Alexander Yarovoy

A Sparse Aperture MIMO-SAR-Based UWB Imaging System for Concealed Weapon Detection

A high-resolution imaging system based on the combination of ultrawideband (UWB) transmission, multiple-input-multiple-output (MIMO) array, and synthetic aperture radar (SAR) is suggested and studied. Starting from the resolution requirements, spatial sampling criteria for nonmonochromatic waves are investigated. Exploring the decisive influence of the systems fractional bandwidth (instead of previously claimed aperture sparsity) on the imaging capabilities of sparse aperture arrays, a MIMO linear array is designed based on the principle of effective aperture. For the antenna array, an optimized UWB antenna is designed allowing for distortionless impulse radiation with more than 150% fractional bandwidth. By combining the digital beamforming in the MIMO array with the SAR in the orthogonal direction, a high-resolution 3-D volumetric imaging system with a significantly reduced number of antenna elements is proposed. The proposed imaging system is experimentally verified against the conventional 2-D SAR under different conditions, including a typical concealed-weapon-detection scenario. The imaging results confirm the correctness of the proposed system design and show a strong potential of the MIMO-SAR-based UWB system for security applications.

UWB Array-Based Sensor for Near-Field Imaging

In this paper, the development of an ultra-wideband (UWB) array-based time-domain radar sensor for near-field imaging is described. The radar sensor is designed to be used within a vehicle-mounted multisensor system for humanitarian demining. The main novelty of the radar lies in the system design with a single transmitter and multichannel receiver. Design of the UWB antenna array is also novel. The radar produces 3D images of subsurface by 1D mechanical scanning. The imaging capability of the radar is realized via electronic steering of the receive antenna footprint in a cross-scan direction and synthetic aperture processing in an along-scan direction. Imaging via footprint steering allows for a drastic increase in the scanning speed.

Signal Processing for Improved Detection of Trapped Victims Using UWB Radar

Detection of trapped victims using ultrawideband radar is considered a highly challenging task due to multiple unknown parameters and generally very low signal-to-noise-and-clutter ratio (SNCR) conditions. In this paper, we propose a novel detection algorithm which is designed for detection of periodic motion caused by, e.g., respiratory motion of the victim for low SNCR conditions. The aim is to separate the respiratory-motion response of a trapped victim from nonstationary clutter originating from moving objects in the scene of interest. The algorithm performs stationary-clutter removal, high-level noise, and nonstationary-clutter suppression, indicates presence of the trapped victim, and estimates its range. The performance of the algorithm is investigated, both by means of simulation and experimental verification. The results show improved detection capabilities in low SNCR over an existing algorithm proposed by Zaikov et al.

Compressive Stepped-Frequency Continuous-Wave Ground-Penetrating Radar

Data acquisition speed is an inherent problem of stepped-frequency continuous-wave (SFCW) radars, which may discourage further usage and development of this technology. We propose an emerging paradigm called compressed sensing (CS) to overcome this problem. In CS, a signal can be reconstructed exactly based on only a few samples below the Nyquist rate. Accordingly, the data acquisition speed can be increased significantly. A novel design of an SFCW ground-penetrating radar (GPR) with high acquisition speed is proposed and evaluated. Simulation by a monocycle waveform and actual measurement by a vector network analyzer at a GPR test range indicate the applicability of the proposed system.

Modified Kirchhoff Migration for UWB MIMO Array-Based Radar Imaging

In this paper, the formulation of Kirchhoff migration is modified for multiple-input-multiple-output (MIMO) array-based radar imaging in both free-space and subsurface scenarios. By applying the Kirchhoff integral to the multistatic data acquisition, the integral expression for the MIMO imaging is explicitly derived. Inclusion of the Snells law and the Fresnels equations into the integral formulation further expends the migration technique to subsurface imaging. A modification of the technique for strongly offset targets is proposed as well. The developed migration techniques are able to perform imaging with arbitrary MIMO configurations, which allow further exploration of the benefits of various array topologies. The proposed algorithms are compared with conventional diffraction stack migration on free-space synthetic data and experimentally validated by ground-penetrating radar experiments in subsurface scenarios. The results show that the modified Kirchhoff migration is superior over the conventional diffraction stack migration in the aspects of resolution, side-lobe level, clutter rejection ratio, and the ability to reconstruct shapes of distributed targets.

