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Antennas and Propagation, IEEE Transactions on

Issue 2 • Date Feb 1990

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Displaying Results 1 - 22 of 22
  • Complex resonances of conducting spheres with lossy coatings

    Publication Year: 1990 , Page(s): 236 - 240
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (356 KB)  

    The electromagnetic scattering amplitude for metal objects coated with a lossless dielectric exhibits a large number of resonances versus real frequency. These resonances are a function of the object shape and size, coating thickness, and coating electrical properties. Previously, it was shown that for coated spheres and nonspherical bare objects, these resonances can be understood in terms of phase matched circumnavigating surface waves and the objects' complex eigenfrequencies. The effect of dielectric loss in the coating on the complex eigenfrequencies and phase velocities of these surface waves is presented for a metal sphere coated with a uniform homogeneous dielectric coating. It is seen that the positions of the complex resonance frequencies move away from the real frequency axis under the influence of dielectric loss in the coating. The effect of this is shown to correspond to the changes in the backscatter spectrum versus real frequency as computed using a Mie series expansion. The significant difference between the lossless and lossy dielectric-coated sphere cases is seen to be due to a modification of the phase velocities of surface waves, particularly the whispering gallery types, and the increased attenuation of the surface wave modes View full abstract»

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  • Time-domain analysis of the Sommerfeld VMD problem based on the exact image theory

    Publication Year: 1990 , Page(s): 241 - 250
    Cited by:  Papers (12)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (612 KB)  

    A novel time-domain solution of the Sommerfeld half-space problem is constructed through the exact image theory. The radiation from a vertical magnetic dipole (VMD) above the planar interface of two lossless and dispersionless dielectric media is analyzed. The reflection field is given as a Laplace transform when the refraction index of the lower medium is greater. The converse case of refraction indexes is also studied, and the reflection field is written as originating from an image source located in homogeneous space. The present theory is seen to lead to a numerically efficient result, which is demonstrated with examples View full abstract»

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  • Coupling into and scattering from cylindrical structures covered periodically with metallic patches

    Publication Year: 1990 , Page(s): 220 - 226
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (528 KB)  

    Circular cylindrical structures covered periodically with metallic patches are considered. After an analogy to planar periodic surfaces is shown, formulations are presented for calculating induced currents on the curved surface. The equations are solved and results calculated for the specific case of periodic strips on the cylindrical surface. For a cylindrical structure a two-dimensional periodicity exists, as in a planar structure, while a spherical structure allows only a rotational periodicity. When the cylindrical structure is excited by the characteristic harmonic of the system, the spectral response of the transmitted field exhibits resonances that depend on the surface periodicity, as is known for planar structures. Since the cylindrical structure contains finite closed regions, the effects of resonances internal to the structure are seen and give additional information as compared to planar structures View full abstract»

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  • Radiation and scattering in homogeneous general biisotropic regions

    Publication Year: 1990 , Page(s): 227 - 235
    Cited by:  Papers (27)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (676 KB)  

    Solutions to Maxwell's equations for a four-parameter biisotropic medium are analyzed. A field decomposition provides remarkable simplification in the derivation of solutions and provides a qualitative picture of biisotropy. Green's dyadics and the Cherenkov radiation description are easily derived. A broad class of biisotropic materials that is not optically active is found (for instance, Cherenkov radiation and dipole radiation are linearly polarized). Green's dyadics for a more general constitutive relation, which includes diffusion terms, are solved in terms of the biisotropic solutions. Huygens' principle is obtained and applied in surface integral equation form to the problem of a thin linear antenna in order to demonstrate the feasibility of upgrading existing numerical codes to handle the case of biisotropic materials View full abstract»

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  • Improved adaptive-beamforming target for self-calibrating a distorted phased array

    Publication Year: 1990 , Page(s): 186 - 194
    Cited by:  Papers (20)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (624 KB)  

    An improved adaptive beamforming procedure is presented for self-calibrating a distorted phased array. The multiple scatterer algorithm (MSA) combines the echoes from several range bins to synthesize a beamformer that is less perturbed by clutter than the basic dominant scatterer algorithm (DSA). It was tested using experimental microwave echoes from industrial sites near Phoenixville, PA. It was found that the MSA can synthesize a nearly ideal beamformer using the echoes from three range bins having good beamformers, and that it can improve the image quality using the echoes from three bad beamformers, each of which is incapable of phase cohering the array by itself View full abstract»

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  • Inflection point caustic problems and solutions for high-gain dual-shaped reflectors

    Publication Year: 1990 , Page(s): 202 - 211
    Cited by:  Papers (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (724 KB)  

