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ABSTRACT: An efficient and accurate method for the analysis of human backscatter response to ultrawideband near-field UHF radar systems is presented. The method combines a full-wave analysis of a human body model with a PO-like indoor propagation code known as “brick-tracing.” This method allows for the analysis of radar detection and tracking of humans within a realistic building environment. Using this method multi-static radar imaging of a human in buildings is evaluated and certain special features are pointed out. The simulation results are validated with actual radar measurements of a mannequin in a lab environment. A viable method for real time detection and localization of moving human inside buildings is then applied to the simulated and measured data and the building effects on the detection and localization are discussed.
IEEE Transactions on Antennas and Propagation 05/2011; · 2.15 Impact Factor
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ABSTRACT: The detection and tracking of targets in highly cluttered environments often poses a difficult engineering challenge as the strong clutter backscatter contained in the scene makes it difficult to distinguish the target of interest. A design concept to aide in standoff detection and tracking of large metallic objects in a warehouse setting is presented. This includes the design and implementation of an active retro-reflective array system that is able to determine the precise location and identification of an object. To accomplish this, a unique series fed grounded coplanar waveguide patch antenna is designed and implemented with minimal cross coupling among elements. This compact array has a relatively large radar cross-section (RCS) while maintaining the desired retro-reflectivity. Additionally, a tilted beam is incorporated in the linear series-fed array to isolate the large RCS of the planar array structure at boresight from the desired modulated, retro-reflective RCS. This method for enhanced detection is implemented at 26 GHz. The incorporation of the high-speed PIN switches into the array structure provide the tag with a unique identification. Measurement results for the modulated RCS from such an array in a cluttered environment are presented.
IEEE Transactions on Antennas and Propagation 12/2010; · 2.15 Impact Factor
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ABSTRACT: A new technique of phase calibrating the uplink of a ground array consisting of large reflector antennas is studied. The Moon is selected as a calibration target since it falls within the array far-field and avoids the positioning error problem encountered by low-Earth orbit (LEO) calibration targets. As a distributed radar target, the Moon cannot be directly used like point targets. A planetary synthetic aperture radar (SAR) imaging technique is employed to divide the antenna footprint on the lunar surface into many small pixels. Each array element can form its own SAR image of each pixel and the phase differences (interferograms) among these images can be used to perform phase calibration. Orthogonal pseudonoise (PN) codes are used at different array elements to distinguish their signals at a common receiver. A practical design of the calibration system parameters is illustrated. In order to evaluate the performance of this calibration technique, a high-fidelity 3-D lunar surface profile and scattering model is developed. Simulation results are presented to show the effects of multi-pixel averaging, surface undulation, baseline separation, and image misregistration on the proposed calibration performance.
IEEE Transactions on Aerospace and Electronic Systems 11/2010; · 1.10 Impact Factor
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ABSTRACT: A new cavity architecture for applications in design of resonator-backed slot antennas with a height less than λ/15 profile is presented. This architecture renders cavity heights as low as λ/130 and small lateral dimensions. Miniaturization of the supporting cavity resonator is achieved by meandering the passage from the bottom of the cavity resonator to the slot aperture. Unlike conventional cavity resonators, the proposed design operates in a TEM mode which allows for wider bandwidth operation and miniaturization of lateral dimensions. Ultrasonic consolidation technique is employed to fabricate the complicated cavity structure monolithically. Measurements verify the proposed antenna exhibits excellent gain and front-to-back ratio (FTBR). Wide-band mode of the antenna is achieved by using a carefully designed microstrip feed across the slot aperture which facilitates a fictitious short along the slot aperture. The antenna is then flush-mounted onto an arbitrarily built metallic platform and is shown to feature consistent impedance matching. The FTBR is found to improve when the antenna is embedded into the platform. The same antenna architecture is redesigned for VHF band operation using standard multi-layer PCB technology and consistent functionality is verified.
