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307
Polarimetric scattering and emission properties of targets with reflection symmetry
 Radio Sci
, 1994
"... Abstract. This paper investigates the symmetry of polarimetric scattering and emission coefficients of media with reflection symmetry. A reflection operator is defined and is used to create the images of electromagnetic fields and sources. The image fields satisfy Maxwell's equations, meaning t ..."
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Abstract. This paper investigates the symmetry of polarimetric scattering and emission coefficients of media with reflection symmetry. A reflection operator is defined and is used to create the images of electromagnetic fields and sources. The image fields satisfy Maxwell's equations, meaning that Maxwell's equations are invariant under the described reflection operations. By applying the reflection operations to media with reflection symmetry, the symmetry properties of the Stokes parameters, characterizing the polarization state of thermal emissions, are shown to agree with existing experimental data. The first two Stokes parameters are symmetric with respect to the reflection plane, while the third and fourth Stokes parameters have odd symmetry. In active remote sensing, the symmetry properties of the polarimetric scattering matrix elements of deterministic targets and the polarimetric covariance matrix elements of random media or distributed targets are examined. For deterministic targets, the crosspolarized responses are odd functions with respect to the symmetry direction, whereas the copolarized responses are even functions. For distributed targets or random media, it is found that the correlations of copolarized and crosspolarized responses are antisymmetric with respect to the reflection plane, while the other covariance matrix elements are symmetric. Consequently, in the cases of backscatter, the copolarized and crosspolarized components are completely uncorrelated when the incidence direction is on the symmetry plane. The derived symmetry properties of polarimetric backscattering coefficients agree with the predictions of a twoscale surface scattering model and existing sea surface HH and VV backscatter data. Finally, the conditions for a general type of media, i.e., bianisotropic media, to be reflection symmetric are examined. 1.
Monte Carlo Simulation of Electromagnetic Scattering from TwoDimensional Random Rough Surfaces
 IEEE Trans. Antennas Propagat
, 1997
"... The fast multipole methodfast Fourier transform (FMMFFT) method is developed to compute the scattering of an electromagnetic wave from a twodimensional rough surface. The resulting algorithm computes a matrixvector multiply in O(NlogN) operations. This algorithm is shown to be more efficient than ..."
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The fast multipole methodfast Fourier transform (FMMFFT) method is developed to compute the scattering of an electromagnetic wave from a twodimensional rough surface. The resulting algorithm computes a matrixvector multiply in O(NlogN) operations. This algorithm is shown to be more efficient than another O(NlogN) algorithm, the multilevel fast multipole algorithm (MLFMA), for surfaces of small height. For surfaces with larger roughness, the MLFMA is found to be more efficient. Using the MLFMA, Monte Carlo simulations are carried out to compute the statistical properties of the electromagnetic scattering from twodimensional random rough surfaces using a workstation. For the rougher surface, backscattering enhancement is clearly observable as a pronounced peak, in the backscattering direction, of the computed bistatic scattering coefficient. For the smoother surface, the Monte Carlo results compare well with the results of the approximate Kirchhoff theory. y This work was supported ...
A new shapebased method for object localization and characterization from scattered data
 IEEE Trans. Geosci. Remote Sensing
, 2000
"... The problem of characterizing the structure of an object buried in an inhomogeneous halfspace of unknown composition is considered. We develop a nonlinear inverse scattering algorithm based on a low dimensional parameterization of the unknown object and the background. In particular, we use low or ..."
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The problem of characterizing the structure of an object buried in an inhomogeneous halfspace of unknown composition is considered. We develop a nonlinear inverse scattering algorithm based on a low dimensional parameterization of the unknown object and the background. In particular, we use low order polynomials to represent the contrast in the real and imaginary parts of the object and background complex permittivities. The boundary separating the target from the unknown background is described using a periodic, quadratic Bspline curve whose control points can be individually manipulated. We determine the unknown control point locations and contrast expansion coecients using a greedytype approach to minimize a regularized leastsquares cost function. The regularizer used here is designed to constrain the geometric structure of the boundary of the object and is closely related to snake methods employed in the image processing community. We demonstrate the performance of our approach via extensive numerical simulation involving 2D, TM z scattering geometries.
