Near-field Radar Research Articles

Near-Field Radar Imaging Using MMIC-Based Large-Aperture Array

Near-Field Radar Imaging Using MMIC-Based Large-Aperture Array

Near-Field Radar Equation Based on Fresnel Diffraction Formula to Detect Short-Ranged Targets for Automotive Radar

Although the classic radar equation has been widely used to analyze the link budget of an automotive radar, it is valid only when the targets are located in the far-field region of the transmitted field and the receiving antenna is located in the far-field region of the scattered field. This paper confirms this hypothesis using measured and simulated data for short-range radars. Furthermore, a novel radar equation based on the Fresnel diffraction formula is proposed for application in situations where the receiving antenna is located in the radiative near-field region (or Fresnel region) of a target, but the target is situated in the far-field region of the transmitting antenna. In addition, the proposed radar equation is assessed by comparing the measured and simulated data.

Efficient Near-Field Radar Microwave Imaging Based on Joint Constraints of Low-Rank and Structured Sparsity at Low SNR

Efficient Near-Field Radar Microwave Imaging Based on Joint Constraints of Low-Rank and Structured Sparsity at Low SNR

Fast Factorized Kirchhoff Migration Algorithm for Near-Field Radar Imaging With Sparse MIMO Arrays

Fast Factorized Kirchhoff Migration Algorithm for Near-Field Radar Imaging With Sparse MIMO Arrays

Fast, Fully-Automatic Characterization of Metallic and Water-Based Threat Objects for Millimeter-Wave Personnel Screening Systems

Efficient characterization of concealed person-worn objects enhances the security of air travel and reduces the inspection time. Mm-wave nearfield radar can detect metallic objects such as guns or knives, as well as water-based materials that might be associated with peroxide threats. However, it cannot discriminate these potential threats from benign objects to decrease the nuisance alarm rate. Moreover, distinguishing these potential threats from benign objects in the presence of human skin is even more challenging. The authors have previously developed a method using mm-wave imaging to estimate the nominal body contour (NBC) with attached objects. This paper extends the image-processing-based algorithm to identify concealed metallic and water-based objects, as thin as 1 cm, attached to arms, legs, torso, and the pelvic region. The algorithm determines if the anomaly in the image is due to lossless or conductive material seen respectively as a depression or protrusion relative to the NBC. Next, high-loss water-based objects are distinguished from metallic and benign low-loss objects. The developed method is verified experimentally via actual images of human subjects, with foreign attached objects of various types and sizes. The images were captured by the High Definition-Advanced Imaging Technology (HD-AIT) scanner, a laboratory prototype system developed recently by the U.S. Department of Homeland Security (DHS). The developed codes resulted in zero miss and 7% rate of false alarm, while the rest of objects were either characterized correctly or referred to for a secondary pat down. Our method is performed fully-automatically and within a few seconds.

Preliminary Results of a New Auxiliary Mechatronic Near-Field Radar System to 3D Mammography for Early Detection of Breast Cancer.

Accurate and early detection of breast cancer is of high importance, as it is directly associated with the patients’ overall well-being during treatment and their chances of survival. Uncertainties in current breast imaging methods can potentially cause two main problems: (1) missing newly formed or small tumors; and (2) false alarms, which could be a source of stress for patients. A recent study at the Massachusetts General Hospital (MGH) indicates that using Digital Breast Tomosynthesis (DBT) can reduce the number of false alarms, when compared to conventional mammography. Despite the image quality enhancement DBT provides, the accurate detection of cancerous masses is still limited by low radiological contrast (about 1%) between the fibro-glandular tissue and affected tissue at X-ray frequencies. In a lower frequency region, at microwave frequencies, the contrast is comparatively higher (about 10%) between the aforementioned tissues; yet, microwave imaging suffers from low spatial resolution. This work reviews conventional X-ray breast imaging and describes the preliminary results of a novel near-field radar imaging mechatronic system (NRIMS) that can be fused with the DBT, in a co-registered fashion, to combine the advantages of both modalities. The NRIMS consists of two antipodal Vivaldi antennas, an XY positioner, and an ethanol container, all of which are particularly designed based on the DBT physical specifications. In this paper, the independent performance of the NRIMS is assessed by (1) imaging a bearing ball immersed in sunflower oil and (2) computing the heat Specific Absorption Rate (SAR) due to the electromagnetic power transmitted into the breast. The preliminary results demonstrate that the system is capable of generating images of the ball. Furthermore, the SAR results show that the system complies with the standards set for human trials. As a result, a configuration based on this design might be suitable for use in realistic clinical applications.

A compressive sensing approach for enhancing breast cancer detection using a hybrid DBT/NRI configuration

This work presents a novel breast cancer imaging approach that uses compressive sensing in a hybrid digital breast tomosynthesis (DBT)/nearfield radar imaging (NRI) system configuration. The non-homogeneous tissue distribution of the breast, described in terms of dielectric constant and conductivity, is extracted from the DBT image, and it is used by a full-wave finite difference in the frequency domain method to build a linearized model of the non-linear NRI imaging problem. The inversion of the linear problem is solved using compressive sensing imaging techniques, which lead to a reduction on the required number of sensing antennas and operational bandwidth without loss of performance.

Preliminary imaging results and SAR analysis of a microwave imaging system for early breast cancer detection.