    The singular nature of the UTD (uniform geometrical theory of diffraction) subreflector scattered field at the vicinity of the main reflector edge (for a high-grain antenna design) is investigated. It is shown that the singularity in the UTD edge-diffracted and slope-diffracted fields is due to the reflection distance parameter approaching infinity in the transition functions. While the GO (geometrical optics) and UTD edge-diffracted fields exhibit singularities of the same order, the edge slope-diffracted field singularity is more significant and is substantial for greater subreflector edge tapers. The diffraction analysis of such a subreflector in the vicinity of the main reflector edge has been carried out efficiently and accurately by a stationary phase evaluation of the φ-integral, whereas the θ-integral is carried out numerically. Computational results from UTD and PO (physical optics) analysis of a 34-m ground station dual-shaped reflector confirm the analytical formulations for both circularly symmetric and offset asymmetric subreflectors. It is concluded that the proposed POθGOφ technique can be used to study the spillover or noise temperature characteristics of a high-grain reflector antenna efficiently and accurately View full abstract»

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  • Robust perturbation algorithms for adaptive antenna arrays

    Publication Year: 1990 , Page(s): 195 - 201
    Cited by:  Papers (13)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (492 KB)  

    The generation of a perturbation sequence for an adaptive beamformer is described. This perturbation sequence permits simultaneous adaption and reception by use of weight perturbations that do not obstruct the look direction constraint. It is shown that this sequence is generally shorter in length than previously described sequences and offers scope for computational savings through reduction of the number of projection operations required. Convergence in the mean of the resulting adaptive algorithm is demonstrated. Experiments conducted using a four-element linear array operating in the MW RF range have confirmed that the predicted results are achievable under the nonideal conditions of quantized array weights and finite word length arithmetic View full abstract»

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  • Oblique scattering from lossy strip structures with one-dimensional periodicity

    Publication Year: 1990 , Page(s): 212 - 219
    Cited by:  Papers (11)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (532 KB)  

    The intentional addition of loss to a periodic structure can be used as a technique to alter its scattering characteristics. The problem of an oblique plane wave incident on an array with one-dimensional periodicity is examined. The unit cell of the array is composed of a number of thin resistive strips. The obliqueness of the incident plane wave combined with the lossy nature of the structure causes the transverse electric (TE) to zˆ and the transverse magnetic (TM) to zˆ fields to couple. To analyze the described problem, two coupled electric field integral equations that have as unknowns the equivalent surface currents on the strips in the unit cell are derived. The integral equations are discretized and solved approximately using the method of moments with subdomain basis and testing functions. The periodic Green's function is efficiently calculated using the Poisson summation formula. The interaction of the structure with the surrounding environment is described in terms of a generalized scattering matrix. Results are presented showing the TE/TM coupling behavior as strip resistance is increased for representative structures View full abstract»

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  • A general theory on the graphical representation of antenna-radiation fields

    Publication Year: 1990 , Page(s): 160 - 165
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (572 KB)  

    A general theory for graphical representation of antenna radiated fields is developed. The application of the method to the special case of a transverse electromagnetic-mode-excited biconical antenna is investigated in detail. Electric field lines in the r-ϑ plane of a spherical coordinate system are presented in a manner such that the same electric flux is always carried between two neighboring field lines. Thus, their mutual distance is a criterion for the strength of the local electric field. The differential equations which govern the displacement of a field point are derived and solved. The time-dependent evolution of a field-line pattern is examined in detail. The new theory for graphical field representation permits, in an elegant manner, the analysis of the transmission and receiving mechanism of arbitrary antenna configurations. Thus, it is suggested that an iterative graphical synthesis procedure could, in the future, be applied to the computer-aided design modeling of antenna shapes View full abstract»

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  • Measuring the propagation properties of a forest canopy using a polarimetric scatterometer

    Publication Year: 1990 , Page(s): 251 - 258
    Cited by:  Papers (10)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (604 KB)  

    A truck-mounted 1.6-GHz polarimetric scatterometer was used from a 19-m high platform to measure the backscattering from a dense canopy of pine trees at an incidence angle of 40°. Two sets of measurements were made at each of many spatial locations, one set with and the other without a trihedral corner reflector present on the ground surface underneath the canopy. From the two sets of polarimetric measurements, it was possible to determine the mean values and the statistical distributions of the canopy attenuation factors for horizontal and vertical polarizations. The mean values of the one-way attenuation factors were found to be 9.31 dB for horizontal polarization and 9.16 dB for vertical polarization. The precision associated with the values of the canopy loss factor measured using the polarimetric technique is estimated to be on the order of ±0.3 dB View full abstract»

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  • Mobile satellite system propagation measurements at L-band using MARECS-B2

    Publication Year: 1990 , Page(s): 259 - 264
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (488 KB)  