IEEE Transactions on Antennas and Propagation 10/2010; · 2.15 Impact Factor
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ABSTRACT: One of the most fundamental new technical challenges of a DESDynI spaceborne mission is the fusion of the several sensor modalities - LiDAR, SAR, InSAR, and Optical - in order to accurately estimate desired 3D Vegetation structures and biomass parameters at their point of intersection and to extrapolate them over continuous areas. The objective of this paper is to use both our simulation models and measured dataset to develop and validate fusion and extrapolation methods while simulating DESDynl-type missions. We use existing datasets to develop and validate our fusion and extrapolation approach, which involves using our four sensor simulators, including our fractal-based tree geometry generator, in tandem with our in-house parameter estimation software which performs fusion and retrieval functions. We then use existing field and radarlidar-VNIR data for the Boreas southern study area to validate our simulators in this region and construct a large set of boreal trees for use in our fusion and extrapolation processes.
Geoscience and Remote Sensing Symposium (IGARSS), 2010 IEEE International; 08/2010
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ABSTRACT: This article tests the performance of the FSS-antenna array experimentally. A patch-array was fabricated and measured at X-band. The array was then loaded with a frequency-selective layer at a close distance on top. The measured received power as a function of frequency exhibits an improvement of about 50% reduction in the bandwidth and significantly higher frequency roll-off rate once the array is covered with the metamaterial surface.
Antennas and Propagation Society International Symposium (APSURSI), 2010 IEEE; 08/2010
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ABSTRACT: This paper presents a design concept to aid in the detection and tracking of objects in a cluttered environment at 26 GHz. Target tracking can generally be accomplished with the use of retro-reflectors which are able to return an incident signal back in the same direction with a radar cross section (RCS) that is independent of angle of arrival for a large range of incidence angles.
Antennas and Propagation Society International Symposium (APSURSI), 2010 IEEE; 08/2010
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ABSTRACT: This paper presented the concept for an interleaved configuration for a Van Atta retroreflector array for increased beamwidths at broadside. Antenna theory was used to establish a working model to predict the behavior of the entire interconnected array. Agreement is demonstrated between measurement and simulation results for the individual linear arrays along with the entire fabricated retro-reflective structure.
Antennas and Propagation Society International Symposium (APSURSI), 2010 IEEE; 08/2010
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ABSTRACT: A novel, tunable miniaturized-element frequency-selective surface that does not require additional bias networks is presented. This spatial filter is composed of two wire-grids printed on opposite sides of a substrate and connected to each other with an array of varactors using plated via holes. Varactor diodes are positioned between the grids. Via sections and metallic pads are fabricated and create a dc path for biasing the varactors with the grids themselves. This configuration eliminates the need for any additional network, and therefore resolves the design difficulties associated with the spurious response of the bias network. An equivalent circuit model is developed to facilitate the design procedure. Full-wave numerical simulations are used to validate the results based on the circuit model. Simulations show that by altering the capacitance of the varactors from 0.1 to 1 pF, a frequency tunability from 8 to 10 GHz with an almost constant bandwidth can be achieved.
IEEE Transactions on Antennas and Propagation 05/2010; · 2.15 Impact Factor
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ABSTRACT: An investigation on the effects of terrain roughness on near-ground radiowave propagation is featured. In spite of the fact that a variety of analytical and numerical routines have been proposed by many workers for the general treatment of the scattering properties of rough surfaces, much disagreement remains in the solution of the problem for near-grazing scenarios. In striving to analytically describe the near-grazing propagation of signals from 2D and 3D radiators, an existing volumetric polarization current-based perturbation approach is exploited in this work to formulate closed-form expressions for the coherent rough surface reflection coefficients. Although the perturbation approach was originally intended for analyzing the scattering coefficients of a ground with scale of roughness much smaller than the wavelength, it is shown through Monte Carlo simulations that the effective reflection coefficients reported herein are applicable for near-ground path-loss prediction even when the surface variation ( rms height) is on the order of a wavelength or more.
