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ABSTRACT: A high-frequency asymptotic technique based on the Uniform Geometric Theory of Diffraction (UTD) is employed for building interior imaging. The analysis is implemented using a ray-tracing technique to account for multiple scattering interactions in a building, along with a set of heuristic diffraction coefficients for dielectric wedges and corners. Imaging of the synthetic aperture radar data is carried out by the conventional fast Fourier transform method to transform to the downrange domain, and combined with a coherent near-zone imaging function for cross-range. Comparisons with experimental data for a scaled-down building model are given to demonstrate the suitability and efficacy of our analysis for through-wall building imaging. The UTD ray mechanisms account for the dominant scattering features observed in the image.
IEEE Transactions on Geoscience and Remote Sensing 06/2009; · 2.89 Impact Factor
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ABSTRACT: Through-wall radar imaging is a challenging area of research due to the complex multi-layer and inhomogeneous structure of building walls. The wall distorts and attenuates the radar signal in a way that is not easy to predict, except in the most simple of cases. In this paper a general periodic model is developed and applied to the imaging algorithm. Periodic dielectric wall models for microwave transmission and reflection have been investigated by several researchers [1-5]. Floquet mode theory [6] is used to find the discrete plane wave directions that are uniquely determined by the period. Below a certain frequency there are no propagating Floquet modes, so only the specularly transmitted and reflected plane waves are present. In this case it is often possible to use an equivalent 3-layer homogeneous model as described in [4]. This makes it much easier to use a ray tracing code such as the NEC-Basic Scattering Code (NEC-BSC) [7] because the Fresnel plane wave reflection and transmission coefficients may be applied directly. Here we compare the 3-layer model with a volume periodic moment method solution. The goal is to generate model-based images using both approaches to see the effect of the periodicity on the image.
Antennas and Propagation Society International Symposium, 2008. AP-S 2008. IEEE; 08/2008
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ABSTRACT: Radar imaging studies of full-scale buildings present serious electromagnetic modeling challenges. The large electrical size makes numerical methods impractical, and the complexity makes ray methods difficult to apply. In this paper we adapt the NEC-basic scattering code (NEC-BSC) [1] to generate simulated radar scattering data for building imaging purposes. The NEC-BSC is based on the uniform geometrical theory of diffraction (UTD) ray tracing method [2,3]. The NEC-BSC combines geometrical optics (GO) ray tracing with the edge and corner diffraction contributions of UTD by constructing models build up of basic canonical shapes, such as plates, cylinders, ellipsoids, cone frustums and wires. For buildings we are primarily interested in models made from multi-layered dielectric plates which represent walls, floors and ceilings. The code traces rays through multiple reflections and diffractions to include the dominant building scattering mechanisms shown in Figure 1, such as dihedrals, trihedrals, direct reflection, and edge and corner diffraction. Higher order combinations of reflections and diffractions are also included, as well as transmission through dielectric plates.
Antennas and Propagation Society International Symposium, 2008. AP-S 2008. IEEE; 08/2008
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ABSTRACT: Through-wall radar imaging has received much attention recently for discerning objects inside of a building. Most conventional imaging approaches are based on Fourier spectral transforms and/or far-field approximations, such as inverse synthetic aperture radar (ISAR) and tomographic imaging. These methods assume a simple point-scattering model. On the other hand, model-based imaging is a more general approach that may utilize a more appropriate scattering model based on the physics of the scenario of interest. In this paper model-based imaging is applied to through-wall imaging with a near-field sensor. The imaging function is presented in a very general form which allows arbitrary sensor movement for collecting the scattering data. A numerical simulation is presented of a drive-by radar scan of a small 1-room building.
Antennas and Propagation Society International Symposium, 2007 IEEE; 07/2007
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ABSTRACT: This paper demonstrates a ray-tracing method for modeling indoor propagation channels at 60 GHz. A validation of the ray-tracing model with our in-house measurement is also presented. Based on the validated model, the multipath channel parameter such as root mean square (RMS) delay spread and the fading statistics at millimeter wave frequencies are easily extracted. As such, the proposed ray-tracing method can provide vital information pertaining to the fading condition in a site-specific indoor environment.
EURASIP Journal on Wireless Communications and Networking. 01/2007;
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ABSTRACT: Hybrid combinations of numerical and asymptotic methods are utilized to evaluate in-situ antenna performance, and coupling to other systems on a shared platform such as a ship topside. This paper describes a combination of the finite element-boundary (FE-BI) method with ray techniques for evaluating antenna patterns in the presence of complex platforms. Specifically, a very complex array antenna may be modeled with FE-BI, and interfaced to the platform via the use of equivalent currents. For the case considered here, the FE-BI is accelerated with the array decomposition fast multipole method (AD-FMM) so that large arrays may be considered. A novel discrete Fourier transform method is also introduced to provide a greatly reduced representation of the fields over a planar array aperture and the uniform theory of diffraction (UTD) along with iterative physical optics (IPO) are used to characterize the platform. To tie it all together, a matrix framework is formulated to iteratively increment the higher order interactions between antennas and platform.