    A mobile satellite system (MSS) propagation experiment at 1.5 GHz was performed near the east coast of the United States in central Maryland during December 1987 using the MARECS-B2 satellite as a transmitter platform. A receiving system in a vehicle measured signal fades caused by shadowing and multipath from roadside trees and utility poles. The propagation degradations were characterized for a system of three roads previously examined using a helicopter as the transmitter platform. The objectives of the MARECS-B2 MSS tests were to: (1) establish cumulative fade distributions for the particular satellite geometry for both rural and suburban roads; (2) validate the consistency of previous roadside tree measurements which employed a helicopter as the transmitter platform for the same system of roads; (3) obtain an additional set of fade levels at a lower angle hitherto not measured in central Maryland; and (4) combine the satellite-acquired data set with previous helicopter results and establish an analytic, empirically derived function describing the cumulative fade distributions for a family of path angles. An analysis of the satellite data has demonstrated the successful achievement of these objectives View full abstract»

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  • On the suppression of asymmetric artifacts arising in an implementation of the thin-wire method of moments

    Publication Year: 1990 , Page(s): 281 - 285
    Cited by:  Papers (13)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (384 KB)  

    The original version of the thin-wire frequency-domain moment-method program developed by J.H. Richmond (1974) has been modified to suppress the computation of nonphysical asymmetric fields. Richmond's implementation uses piecewise sinusoidal expansion and testing functions, along with filamentary current approximations. The modified version, termed the bridge-current version, is described. The original program and the modified version are compared with each other and with simplified theory, where applicable, on the following symmetrical structures: a rectangular wire loop, a two-wire transmission line, and a log-periodic dipole antenna. The bridge-current version is shown to eliminate the computation of nonphysical asymmetric fields, to be essentially invariant with respect to variations in segmentation for the above-mentioned structures, and to produce results that compare well with simplified theories where applicable. It is noted that the bridge-current version is particularly advantageous for structures that include close-spaced parallel wires connected by short wire segments View full abstract»

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  • The mode features of an annular sector microstrip antenna

    Publication Year: 1990 , Page(s): 265 - 269
    Cited by:  Papers (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (252 KB)  

    A rigorous analysis of the features of the modes of an annular sector printed microstrip antenna is presented. General expressions for its radiation field are derived by using the cavity model. The expressions are used to study the radiation patterns, radiation peak in the broadside direction, and beamwidth of different structures for various sector angles, widths, and modes of excitation. This includes the special cases of quarter-, half-, three-quarters-, and ideal-gap open-ring structures. Compared to a closed ring, the results indicate that the TM12 mode is superior to the TM11 mode with regard to the radiation properties in the annular sector as its angle approaches 2π View full abstract»

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  • Analysis of mutual coupling in finite arrays of different-sized rectangular waveguides

    Publication Year: 1990 , Page(s): 166 - 172
    Cited by:  Papers (41)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (436 KB)  

    A Green's function approach is used to analyze mutual coupling in a finite array of different-sized rectangular waveguides arranged on a rectangular grid. In calculating the self- and mutual admittances for mode coupling, a quadruple integration over the source and observer apertures is involved. Possible means of reducing the order of integration are discussed, with the change of variables approach of L. Lewin (1951) being selected. This approach is generalized to allow coupling between different-sized apertures and leads to derivation of mutual admittance expressions for all possible combinations of transverse electric (TE) and transverse magnetic (TM) mode coupling. Calculations using these expressions are shown to be in good agreement with results published earlier by R.J. Mailloux (1969) and measured data for an antenna comprising a square waveguide and two rectangular waveguides. Coupling between closely spaced different-sized square waveguides is also investigated, and for small apertures minimum coupling is shown to occur when the aperture sidelength is about 1.15 λ View full abstract»

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  • Evaluation of adaptive phased array antenna, far-field nulling performance in the near-field region

    Publication Year: 1990 , Page(s): 173 - 185
    Cited by:  Papers (12)  |  Patents (6)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (760 KB)  

    A theory for analyzing the behavior of adaptive phased array antennas illuminated by a near-field interference test source is presented. Conventional phased array near-field focusing is used to produce an equivalent far-field antenna pattern at a range distance of one to two aperture diameters from the adaptive antenna under test. The antenna is assumed to be a linear array of isotropic receive elements. The interferer is assumed to be a bandlimited noise source radiating from an isotropic antenna. The theory is developed for both partially and fully adaptive arrays. Results are presented for the fully adaptive array case with single and multiple interferers. The results indicate that near-field and far-field adaptive nulling can be equivalent. The adaptive nulling characteristics studied in detail are the array radiation patterns, adaptive cancellation, covariance matrix eigenvalues, and adaptive array weights View full abstract»

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  • The variation of large-angle scattered intensity with the different power laws of the permittivity fluctuation correlation function

    Publication Year: 1990 , Page(s): 289 - 292
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (280 KB)  

