Caner Ozdemir

A Study on Millimeter-Wave Imaging of Concealed Objects: Application Using Back-Projection Algorithm

Millimeter-wave (MMW) imaging is a powerful tool for the detection of objects concealed under clothing. Several factors including difierent kinds of objects, variety of covering materials and their thickness, accurate imaging of near-fleld scattered data afiect the success of detection. To practice with such considerations, this paper presents the two-dimensional (2D) images of difierent targets hidden under various fabric sheets. The W-band inverse synthetic aperture radar (ISAR) data of various target-covering situations are acquired and imaged by applying both the focusing operator based inversion algorithm and the spherical back-projection algorithm. Results of these algorithms are demonstrated and compared to each other to assess the performance of the MMW imaging in detecting the concealed objects of both metallic and dielectric types.

PRACTICAL ALGORITHMS TO FOCUS B-SCAN GPR IMAGES: THEORY AND APPLICATION TO REAL DATA

It is well known in B-scan ground penetrating radar (GPR) imagery that the underground scatterers generally exhibit defocused, hyperbolic characteristics. This is mainly due to the data collection scheme and the finite beam width of the main lobe of the GPR antenna. To invert this undesirable effect and obtain focused images, various migration or focusing algorithms have been developed. In this paper, we survey the performance of our recent focusing algorithms, namely; hyperbolic summation (HS) and frequency-wavenumber (w-k) based synthetic aperture radar (SAR) focusing. The practical usage of these focusing methods were tested and examined on both simulated and measured GPR data of various buried targets. The simulation data set is obtained by a physical optics shooting and bouncing ray (PO-SBR) technique code. Measurements were taken by a stepped frequency continuous wave (SFCW) radar set-up. Scattered C-band field data were measured from a laboratory sand box and from outdoor soil environment. The proposed focusing methods were then applied to the B-scan GPR images to enhance the resolution quality within these images. The resultant GPR images obtained with the proposed algorithms demonstrate enhanced lateral resolutions.

ASAR-antenna synthetic aperture radar imaging

The antenna synthetic aperture radar (ASAR) imaging concept is introduced. We present the ASAR imaging algorithm to pinpoint the locations of secondary scattering off a platform from antenna radiation data. It is shown that a three-dimensional (3-D) ASAR image of the platform can be formed by inverse Fourier transforming the multifrequency, multiaspect far-field radiation data from an antenna mounted on the platform. This concept is demonstrated using the computed radiation data from the code Apatch, which employs the shooting and bouncing ray (SBR) technique. Furthermore, we develop a fast ASAR algorithm specially tailored for the SBR approach. By taking advantage of the ray tracing information within the SBR engine, we demonstrate that the fast approach can result in the same quality of image as the frequency-aspect algorithm at only a fraction of the computation time.

Joint time-frequency interpretation of scattering phenomenology in dielectric-coated wires

The scattering phenomenology in dielectric-coated wire structure is investigated using the joint time-frequency processing of simulated and measurement data. The method of moments is applied to carry out the simulation. The computed results are compared to measured data in both the frequency and time domains. The scattering data are next analyzed in the joint time-frequency plane by using the short-time Fourier transform (STFT) technique to provide further insight into the scattering phenomenology. The dispersive Goubau mode excited along the coated wire can be clearly observed in the joint time-frequency plane. In addition, the time-frequency distribution series, which improves the resolution of the STFT while overcoming the cross-term interference problem of the Wigner-Ville distribution, is applied to better identify backscattering returns that are difficult to resolve in the joint time-frequency plane.

A Review on Migration Methods in B-Scan Ground Penetrating Radar Imaging

Even though ground penetrating radar has been well studied and applied by many researchers for the last couple of decades, the focusing problem in the measured GPR images is still a challenging task. Although there are many methods offered by different scientists, there is not any complete migration/focusing method that works perfectly for all scenarios. This paper reviews the popular migration methods of the B-scan GPR imaging that have been widely accepted and applied by various researchers. The brief formulation and the algorithm steps for the hyperbolic summation, the Kirchhoff migration, the back-projection focusing, the phase-shift migration, and the - migration are presented. The main aim of the paper is to evaluate and compare the migration algorithms over different focusing methods such that the reader can decide which algorithm to use for a particular application of GPR. Both the simulated and the measured examples that are used for the performance comparison of the presented algorithms are provided. Other emerging migration methods are also pointed out.

