single screens. The good agreement obtained between the measured and the computed results verified the computer codes and the approaches of the paper View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Errors due to spatial discretization and numerical precision in the finite-element method

    Publication Year: 1994 , Page(s): 1565 - 1570
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (468 KB)  

    The effects of the spatial discretization and the numerical precision on a plane wave propagating through a finite-element mesh are investigated in this work. The spatial discretization results in dispersion in the amplitude and the phase of the wave and in a non-uniform rate of convergence within an element. The finite precision in the calculations used in a finite-element code results in degraded accuracy. These errors are investigated as a function of the node density, the order of the elements, and the precision of the calculations used in the finite element code. The errors for first- through eighth-order elements are investigated both analytically and numerically View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Physical characteristics of urban micro-cellular propagation

    Publication Year: 1994 , Page(s): 1528 - 1539
    Cited by:  Papers (22)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (1088 KB)  

    The characteristics of the propagation in micro-cellular environments at a carrier frequency of 1.98 GHz are investigated by wide band measurements, complemented by theoretical model calculations. The spatial variations of the complex impulse response were measured with a high time resolution allowing via the scattering function the extraction of detailed information about the wave propagation process. The analysis of a large number of different real propagation configurations leads to a characterization of the most relevant urban micro-cellular propagation mechanisms: propagation in lined streets under line-of-sight conditions, coupling into side streets and propagation effects near street intersections. The wide band channel behavior during the transition of a mobile antenna from directly illuminated into shadowed areas has been considered in particular detail, since this is a crucial situation for a mobile communications system View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Design of planar arrays to obtain efficient footprint patterns with an arbitrary footprint boundary

    Publication Year: 1994 , Page(s): 1509 - 1514
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (460 KB)  

    An antenna pattern synthesis technique is presented that permits the design of planar antenna arrays with footprint patterns of a specified boundary. This technique is applicable to planar arrays of a wide variety of grid structures and can produce patterns with controlled ripple and sidelobe levels. The approach involves two steps: the first consists in stretching the pure real-continuous aperture (an extension of circular Taylor distributions, developed by Elliott and Stern [1990]) into a distribution with a boundary that is inversely proportional to the flat-top beamwidth; the second is the minimization of a cost function (the square of the difference between the resulting power pattern and the desired one) using the Fletcher-Powell method. A square footprint, produced by a rectangular grid (obtained by sampling this distribution) with the corner elements appropriately removed, is presented as an illustration of the method View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • An ultrawideband, polarimetric radar for the study of sea scatter

    Publication Year: 1994 , Page(s): 1461 - 1466
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (568 KB)  

    An ultrawideband radar system is described which has the capability of making pulse-to-pulse polarimetric measurements of the dynamic water features responsible for radar backscatter from the sea. The fast risetime voltage step produced by a Tektronix time-domain reflectometer (TDR) is used to excite a 6-12-GHz amplifier, producing a short (15 cm) radar pulse, A pair of 2- to 18-GHz antennas and appropriate pulse-to-pulse transmit and receive switching capability allows the collection of four consecutive equivalent-time-sampled pulses, one for each combination of the linear transmit and receive antenna polarizations. A polarimetric scattering matrix is then obtained at a sequence of frequencies across the 6-12-GHz band through the Fourier transform of each of the four waveforms and the application of an ultrawideband, polarimetric calibration procedure. The effect of motion on the computed scattering matrix is discussed and quantified, as this is an important consideration for polarimetric investigations of the water features responsible for radar sea scatter, A technique is then presented which compensates for the effects of target translation during the sampling interval. Scattering measurements of several rigid targets and of small breaking waves in a wave tank are used to illustrate the unique capabilities of this system and its applicability to sea scatter studies View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Data extrapolation for high resolution radar imaging

    Publication Year: 1994 , Page(s): 1540 - 1545
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (524 KB)  

    In radar imaging, AR modeling is sometimes used to extrapolate the scattered field data to obtain a high resolution image. In general, the Burg method is used to estimate the prediction parameters. The Burg method leads to a stable prediction filter but can also cause bias in the estimated spectra. One can also use the modified covariance method (MCM) to estimate the prediction parameters. These parameters lead to unbiased spectra. However, the MCM does not guarantee a stable prediction filter. One may have to modify the prediction parameters to ensure a stable prediction filter. One way to ensure stability is to reflect the unstable poles inside the unit circle. It is shown that the modified parameters can be used effectively for data extrapolation. The radar images obtained using this extrapolated data are more accurate than those obtained using the extrapolated data from the Burg prediction parameters View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Anomalous mutual coupling between microstrip antennas