    In a recent paper (see D.A. de Wolf and S.R. Begum, J. Opt. Soc. Am. A., vol.2, no.12, p.2106-11, Dec. 1985), explicit results were calculated for a two-dimensional geometry describing cylindrical scattering from a slab of width L filled with a uniformly turbulent dielectric described by the Kolmogorov spectrum. The results show that there is an enhancement in the scattered flux compared to the Born-approximated flux due to the inclusion of cumulative effects of small-angle scatterings. This result is extended in the present work for a generalized power law correlation function of the dielectric permittivity fluctuations. It is shown that the cumulative forward and single large-angle scattered flux is somewhat sensitive to the statistical properties of a random continuum in the inertial subrange View full abstract»

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  • Analysis of arbitrary metallic surfaces conformed to a circular cylinder using the conjugate gradient-fast Fourier transform (CG-FFT) method

    Publication Year: 1990 , Page(s): 286 - 289
    Cited by:  Papers (3)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (248 KB)  

    An efficient scheme for analyzing electrodynamic problems involving arbitrary metallic surfaces conformed to a circular cylinder, using the conjugate-gradient-fast-Fourier-transform (CG-FFT) method, is presented. The numerical method outlined is efficient in CPU time and minimizes the memory storage requirements. Several results are presented and compared with numerical or measured values that appear in the literature View full abstract»

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  • Effects of finite ground plane on the radiation characteristics of a circular patch antenna

    Publication Year: 1990 , Page(s): 152 - 159
    Cited by:  Papers (20)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (528 KB)  

    An analytical technique to determine the effects of finite ground plane on the radiation characteristics of a microstrip antenna is presented. The induced currents on the ground plane and on the upper surface of the patch are determined from the discontinuity of the near field produced by the equivalent magnetic current source on the physical aperture of the patch. The radiated fields contributed by the induced current on the ground plane and the equivalent sources on the physical aperture yield the radiation pattern of the antenna. Radiation patterns of the circular patch with finite ground plane size are computed and compared with the experimental data, and the agreement is found to be good. The radiation pattern, directive gain and input impedance are found to vary widely with the ground plane size View full abstract»

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  • Compound coupling slots for arbitrary excitation of waveguide-fed planar slot arrays

    Publication Year: 1990 , Page(s): 276 - 280
    Cited by:  Papers (19)  |  Patents (1)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (376 KB)  

    A resonant coupling slot cut in the common broad wall of two crossed rectangular waveguides is analyzed. The slot is offset from the center line and tilted with respect to the longitudinal axis of the main waveguide, whereas it is centered-tiled in the branch waveguide. It is shown that the slot offset and tilt control the branch waveguide excitation amplitude with a phase variability of 360°. Pertinent integral equations are developed, taking into account finite wall thickness. The integral equations are solved for the slot aperture electric field using the method of moments. Dominant mode scattering by the slot in both waveguides is obtained View full abstract»

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  • Design of transversely fed EMC microstrip dipole arrays including mutual coupling

    Publication Year: 1990 , Page(s): 145 - 151
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (512 KB)  

    Design techniques and procedures for microstrip dipole arrays transversely fed by proximity coupled microstrip lines are presented. Two design equations which include the effects of mutual coupling are developed, and the corresponding design curves are obtained by a rigorous integral equation solution. A seven-element standing wave linear array is designed to illustrate the developed design procedures. The design data are checked by a complete integral equation solution of the array, with good agreement. The measurements of radiation pattern and input impedance are found to be in good agreement with the design goal View full abstract»

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  • New expressions for mutual impedance of nonplanar-skew sinusoidal monopoles

    Publication Year: 1990 , Page(s): 275 - 276
    Cited by:  Papers (4)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (156 KB)  

    Previously published expressions for monopole-monopole impedance to two nonplanar-skew sinusoidal current filaments are nonreciprocal. A novel version of the monopole-monopole impedance is obtained. This version is not only reciprocal but also contains fewer exponential integral terms. The new expressions can be used to save computer time in the thin wire program developed by J.H. Richmond (1974) View full abstract»

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  • Analysis of arbitrary shape printed line microstrip antennas

    Publication Year: 1990 , Page(s): 269 - 274
    Cited by:  Papers (5)
    Save to Project icon | Request Permissions | Click to expandQuick Abstract | PDF file iconPDF (468 KB)  

    A rigorous solution for arbitrary-shape printed line antennas is developed using the microstrip Green's functions. The current distribution of the line is determined by a moment method and the use of sinusoidal basis functions. Analytical expressions for the far zone fields are obtained using an asymptotic method for evaluating the Sommerfeld integrals. Examples illustrating the accuracy of the method and characteristics of selected printed antennas are presented. It is found that, for undulated printed line elements, the resonance length increases when the undulation height increases. Various examples of undulated printed line elements which are useful for array design are investigated. The effect of the undulation height on the radiation characteristics of the printed line is studied 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