A radiation center representation of antenna radiation patterns on a complex platform

A sparse model of the antenna radiation pattern on a complex platform is presented. This representation is based on a point radiator model that describes the radiation pattern by a collection of radiation centers on the platform. The methodology for obtaining the radiation center model is presented. It entails first generating the three-dimensional (3-D) antenna synthetic aperture radar (ASAR) imagery of the platform and then parameterizing the resulting image by a collection of point radiators via the CLEAN algorithm. It is shown that once such a representation is obtained, we can reconstruct and extrapolate antenna radiation patterns over frequencies and aspects with good fidelity, thus achieving high data compression ratio. Furthermore, it is shown that the resulting radiation center information can be used to pinpoint cause-and-effect in platform scattering and provide important guidelines for reducing platform effects.

A novel localization technique for wireless sensor networks using adaptive antenna arrays

In this work, we introduce a novel location estimation technique which uses adaptive antenna arrays (AAA) at the central node in wireless sensor networks (WSN). This localization technique can be used at the setup phase in the routing protocol. This technique is based on scanning the desired region in azimuth and radial directions by changing parameters of downlink beam. This sweeping process can activate the nodes in the desired region which is specified by beamwidth and beamdirection of the transmit beam and also by minimum and maximum thresholds (Rmin and Rmax) for the received signal strength indicator (RSSI). Active nodes in the desired region transmit their IDs and RSSI levels via multi hop communication to the central node. Unlike GPS-based or beacon based localization techniques, the proposed technique does not require any modification in the sensor nodes. The accuracy of location estimation depends on beam direction, beamwidth and transmit power for downlink beams. The results show that by carefully adjusting these parameters, desired performance can be achieved.

A Review of Recent Patents on Ultra Wide Band (UWB) Antennas

In this article, recent patents on UWB antennas are reviewed; different geometries, design parameters and their experimental results are discussed. Several types of UWB antennas including special horn, patch and array antennas in recent patents are explained together while comparing their measured return loss, gain and radiation patterns. Projections to the future developments of UWB antenna technology are also given.

ACSAR-Antenna Coupling Synthetic Aperture Radar Imaging Algorithm

A synthetic aperture radar imaging technique called ACSAR for antenna coupling scenarios is introduced. It is shown that an ACSAR image of a platform can be formed by inverse-Fourier transforming the multi-frequency, multi-spatial coupling data between two antennas. Furthermore, we present a fast ACSAR imaging algorithm that is specifically tailored to the shooting and bouncing ray (SBR) technique. The fast algorithm is shown to reduce the total simulation time by several orders of magnitude without significant loss of fidelity. Finally, a sparse representation of ACSAR imagery is introduced by extracting the point radiators in the image. By parameterizing the ACSAR image, it is possible to reconstruct the 3-D ACSAR image and the 3-D frequency-spatial data with a very sparse set of radiation centers.

Fast ASAR image formation using the shooting and bouncing ray technique

We have recently devised a diagnostic algorithm for imaging antenna-platform interactions from antenna radiation data. The algorithm, termed ASAR (antenna synthetic aperture radar) imaging, utilizes multi-frequency, multi-aspect radiation data and Fourier processing to create a 3D map of the platform showing the locations of dominant secondary radiation on the platform. Such an algorithm can be used to process either measurement data or computed data from electromagnetic solvers. In this paper, we consider the case when the SBR (shooting and bouncing ray) approach is used to simulate the antenna radiation data. It is shown that a fast ASAR imaging algorithm especially tailored for the SBR approach can be derived. By taking advantage of the ray tracing information within the SBR engine, we will show that the ASAR image can be generated directly in the image domain without resorting to any multiple frequency-aspect calculations. Such an idea is similar to the image-domain ISAR formation process we have reported previously (1995). Furthermore, we can apply an FFT-based algorithm to speed up the ASAR image formation time. Using such a fast approach, it is possible to obtain the same quality of ASAR image as frequency-aspect approach at only a fraction of the computation time (minutes versus hours).