10/2006;
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ABSTRACT: In this paper, an array of closely spaced slot elements has been designed to provide good wide angle scan performance with large bandwidth. The results are stable for a wide range of scan angles and frequencies. The calculated return loss for the design is less than 10 dB for scan angles from 45deg 70deg and for a bandwidth of 40%
Antennas and Propagation Society International Symposium 2006, IEEE; 08/2006
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ABSTRACT: In this paper, based on a 3D ray-tracing analysis, statistical parameters (i.e. mean excess delay and rms delay spread) for site-specific indoor environments were extracted. The fading statistics of these indoor environments were shown to obey a Weibull distribution. As is well-known, fading statistics are necessary for predicting channel capacity limit and this were presented in the conference
Antennas and Propagation Society International Symposium 2006, IEEE; 08/2006
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ABSTRACT: An asymptotic solution based on the uniform geometrical theory of diffraction (UTD) is proposed for the canonical problem of surface field excitation on a circular cylinder with an impedance boundary condition (IBC). The radius of the cylinder and the length of the geodesic path between source and field points, both of which are located on the surface of the cylinder, are assumed to be large compared to a wavelength. Unlike the UTD based solution pertaining to a perfect electrically conducting (PEC) circular cylinder, some higher order terms and derivatives of Fock type integrals are found to be significantly important and included in the proposed solution. The solution is of practical interest in the prediction of electromagnetic compatibility (EMC) and electromagnetic interference (EMI) between conformal slot antennas on a PEC cylindrical structure with a thin material coating on which boundary conditions can be approximated by an IBC. The cylindrical structure could locally model a portion of the fuselage of an aircraft or a spacecraft, or a missile. Validity and accuracy of the numerical results obtained by this solution are demonstrated in comparison with those of an exact eigenfunction solution.
IEEE Transactions on Antennas and Propagation 07/2006; · 2.15 Impact Factor
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ABSTRACT: It is well-known that the high-frequency asymptotic evaluation of surface fields by the conventional geometrical theory of diffraction (GTD) usually becomes less accurate within the paraxial (close to axial) region of a source excited electrically large circular cylinder. Uniform versions of the GTD based solution for the surface field on a source excited perfect electrically conducting (PEC) circular cylinder were published earlier to yield better accuracy within the paraxial region of the cylinder. However, efficient and sufficiently accurate solutions are needed for the surface field within the paraxial region of a source excited circular cylinder with an impedance boundary condition (IBC). In this work, an alternative approximate asymptotic closed form solution is proposed for the accurate representation of the tangential surface magnetic field within the paraxial region of a tangential magnetic current excited circular cylinder with an IBC. Similar to the treatment for the PEC case, Hankel functions are asymptotically approximated by a two-term Debye expansion within the spectral integral representation of the relevant Green's function pertaining to the IBC case. Although one of the two integrals within the spectral representation is evaluated in an exact fashion, the other integral for which an exact analytical evaluation does not appear to be possible is evaluated asymptotically, unlike the PEC case in which both integrals were evaluated analytically in an exact fashion. Validity of the proposed asymptotic solution is investigated by comparison with the exact eigenfunction solution for the surface magnetic field.
IEEE Transactions on Antennas and Propagation 05/2005; · 2.15 Impact Factor
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ABSTRACT: Equivalent circuit representations of frequency selective surfaces (FSS) are useful for quickly predicting the performance of FSS radomes. These equivalent circuit models also provide useful physical insight into the performance of the radome, Two different techniques for obtaining equivalent circuits for lossless FSS have been developed.
Antennas and Propagation Society International Symposium, 2003. IEEE; 07/2003
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ABSTRACT: Spatial averaging is used in conjunction with the normalized data to remove errors in acquiring transmission coefficients from finite material panels. This is illustrated by data obtained from a UTD code, NEC-BSC, and a MM code, ESP. The errors from the scattering from the edges of the panel and scattering between the receiving antenna and the panel are effectively removed with this technique. The minimum size of the panel needed as well as the necessary starting, ending and number of samples points will be discussed.
Antennas and Propagation Society International Symposium, 2003. IEEE; 07/2003
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ABSTRACT: Computation of the exact eigenfunction solution for the surface fields due to a point source on a circular cylinder is usually a very challenging and time consuming task, especially when the radius of the circular cylinder or the geodesic path length between the source and field points is electrically large. An efficient technique is developed for the computation of the exact Green's function pertaining to the surface magnetic field due to a magnetic current on a circular cylinder with an impedance boundary condition (IBC). The results obtained by this technique can be used for the validation and checking of the accuracy of the relevant mutual coupling as well as surface field results obtained by conventional high frequency asymptotic techniques.