Currently X-ray-based imaging systems suffer from low contrast between malignant and healthy fibrous tissues in breast. Microwave Near-field Radar Imaging (NRI) shows a higher contrast between the aforementioned tissues and therefore can enhance tumor detection and diagnosis accuracy. In this work, we present the first imaging results of our developed NRI system that is equipped with a pair of Antipodal Vivaldi Antennas. We used a metal bearing ball immersed in oil as our object of interest, to keep the first measurement configuration simple. Moreover, to demonstrate the safety of our system for human subject tests, we simulated the Specific Absorption Rate (SAR) in a realistic breast tissue model and compared the resulted values with both the USA and Europe standards. The results show that firstly the imaging results from the measurements and simulations are comparable, and secondly the antennas radiations meet the SAR criteria.

Near-Field Radar Imaging via Compressive Sensing

A novel two-dimensional (2-D) compressive sensing (CS) based method is presented for near-field radar imaging. First, an accurate near-field approximation is proposed, based on which the circular wavefront curvature of spherical waves can be compensated by mapping the images to a rectified new grid. More importantly, the near-field approximation makes the two dimensions of the scattered data separable for the range and cross-range directions, which makes it possible to solve the 2-D reflectivity matrix for the image reconstruction directly. Then, a 2-D proximal subgradient algorithm for near-field radar imaging based on a fast iterative shrinkage/thresholding algorithm (FISTA) is introduced to resolve the memory usage and computation time issues. Simulation and experimental results are provided to demonstrate the performance of the proposed method with comparisons to the traditional Fourier-based method and to the conjugate gradient (CG) based method, which proves that the proposed method is an effective way to solve the near-field radar imaging problem.

Full-Wave Modeling of Near-Field Radar Data for Planar Layered Media Reconstruction

A new near-field radar modeling approach for wave propagation in planar layered media is presented. The radar antennas are intrinsically modeled using an equivalent set of infinitesimal electric dipoles and characteristic, frequency-dependent, global reflection, and transmission coefficients. These coefficients determine through a plane wave decomposition wave propagation between the radar reference plane, point sources, and field points. The interactions between the antenna and layered medium are thereby inherently accounted for. The fields are calculated using 3-D Green's functions. We validated the model using an ultrawideband frequency-domain radar with a transmitting and receiving Vivaldi antenna operating in the range 0.8-4 GHz. The antenna characteristic coefficients are obtained from near- and far-field measurements over a copper plane. The proposed model provides unprecedented accuracy for describing near-field radar measurements collected over a water layer, the frequency-dependent electrical properties of which were described using the Debye model. Layer thicknesses could be retrieved through full-wave inversion. The proposed approach demonstrated great promise for nondestructive testing of planar materials and digital soil mapping using ground-penetrating radar.

Ultrawideband Multi-Static Scattering Analysis of Human Movement Within Buildings for the Purpose of Stand-Off Detection and Localization

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.

Deterministic Approach for Spatial Diversity Analysis of Radar Systems Using Near-Field Radar Cross Section of a Metallic Plate

A deterministic analysis of spatial diversity is presented in connection with radar systems. A numerical technique based on physical optics is used for our analysis. Contrary to statistical models, the proposed technique takes into account accurate near-field radar cross section of the target, and radiation characteristics of transmitting and receiving antennas. The power scattered by the target and received by multiple antennas as a function of the target aspect angle and distance is analyzed. Two combining methods of received powers are tested and statistical analysis is performed showing that, using spatial diversity, the angular range can be increased significantly and the standard deviation of the target response can be reduced. In order to validate our analysis and proposed scheme, experimental measurements were carried out using a metallic plate and a car as targets. This work has potential applications in automotive collision warning/avoidance radar systems.

Improved Near-Field Radar Cross-Section Measurement Technique

This letter presents an improved image-based coherent Doppler tomography (CDT) technique for near-field radar cross-section measurement. The present formulation, developed using the back-projection algorithm, explicitly incorporates the network analyzer calibration in the near-field to far-field transformation. Experimental measurements and computer simulations are presented to validate the improved CDT technique.

Radiation effects in near-field microwave diagnostics

Radiation effects in the near-field diagnostics of weakly absorbing dielectrics are studied theoretically and experimentally. Calculations are performed on the basis of the developed theory of the near-field radar of a plane-layered medium, which is used for calculation of the complex impedance of a probe situated above the interface of a homogeneous medium and an inhomogeneous medium. It is found that the height dependence of the active part of impedance is characterized by “wave” spatial scale hw, whereas the reactive part has quasistatic scale hqs, where hqs ≪ hw. It is revealed that the response of a near-field radar contains a parameter sensitive to the radiation fields of the probe. It is shown that recording of this parameter can substantially extend the sensing volume of near-field radar.

Focused Gaussian beams in the problem of holographic imaging

A simplified scheme of microwave near-field radar is considered. Focused Gaussian beams form a functional basis for holographic migration. Two-frequency phase measurements are used for the target localization. Numerical examples are given.

Noise Radar Technology

Noise radar technology (NRT) is based on using a continuous (or quasi-continuous) noise signal (CNS) as a sounding one and correlation (or double spectral) processing of reflected radar signals for their optimal reception (matched filtering). NRT shows much promise for the application in the near-field radar and is adequate to the present-day microwave and electronic technologies. There are two types of noise radars. One of them utilizes the correlation processing of reflected signals, and another is based on the so-called double spectral processing. As shown in experiments, NRT can be successfully used by developing radars for various civil applications, e.g. anticollision systems, automated traffic control, obtaining the images by ground-based synthetic aperture radars automated aircraft landing and ship mooring, etc.