Codesign of an impulse generator and miniaturized antennas for IR-UWB

The codesign of an impulse generator and miniaturized antennas for ultra-wideband impulse radio is described. The impulse generator, discussed by Bragga in 2004, is designed with differential outputs that are fed to the antenna, producing an optimum match of the generator to the antenna, an improved magnitude response, and reduced ringing of the radiated pulse. The impulse generator is preceded by a programmable pulse-position modulator and consists of a triangular pulse generator and a cascade of complex first-order systems, which, in turn, are made up of differential pairs employing partial positive feedback to approximate a Gaussian monocycle waveform. The complete pulse generator is fabricated in IBM 0.18-/spl mu/m Bi-CMOS IC technology. Measurements show the correct operation of the circuit for supply voltages of 1.8 V and a power consumption of 45 mW. The output pulse approximates the Gaussian monocycle having a pulse duration of about 375 ps. Proper modulation of the pulse in time is confirmed. A number of antennas with differentially fed baluns and input impedances of 100 /spl Omega/ have been designed. From measurements, it can be seen that ringing is considerably smaller as compared to conventionally fed antennas.

Polarimetric Video Impulse Radar for Landmine Detection

A full-polarimetric ultra wideband GPR front-end has been developed. The technical specifications of the radar have been determined based on the analysis of different GPR scenarios and based on “user-oriented” demands. The radar has been designed to meet most of these specifications and at the same time to be within a limited budget. The front-end comprises a generator section, a multi-static antenna system and a receiving unit based on a multi-channel sampling converter. The novelty aspects of the radar are: principally new antenna system, use of multiple pulse generators and compensation circuits to improve stability of the system. In comparison with commercially available video impulse GPR systems the key advantages of the front-end are the considerably larger bandwidth, the ability to measure the polarimetric structure of the scattered field and the high precision of scattered field measurements. The front-end is suitable for subsurface imaging with 3D resolution sufficient for antipersonnel mine detection and recognition.

UWB radar for human being detection

UWB radar for detection and positioning of human beings in complex environment has been developed and manufactured. Novelty of the radar lies in its large operational bandwidth (11.7 GHz at -10 dB level) combined with high time stability. Detection of respiratory movement of a person in laboratory conditions has been demonstrated. Based on experimental results human being radar return has been analysed in the frequency band from 1 GHz until 12 GHz. Novel principle of human being detection is considered and verified experimentally

Data Processing and Imaging in GPR System Dedicated for Landmine Detection

Improvements of GPR technology can be attained by making adjustments specific for the application of landmine detection on three levels: system design, data acquisition and data processing. In this paper we describe data processing algorithms specially developed for a novel video impulse ultra-wide band front end. With this front end, three-dimensional measurements (C-scans) have been carried out over a controlled test site, using a non-metallic scanner. The test site contained surface-laid and shallow buried landmines, both antitank and antipersonnel, made of plastic, wood, and metal. Because of practical limitations, the data have been acquired on an irregular grid. We have designed data preprocessing and imaging algorithms such that they take into account the specific antenna geometry and its elevation above the ground as well as the irregularity of the data acquisition grid. We show that by tuning the data pre-processing and imaging to the newly designed radar front end and to the particular data acquisition strategy, we obtain clear subsurface images. The resulting images show the ability of the GPR system to detect and visualize small surface laid and shallow buried targets.

Three-Dimensional Near-Field MIMO Array Imaging Using Range Migration Techniques

This paper presents a 3-D near-field imaging algorithm that is formulated for 2-D wideband multiple-input-multiple-output (MIMO) imaging array topology. The proposed MIMO range migration technique performs the image reconstruction procedure in the frequency-wavenumber domain. The algorithm is able to completely compensate the curvature of the wavefront in the near-field through a specifically defined interpolation process and provides extremely high computational efficiency by the application of the fast Fourier transform. The implementation aspects of the algorithm and the sampling criteria of a MIMO aperture are discussed. The image reconstruction performance and computational efficiency of the algorithm are demonstrated both with numerical simulations and measurements using 2-D MIMO arrays. Real-time 3-D near-field imaging can be achieved with a real-aperture array by applying the proposed MIMO range migration techniques.