Xiaodong Zhuge

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.

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.

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.

UWB array-based radar imaging using modified Kirchhoff migration

This paper presents a new modification of Kirchhoff migration algorithm for ultra-wideband (UWB) array-based radar imaging. The developed algorithm is evolved from traditional Kirchhoff migration which is based on the classical integral theorem of Helmholtz and Kirchhoff. The new algorithm is designed for array-based radar imaging with arbitrary multiple input multiple output (MIMO) configuration. The developed algorithm is compared with conventional diffraction stack migration using both synthetic data from numerical simulation and measurement data from landmine detection. The results have shown promising improvements in the aspects of beamwidth, side-lobe rejection ratio and the ability to reconstruct shapes of distributed targets.

Study on Two-Dimensional Sparse MIMO UWB Arrays for High Resolution Near-Field Imaging

A novel generic topology for two-dimensional (2-D) sparse multiple-input-multiple-output (MIMO) ultrawideband (UWB) arrays is suggested. Based on the proposed topology, a 2-D MIMO UWB array for high-resolution short-range imaging is developed. The focusing properties of this array are studied both theoretically and experimentally and are shown to be superior to those of arrays with a similar number of antennas and based on known topologies such as Mills Cross, rectangular, and spiral configurations. Decisive impact of a large operational bandwidth and short focusing distance on MIMO array performance is shown. Imaging capabilities of the proposed array are experimentally demonstrated for distributed targets.

Comparison of UWB technologies for human being detection with radar

UWB radar for detection and positioning of human beings in complex environment can be developed based on different technologies such as video impulse, quasi-random noise, stepped-frequency continuous wave and frequency-modulated continuous wave. These technologies are compared on the basis of meeting functional requirements to such a radar. Relative advantages and disadvantages of these technologies for such an application as human being detection and positioning are pointed out. Recommendations for selection of an optimal technology are given.

Assessment of Electromagnetic Requirements for UWB Through-Wall Radar

This paper investigates electromagnetic requirements for ultra-wideband (UWB) through-wall radar. It includes the evaluation of propagation loss, dynamic range and radar resolution for typical through-wall scenarios. The evaluation results in analysis and comparison of different transmission schemes.

UWB MIMO Antenna Array Topology Design Using PSO for Through Dress Near-field Imaging

In this paper two novel MIMO UWB antenna arrays have been proposed for through dress imaging radar application. The advantage of using MIMO array is that the number of elements can be reduced and the element spacing can be sparser than that of SIMO array, while the performance will be almost the same. Particle swarm optimization (PSO) method is used to determine the optimum antenna array topologies for different scenarios that can provide sufficient cross-range resolution and an acceptable mainlobe to side lobe level. The results demonstrated that by properly design the fitness function, we can trade off the cross-range resolution and mainlobe to sidelobe ratio and find proper array topologies for different scenarios.

Subsurface Imaging with UWB Linear Array: Evaluation of Antenna Step and Array Aperture

This paper presents the investigation of antenna step and aperture size for an ultra-wideband (UWB) ground penetrating radar (GPR) with a linear array. The procedure includes the optimization of receiving array, verification of optimization results by EM simulation and experimental measurement for both surface and subsurface imaging. The imaging algorithm used for the evaluation combines the focusing of the array and the synthetic aperture radar technique in the mechanical scan direction.

Ultra-wideband imaging for detection of early- stage breast cancer

Ultra-wideband imaging for medical applications has been of interest for many years due to its high resolution and capability of detection and classification. In this paper, ultra-wideband near-field imaging is applied for detection of small malignant tumors inside breasts. Multiple antenna and focusing algorithm are used to form a spatial image of reflectivity, and to identify the presence and location of malignant lesions from their scattering signatures. The method is demonstrated by successful detection of a 2 mm diameter tumor in a three-dimensional numerical breast model.