IEEE Transactions on Antennas and Propagation 05/2010; · 2.15 Impact Factor
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ABSTRACT: In this paper, accurate tree stand height retrieval is demonstrated using C-band Shuttle Radar Topography Mission (SRTM) height and ancillary data. The tree height retrieval algorithm is based on modeling uniform tree stands with a single layer of randomly oriented vegetation particles. For such scattering media, the scattering phase center height, as measured by SRTM, is a function of tree height, incidence angle, and the extinction coefficient of the medium. The extinction coefficient for uniform tree stands is calculated as a function of tree height and density using allometric equations and a fractal tree model. The accuracy of the proposed algorithm is demonstrated using SRTM and TOPSAR data for 15 red pine and Austrian pine stands (TOPSAR is an airborne interferometric synthetic aperture radar). The algorithm yields root-mean-square (rms) errors of 2.5-3.6 m, which is a substantial improvement over the 6.8-8.3-m rms errors from the raw SRTM minus National Elevation Dataset Heights.
IEEE Transactions on Geoscience and Remote Sensing 04/2010; · 2.89 Impact Factor
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ABSTRACT: A new filter-antenna array design is presented in this article. This design approach can be employed to simplify the vertical integration of array beamformers. Basically, by placing a high-order filter, whose response is not sensitive to angle of arrival, in front of the array elements, the need for integrating bulky RF filters behind each element is eliminated. A new method for design of such phased-arrays is provided here in which the bandpass filters are removed, and instead, a metamaterial-based frequency-selective surface is placed directly over the antenna to perform the necessary filtering. The small spacing between the frequency-selective surface and the antenna, which is as low as ~ ??/10, results in creation of a compact filter-antenna design. The close proximity of the surface and the antenna is utilized to achieve a proper coupling between the selective surface and the array for high-order filtering without adversely affecting the gain or scan characteristics of the array. To test the performance of this approach, a 9 ?? 9-element patch-array is fabricated and measured at X-band. The array is then loaded with a 0.003"-thick, single-pole frequency-selective layer at a close distance on top. The measured received power as a function of frequency exhibits an improved frequency selectivity (better than the frequency-selective surface or the array alone). An improvement of about 50% reduction in the bandwidth and significantly higher frequency roll-off rate is observed once the array is covered with the metamaterial surface.
IEEE Microwave and Wireless Components Letters 03/2010; · 1.72 Impact Factor
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ABSTRACT: A 2D surface integral equation-based NystrOumlm solver in which a phase extraction technique is utilized to reduce the number of surface unknowns is described. As forward scattering is the dominant mechanism for the near-ground wave propagation scenario, the associated rapidly-varying phase components of the integral equation kernel and solution unknowns are deduced and isolated in advance and subsequently built into the solver. It is shown that by applying this method, when combining with an adaptive surface segmentation routine, as few as one to two average unknowns per wavelength is adequate in obtaining accurate solutions. This significantly reduces the memory storage and computational expense for the simulation of long-distance propagation effects. The efficiency of this method is further improved by incorporating it into the framework of the fast multipole scheme. The full details of the algorithm are discussed, along with performance comparisons of the new solver to a regular NystrOumlm solver for terrain surfaces in terms of solution convergence.
IEEE Transactions on Antennas and Propagation 01/2010; · 2.15 Impact Factor
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ABSTRACT: The objective of this research is to demonstrate the efficacy of using acoustic and electromagnetic (acousto-EM) wave interaction and time-reversal focusing in the non-destructive evaluation of an object. Acousto-EM wave interaction occurs when an electromagnetic wave scatters from an object under seismic or acoustic illumination; the acoustic vibration of the object gives rise to a frequency modulated scattered electromagnetic field which is a function of the object and both the electromagnetic and acoustic source parameters. A recently developed model, which is capable of predicting the first Doppler component of the frequency modulated scattered field for arbitrary two-dimensional objects over a wide bandwidth, is used in the analysis. Time reversal focusing is also used to improve sensitivity and obtain information about the location of flaws within the target. Both the unshifted electromagnetic fields scattered from the stationary target and the Doppler component are analyzed. The sensitivity of the Doppler component to the presence of flaws, which perturb the mechanical mode shape and resonance frequency, is demonstrated for application in non-destructive evaluation.