Antennas and Propagation Society International Symposium, 2002. IEEE; 02/2002
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ABSTRACT: In order to improve automobile driver safety, manufacturers are exploring a variety of sensing options. A collision avoidance radar is a possible device that provides an all-weather, day-night sensing capability. Systems of various complexities are possible, but they all require an effective antenna system. This paper explores the effects of mounting a small array behind an automobile bumper fascia. This is similar to the standard radome problem. However, the system designer has little input on the make up of the bumper fascia, in terms of thickness, paint, and relative position of antenna and material. Material properties for this study are determined by transmission line measurements for samples of the plastic fascia with and without several different paints. Gain calculations for a patch array in various combinations of bumper configurations are found. The analysis is performed using uniform geometrical theory of diffraction (UTD) techniques. Validation is provided by measurements made in the OSU-ESL compact range.
Antennas and Propagation Society International Symposium, 2002. IEEE; 02/2002
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ABSTRACT: This paper discusses the presence of surface waves on periodic
structures in general and on frequency selective surfaces (FSS) in
particular. While certain types of surface waves can exist on infinite
as well as finite periodic structures, this investigation centers around
the types that can exist only on finite FSS. Radiation caused by these
surface waves may lead to a significant scattering increase in the
backscatter as well as the bistatic directions. Thus, this paper is of
both theoretical and practical interest
IEEE Transactions on Antennas and Propagation 01/2002; · 2.15 Impact Factor
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ABSTRACT: Modem antennas especially arrays are being placed in layers of
materials on complex environments. A rigorous recursive method for plane
wave reflection and transmission coefficients (Richmond, 1965) has been
used in the past for dipoles above multilayer slabs (Aktas et al.,
1998). This solution is modified in this paper to account for forward
and backward traveling rays with appropriate spread factors for a dipole
in the media. Extensive validation for this approximate method shows
good agreement with a method of moments code. This code is developed at
Lawrence Livermore National Laboratory. The geometry for these
comparisons uses a dipole in nontruncated dielectric multilayer slabs
Antennas and Propagation Society International Symposium, 2001. IEEE; 02/2001
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ABSTRACT: An approximate slope diffraction coefficient is developed to improve the approximate UTD solution for the junction between two material plates when the incident angle is close the grazing. The present development has been carried out for plate angles greater than 60° on the source side. However, the method can be extended to angles less than 60° in a similar fashion. The source can be located close to grazing incidence angles when the material is lossy enough to neglect the surface wave. A reasonable improvement over the approximate UTD solution for grazing incidence is obtained with addition of the approximate slope diffraction contribution
Antennas and Propagation Society International Symposium, 1999. IEEE; 09/1999
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ABSTRACT: An approximate uniform geometrical theory of diffraction (UTD)
solution has been developed for the analysis of surface magnetic fields
excited by a magnetic point source on an impedance cylinder. This
solution is useful not only for the analysis of mutual coupling on an
impedance cylinder with a uniform surface impedance or with a surface
impedance patch, but also for the modeling of a thin material coating on
a PEC circular cylinder. Analytically, the proposed UTD solution reduces
to that of a PEC circular cylinder when the surface impedance goes to
zero. This approximate solution compares well also with the
eigenfunction solution, numerically. These comparisons confirm the
validity of the solution
Antennas and Propagation Society International Symposium, 1999. IEEE; 09/1999
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ABSTRACT: The material corner diffraction (CD) solution summarized here has been found to yield very accurate results for the far zone scattering from electrically large material structures made up from flat plates. The solution is presented for an impenetrable, convex material vertex in terms of the perfect electric conductor (PEC) CD coefficients and the reflected components of the geometrical optics (GO) field. The extension to the more general penetrable case is described and numerical results are presented for a penetrable two-plate shell. The solution may be extended to curved surface geometries with tips and corners using the same technique of modifying the PEC diffraction solution via comparison of the PEC and material physical optics (PO) solution
Antennas and Propagation Society International Symposium, 1998. IEEE; 07/1998
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ABSTRACT: An approximate UTD coefficient has been extended for the junction
between two material plates. The present development has been carried
out for plate angles greater than 60° on the source side. However,
the method can be extended to angles less than 60° in a similar
fashion. The source should not be located too close to the surface to
avoid surface waves. Reasonable comparisons between this approximate
solution and moment method solutions are obtained
Antennas and Propagation Society International Symposium, 1998. IEEE; 07/1998