Quality factor of an electrically small antenna radiating close to a conducting plane
 IEEE Trans. Antennas Propagat
, 2001
"... Abstract—Expressions are derived for the smallest achievable radiation quality factor ( ) of an electrically small antenna in front of a conducting plane. Applying the lowfrequency approximation to the source region involving an electric or a magnetic point dipole plus their images behind the plane ..."
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Abstract—Expressions are derived for the smallest achievable radiation quality factor ( ) of an electrically small antenna in front of a conducting plane. Applying the lowfrequency approximation to the source region involving an electric or a magnetic point dipole plus their images behind the plane, an expression is formed for the field in the radiation zone. The contribution of nonpropagating energy in the near field is obtained explicitly using a spherical harmonics decomposition. The radiation is found to depend on the radius (relative to wavelength) of the smallest sphere that encloses the antenna and its image, the ratio of the vertical and horizontal dipole moments, as well as the positions of the dipoles relative to each other and to the plane. A number of simple wire structures are analysed with NEC (based on the Method of Moments), and the approximate obtained from their fractional bandwidth are compared to the corresponding theoretical minima. Index Terms—Electrically small antennas, ground plane, Q factor. I.
Simovski, “Dynamic model of artificial reactive impedance surfaces
 J. of Electromagn. Waves and Appl
, 2003
"... AbstractNew arti cial reactive impedance surfaces have been recently suggested by Sievenpiper et al. for antenna and waveguide applications. In particular, high impedance values corresponding to a magnetic wall can be realized in dense arrays of conducting patches over a conducting plane. In this ..."
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AbstractNew arti cial reactive impedance surfaces have been recently suggested by Sievenpiper et al. for antenna and waveguide applications. In particular, high impedance values corresponding to a magnetic wall can be realized in dense arrays of conducting patches over a conducting plane. In this paper, a dynamic model for the electromagnetic properties of such structures is developed. The analytical model takes into account electromagnetic interactions between all patches in in nite arrays excited by normally incident plane waves, as well as higherorder Floquet modes between the array and the ground plane. The results are compared with the known experiments.
Some reflections on double negative materials
 Progress In Electromagnetics Research, PIER
, 2005
"... We study the energy conservation property and loss condition of a lefthanded material (LHM). First we argue by energy conservation that an LHM has to be a backwardwave material (BWM). Then we derive the equivalence of the loss and the Sommerfeld farfield radiation conditions for BWM. Next, we sol ..."
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We study the energy conservation property and loss condition of a lefthanded material (LHM). First we argue by energy conservation that an LHM has to be a backwardwave material (BWM). Then we derive the equivalence of the loss and the Sommerfeld farfield radiation conditions for BWM. Next, we solve the realistic Sommerfeld problem of a point source over an LHM half space and an LHM slab. With this solution, we elucidate the physics of the interaction of a point source with an LHM half space and an LHM slab. We interprete our observation with surface plasmon resonance at the interfaces as well as the resonance tunneling phenomenon. This analysis lends physical insight into the interaction of a point source field with an LHM showing that superresolution beyond the diffraction limit is possible with a very low loss LHM slab. 1
Cloaking a perfectly conducting sphere with rotationally uniaxial nihility media in monostatic radar system
 Progress In Electromagnetics Research
"... Abstract—In this paper, the backscattering properties of a perfect electric conducting sphere coated with layered anisotropic media whose constitutive parameters are close to nihility are investigated. We show that the backscattering is more sensitive to the radial constitutive parameters than to th ..."
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Abstract—In this paper, the backscattering properties of a perfect electric conducting sphere coated with layered anisotropic media whose constitutive parameters are close to nihility are investigated. We show that the backscattering is more sensitive to the radial constitutive parameters than to the tangential ones. Compared with isotropic case, the anisotropic media with small axial parameters have the potential to yield more reduction of backscattering magnitude on coated perfectly conducting spheres. 1.