IEEE Transactions on Antennas and Propagation 12/2009; · 2.15 Impact Factor
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ABSTRACT: The horizontal and vertical (3D) structure of Earth's forested ecosystems are of great significance to their ecological functioning and societal uses. An InSAR approach is one methodology whereby a forest's structure and height in particular can be successfully estimated. Critical to the successful estimation is a high correlation between multiple SAR images. Regardless of a forest's location on the Earth, wind can significantly alter a forest's appearance to an L-band SAR system and so decrease this necessary correlation. In order to investigate the wind-induced decorrelation, we have developed a model for the repeat-pass interferometric SAR response of a forested area taking into account wind effects. The simulation consists of multiple interconnected parts including static tree geometry's generation, a wind simulator to apply to a static tree, and an electromagnetic model to allow us to calculate the interferometric SAR response. The static tree geometry generation process generates a pseudo-random tree based on a given DNA file which specifies a species specific structure. This geometry is then modified by the wind simulator producing snapshots of tree-geometry as a function of time. Each snapshot is then used in the interferometric SAR simulator to synthesize the wind-blown geometry's InSAR response. Results present coherence as a function of wind speed and forest structure. An important feature of this research is the usage of a physically based realistic wind model that is based on measurements of wind effects on trees as well as realistic models of fluid flow and simple harmonic branch resonators. Allowing branches to bend and move out of the plane of the incident wind field enables our model to capture numerous features of a physical tree blowing in the wind. This realistic model is necessary for a realistic simulation of the effects that wind has on a given InSAR imaging system.
Geoscience and Remote Sensing Symposium,2009 IEEE International,IGARSS 2009; 08/2009
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ABSTRACT: A semi-analytic model for near-earth wave propagation in the presence of building walls or similar obstacles is devised. The method is based on physical optics type approximations used in conjunction with the volume equivalence principle. Norton surface waves that are typically neglected in more common indoor propagation techniques such as ray tracing are included in this method as they prove to be vital for the accurate prediction of fields especially for sources close to ground. Simulation results have shown that, this method gives much more accurate results than ray tracing and proves to be computationally better than a numerical method and hence could be used to analyze field propagation in indoor structures that are large in terms of wavelength.
Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009
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ABSTRACT: In this paper, we presented a compact directive UWB transmit receive antenna pair. The basic operation of the antenna was discussed and the effect of the dimensions on the bandwidth, pattern and isolation performance was investigated. The antenna was fabricated and measured. The measurement and simulation results showed good agreement. The measured isolation was better than 21 dB and the measured VSWR was better than 2.3 over the band 0.9-3 GHz.
Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009
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ABSTRACT: A unique design of series-fed grounded coplanar waveguide (GCPW) patch arrays for use in retro-reflective arrays is presented. For the current application, a planar retro-reflector which is capable of providing large radar cross-section (RCS) and signal modulation, and can also operate on metallic surfaces from 25.5-26.5GHz is desired. Linear, series-fed GCPW patch arrays are employed as the radiating elements. Using constituent arrays allows maximization of RCS using the minimum number of active components. Additionally, the unique orientation of the series-fed arrays provides beam squinting, allowing for ease of target identification and distinguishing the response from that of the array ground plane. The array design and results are briefly presented herein. Integration of the array in the intended system application is discussed in a separate conference submission.
Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009
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ABSTRACT: This paper presents a design concept to aid in the detection and tracking of objects in a cluttered environment. The goal is to uniquely identify large, relatively cylindrical metallic objects in a warehouse setting. In addition to the challenge of determining the object's precise location, it is also desirable to uniquely identify each cylinder. The application is similar to RFID but differs in that much longer range of operation is needed and operation on metallic objects is required. A planar Van Atta retro-reflector is used as the baseline for the RF tag with large angle-independent radar cross-section.
Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009
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ABSTRACT: A hybrid simulation of wideband polarimetric radar backscatter of humans within a building is introduced. The model is composed of a full-wave simulation tool that can accurately predict the scattering from a realistic human model, and an accurate indoor wave propagation and scattering model, known as bricktracer. These two models are efficiently connected using a Huygen's interface box that encloses the entire human body. Sample backscattering results for a human walking in a small building were presented. It was shown that the backscatter response of human can be completely obscured by the building backscatter clutter. Time-sequenced subtraction of the backscattered responses using a stationary transceiver was proposed to detect a mover. This method can be used for the development and testing of highly sophisticated location and detection algorithms of humans inside building.
Antennas and Propagation Society International Symposium, 2009. APSURSI '09. IEEE; 07/2009