    Publication Year: 1994 , Page(s): 1545 - 1549
    Cited by:  Papers (11)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (468 KB)  

    An asymptotic expansion of the microstrip Green's function is used to facilitate a study of mutual coupling between two printed antennas, and coupling versus element separation is presented for substrate parameters of practical interest. For certain substrate parameters, it is found that the magnitude of mutual coupling does not decay monotonically with increasing element separation. Instead, the magnitude exhibits a quasi-periodic oscillation which can be attributed to the interference of surface and space waves. The presentation and discussion of this anomalous behavior is the purpose of the paper. The asymptotic representation of the Green's function, which differentiates space wave terms from surface wave terms when source and observation points are largely separated, is used to characterize the behavior of mutual coupling in the principal planes View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Equivalent currents for an aperture in an impedance surface

    Publication Year: 1994 , Page(s): 1554 - 1556
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (244 KB)  

    Expressions of equivalent magnetic and electric currents for an aperture in an impedance surface is derived in a self-consistent manner. Each equivalent current consists of the combination of the tangential electric and magnetic fields in the aperture, and is placed in front of the original aperture where the surface is extended to close the aperture. The result is particularly useful for problems involving apertures in an impedance ground plane View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Contour path FDTD method for analysis of pyramidal horns with composite inner E-plane walls

    Publication Year: 1994 , Page(s): 1476 - 1483
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (584 KB)  

    The contour path finite-difference time-domain (FDTD) method is used for modeling pyramidal horn antennas with or without composite E-plane inner walls. To model the pyramidal horn surface, a locally distorted grid is used. Modified equations are obtained based on the locally distorted grid and the assumptions of the contour path method. The developed algorithm is validated by comparing computed antenna gain patterns, with and without the presence of composite material, with available measurements View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Multiple reflections of radio waves in a corridor

    Publication Year: 1994 , Page(s): 1571 - 1574
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (360 KB)  

    New results of radio wave propagation effects in indoor environments for mobile and personal communications are presented. Complex impulse responses and their spatial variations when shifting the mobile antenna were measured with a very high time dispersion resolution. Measured results are compared to results derived from model calculations, using the geometrical description of the environment. The high resolution of the measurement system allows via the scattering function a very detailed analysis of the wave propagation process. This is demonstrated for propagation in a regular corridor (simple cubic geometries). The influence of metallic scatterers in producing multiple reflections like in a large waveguide is shown View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Antenna-reflector combination operating in the Fresnel region at microwave and millimeter-wave bands

    Publication Year: 1994 , Page(s): 1562 - 1565
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (352 KB)  

    A method for calculating antenna-reflector combination gain for rectangular reflectors operating in the Fresnel region is derived instead of an approximate method based on an equi-area circular reflector. The scope of microwave application of the method is discussed, and reflector-equipped microwave links in operation are examined using the new method. A field test result using 50-GHz radio equipment with four types of reflectors shows good agreements with the theoretical calculations View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • Analysis of cavity-backed aperture antennas with a dielectric overlay

    Publication Year: 1994 , Page(s): 1556 - 1562
    Cited by:  Papers (16)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (524 KB)  

    A full-wave analysis of cavity-backed aperture antennas with a dielectric overlay is presented. The theoretical approach uses a closed-form dyadic Green's function in the spectral domain. The aperture equivalent magnetic currents are obtained using the surface equivalence theorem and an integral equation is obtained by matching the fields across the aperture. The moment method applied in spectral domain analysis is employed to solve the integral equation for the equivalent magnetic currents with proper combination of subdomain or entire domain expansion functions. Numerical results include the aperture field distribution and antenna parameters such as input impedance, bandwidth, and efficiency. A set of measurements data is compared with results based on the theoretical work View full abstract»

    Full text access may be available. Click article title to sign in or learn about subscription options.
  • The equivalent parameters for the radiating slot on a sectoral waveguide

    Publication Year: 1994 , Page(s): 1577 - 1581
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (340 KB)  

    Formulas for the field components of the TEpq, mode and the dominant mode TE11 in a sectoral waveguide are given. Using the equivalence principle, the electric field distribution on the aperture surface of a narrow longitudinal slot cut in the curved broad wall of a sectoral waveguide is solved by the moment method (Galerkin's method). Important results such as the scattering parameters, the equivalent shunt admittance, and the resonant conductance and length are studied. The method used in this paper has good precision and has been adopted in the design of a linear slot array 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