Superdirectivity in MIMO systems
 IEEE Trans. Antennas Propagat
, 2005
"... Abstract—Multiantenna systems such as devices for multipleinput–multipleoutput (MIMO) communication can theoretically use array superdirectivity to optimally exploit the propagation channel. In traditional analyses of MIMO systems, such superdirectivity is not observed due to the commonly applie ..."
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Abstract—Multiantenna systems such as devices for multipleinput–multipleoutput (MIMO) communication can theoretically use array superdirectivity to optimally exploit the propagation channel. In traditional analyses of MIMO systems, such superdirectivity is not observed due to the commonly applied constraint that limits the excitation current magnitudes. However, when an electromagnetically appropriate constraint on the power radiated by the array is applied, the computed capacity can include effects of transmit superdirectivity. A similar result occurs at the receiver for spatially colored noise. This paper formulates the MIMO system capacity under these circumstances and provides a framework for computing this capacity when the level of tolerable superdirectivity (as measured by the superdirectivity factor) is constrained. Example computations using the framework illustrate the impact that superdirectivity can have on achievable
Microwave backscatter modeling of erg surfaces in the sahara desert
 IEEE Transactions on Geoscience and Remote Sensing
, 2005
"... Abstract—The Sahara desert includes large expanses of sand dunes called ergs. These dunes are formed and constantly reshaped by prevailing winds. Previous study shows that Saharan ergs exhibit significant radar backscatter ( ) modulation with azimuth angle (). We use measurements observed at various ..."
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Abstract—The Sahara desert includes large expanses of sand dunes called ergs. These dunes are formed and constantly reshaped by prevailing winds. Previous study shows that Saharan ergs exhibit significant radar backscatter ( ) modulation with azimuth angle (). We use measurements observed at various incidence angles and from the NASA Scatterometer (NSCAT), the SeaWinds scatterometer, the ERS scatterometer (ESCAT), and the Tropical Rainfall Measuring Mission’s Precipitation Radar to model the response from sand dunes. Observations reveal a characteristic relationship between the backscatter modulation and the dune type, i.e., the number and orientation of the dune slopes. Sand dunes are modeled as a composite of tilted rough facets, which are characterized by a probability distribution of tilt with a mean value, and small ripples on the facet surface. The small ripples are modeled as cosinusoidal surface waves that contribute to the return signal at Bragg angles only. Longitudinal and transverse dunes are modeled with rough facets having Gaussian tilt distributions. The model results in a response similar to NSCAT and ESCAT observations over areas of known dune types in the Sahara. The response is high at look angles equal to the mean tilts of the rough facets and is lower elsewhere. This analysis provides a unique insight into scattering by largescale sand bedforms. Index Terms—Backscatter, erg, ERS Scatterometer (ESCAT),
Relativistic electrodynamics: various postulates and ratiocinations”, PIER—Progress
 In Electromagnetic Research
, 2005
"... Abstract—Presently various models consistent with Einstein’s Special Relativity theory are explored. Some of these models have been introduced previously, but additional models are possible, as shown here. The topsyturvy model changes the order of postulates and conclusions of Einstein’s original t ..."
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Abstract—Presently various models consistent with Einstein’s Special Relativity theory are explored. Some of these models have been introduced previously, but additional models are possible, as shown here. The topsyturvy model changes the order of postulates and conclusions of Einstein’s original theory. Another model is given in the spectral domain, with the relativistic Doppler Effect formulas replacing the Lorentz transformation. In this model a new principle tantamount to the constancy of the speed of light in vacuum is stated and analyzed, dubbed as the constancy of light slowness in vacuum. Because the slowness is derived in the spectral domain from the Doppler Effect formulas, this result is not trivially semantic. It is shown that potentials and equations of continuity can replace the Maxwell Equations used by Einstein for his “Principle of Relativity” in electrodynamics. It is also shown that defining convection currents and assuming the currentcharge densities transformations can replace