Wenji Zhang

Through-the-Wall Target Localization with Time Reversal MUSIC Method

Time Reversal Multiple Signal Classiflcation (TR-MUSIC) method is studied and adapted for the detection and localization of multiple targets behind the wall in this paper. TR-MUSIC does not involve the FDTD solver for the implementation of the backpropagation of the time reversed fleld and is very computational e-cient. The Greens function vectors for the computation of the TR-MUSIC pseudo-spectrum is e-ciently evaluated with the saddle point method for a homogeneous wall. By employing the null space of the multistatic response matrix, simultaneous localization of multiple targets behind the wall can be achieved by TR-MUSIC method. Numerical results are presented to show the efiectiveness of through- the-wall imaging (TWI) with TR-MUSIC method.

Ultrawideband Impulse Radar Through-the-Wall Imaging with Compressive Sensing

Compressive Sensing (CS) provides a new perspective for addressing radar applications requiring large amount of measurements and long data acquisition time; both issues are inherent in through-the-wall radar imaging (TWRI). Most CS techniques applied to TWRI consider stepped-frequency radar platforms. In this paper, the impulse radar two-dimensional (2D) TWRI problem is cast within the framework of CS and solved by the sparse constraint optimization performed on time-domain samples. Instead of the direct sampling of the time domain signal at the Nyquist rate, the Random Modulation Preintegration architecture is employed for the CS projection measurement, which significantly reduces the amount of measurement data for TWRI. Numerical results for point-like and spatially extended targets show that high-quality reliable TWRI based on the CS imaging approach can be achieved with a number of data points with an order of magnitude less than that required by conventional beamforming using the entire data volume.

Full polarimetric beam‐forming algorithm for through‐the‐wall radar imaging

[1]xa0Development of an imaging algorithm that accurately models the wave propagation physical process has become an important topic in through-the-wall radar imaging (TWRI). In this paper, a full polarimetric beam-forming algorithm for through-the-wall radar imaging for a general multilayer wall case is presented and applied to various 2D and 3D simulated and measured scenarios. Polarimetric TWRI not only enhances the target characterization but also mitigates the wall ringing effect in cross polarizations. The far field layered medium Greens function is incorporated in the proposed TWRI algorithm for the quad-polarization of the target returns, namely, VV, HV, VH and HH. Due to the incorporation of the layered medium Greens function, the imaging algorithm not only takes into account the wall reflection, bending, and delay effects but also accounts for the complex scattering mechanism due to the presence of the wall. Numerical and experimental results show that the proposed full polarimetric beam former can provide high quality focused images in various wall-target scenarios, in particular, when the technique is combined with a wall parameter estimation technique.

A compressive sensing approach to moving target indication for urban sensing

In this paper, we apply compressive sensing to moving target indication for urban sensing and through-the-wall imaging applications using stepped-frequency radar. In particular, we consider sparsity-driven imaging combined with change detection. Stationary targets and clutter are removed via change detection, resulting in a sparse scene of few slow-moving targets inside enclosed structures and behind walls. Using compressive sensing, a sizable reduction in the number of samples is achieved without degradation in system performance. Laboratory experiments are conducted to validate the proposed approach.

Three-Dimensional Synthetic Aperture Radar Imaging Through Multilayered Walls

Most of existing through-the-wall radar imaging (TWRI) algorithms deal with a single layer homogeneous wall in two-dimensional scenario. In this communication we present a generalized three-dimensional (3-D) beamforming algorithm for the focused imaging of targets behind multilayered building walls. The far field layered medium Greens function is incorporated in the 3-D beamformer for the compensation of the wall effect. 3-D polarimetric imaging is exploited in TWRI for enhanced target identification and feature extraction as well as wall effect mitigation. Numerical results show that the proposed 3-D beamformer provides high quality focused images in various wall-target scenarios.

A Generalized Approach for SAR and MIMO Radar Imaging of Building Interior Targets With Compressive Sensing

Most existing methods on compressive sensing (CS) for through-the-wall radar imaging (TWRI) are developed for monostatic synthetic aperture radar (SAR) and are only capable of target imaging behind a single-layer wall. In this letter, a generalized Greens function-based approach for the imaging of targets behind single- or multilayered building walls with CS is proposed. The approach is applicable to both SAR and multiple-input-multiple-output (MIMO) radar. By exploiting the sparsity of the target space, a less cluttered high-resolution image can be achieved with far fewer measurements. The number of antenna elements in the MIMO radar system can be significantly reduced using the proposed approach, resulting in an overall reduction of the complexity and cost of MIMO radar for TWRI applications. Numerical results are presented to show that high-quality focused image can be achieved under various wall-target scenarios for both SAR and MIMO radar.

TWO-DIMENSIONAL DIFFRACTION TOMOGRAPHIC ALGORITHM FOR THROUGH-THE-WALL RADAR IMAGING

In this paper, a two-dimensional (2D) difiraction tomographic algorithm based on the flrst order Born approximation is proposed for the imaging of hidden targets behind the wall. The spectral expansion of the three layered background medium Greens function is employed to derive a linear relationship between the spatial Fourier transforms of the image and the received scattered fleld. Then the image can be e-ciently reconstructed with inverse Fast Fourier Transform (IFFT). The linearization of the inversion scheme and the easy implementation of the algorithm with FFT/IFFT make the difiraction tomographic algorithm suitable in through-the- wall radar imaging (TWRI) applications concerning the diagnostics of large probed domain and allow real-time processing. Numerical and experimental results are provided to show the efiectiveness and high e-ciency of the proposed difiraction tomographic algorithm for TWRI.

Target RCS exploitations in compressive sensing for through wall imaging

In this paper, target radar cross-section (RCS) is utilized to improve the performance of compressive sensing (CS) when applied to sensing through wall based on RF modality. Using step-frequency SAR imaging, it is shown that the selection of frequencies emitted at each antenna position of the SAR system can benefit from a priori knowledge of the target RCS. Frequencies with high target response allow the CS performance to be more robust to noise and are able to reveal target presence in noisy and cluttered environments.

Boresight gain enhancement of an UWB planar monopole antenna

Techniques for boresight gain enhancement of an UWB planar monopole antenna is presented. The squinting effect of the radiation pattern in the broadside direction at high frequencies is alleviated through the introduction of a gate-like structure in the ground plane. The boresight gain is further improved by adding a parasitic element above the main patch.

Two- and Three-Dimensional Fast Intrawall Imaging with Microwave Tomographic Algorithm

A fast and efficient microwave tomographic algorithm is proposed for 2-D and 3-D real-time intrawall imaging. The exploding reflection model is utilized to simplify the imaging formulation, and the half-space Green’s function is expanded in the spectral domain to facilitate the easy implementation of the imaging algorithm with the fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT). The linearization of the inversion scheme and employment of FFT/IFFT in the imaging formula make the algorithm suitable for various applications pertaining to the inspection of a large probed region and allow real-time processing. Representative numerical and experimental results are presented to show the effectiveness and efficiency of the proposed algorithm for real-time intrawall characterization.