Adaptive Polarization Contrast Techniques for Through-Wall Microwave Imaging Applications

In this paper, we describe and utilize polarization contrast techniques of the adaptive polarization difference imaging algorithm and its transient modification for through-wall microwave imaging (TWMI) applications. Originally developed for optical imaging and sensing of polarization information in nature, this algorithm is modified to serve for target detection purposes in a through-wall environment. The proposed techniques exploit the polarization statistics of the observed scene for the detection and identification of changes within the scene and are not only capable of mitigating and substantially removing the wall effects but also useful in detecting motion, when conventional Doppler techniques are not applicable. Applications of the techniques to several TWMI scenarios including both homogeneous and periodic wall cases are presented

Application Of Antenna Synthesis And Digital Signal Processing Techniques For Active Millimeter-wave Imaging Systems

Millimeter-wave imaging has gathered attention in recent years for its ability to penetrate clothing, thin layers of soils, and certain construction materials. However, image quality remains a challenge that needs to be addressed. One way of improving image quality is by increasing the dimensions of the collecting aperture. A sparse array can be used to synthesize a larger aperture with a limited set of relatively small detectors. In this research we design, build, and test a test-bed having an active source at 94 GHz and an array of coherent detectors, mounted on arms that extend radially on a rotary table. Using this test bed a circular area with a maximum diameter of 900 mm can be scanned. The signal is down-converted using heterodyne receivers with digital in-phase and quadrature detection. Signal correlation is performed using the digitized data, which is stored for post-processing, electronic focusing, and image reconstruction. Near-field imaging using interferometric reconstructions is achieved using electronic focusing. Imaging tests show the ability of the system to generate imagery of concealed and unconcealed objects at distances between 400 and 700 mm. A study of the effects of redundant and nonredundant configurations on image quality for 4 common detector configurations is presented. In this document we show that an active sparse-aperture imaging system using digital correlators is a viable way to generate millimeter-wave images

ANALYSIS AND DESIGN OF ANTENNA PROBES FOR DETECTION / IMAGING APPLICATIONS

Analysis and Design of Antenna Probes for Detection / Imaging Applications Ayman Elboushi, Ph.D. Concordia University. As a result of increasing international terrorist threats, the need for an efficient inspecting tool has become urgent. Not only for seeing through wall applications, but also to be employed as a safe human body scanner at public places such as airports and borders. The usage of microwave and millimeter wave antennas and systems for detection / imaging applications is currently of increasing research interest targeting the enhancement of different security systems. There are many challenges facing researchers in order to develop such systems. One of the challenges is the proper design of a low cost, reduced size and efficient antenna probe to work as a scanning sensor. In this thesis, two different technology choices of antenna probes for the feasibility of constructing detection / imaging systems are investigated. The first one covers the Ultra Wide Band (UWB) range (3.1 GHz to 10.6 GHz), while the second operates over the Millimeter-Wave (MMW) range. In addition to the development of several antenna probes, two detection / imaging systems are demonstrated and showed reasonably accurate detection results. Three different UWB monopole antenna prototypes, with different radiator shapes (circular, crescent and elliptical) have been introduced. These antennas are designed using a standard printed circuit board (PCB) process to work as probing sensors in a proposed UWB detection / imaging system. In order to enhance the resolution and the detection accuracy of the probe, 4-element Balanced Antipodal Vivaldi Antenna (BAVA) array fed by 1-to-4 UWB modified Wilkinson power divider has been developed. Some successful experiments have been conducted using the proposed UWB detection / imaging system combined with the fabricated antenna probes to detect the presence of a gap between two walls made of different material types, to evaluate the gap width and to estimate the size and exact location of a hidden target between the walls. The second research theme of this thesis is to develop small-sized, light-weight and high gain MMW scanning antenna probes. For the realization of such probes, several gain enhancement techniques have been adopted, including hybridization and a multi-element array principle. Several high-gain hybrid antennas have been designed, fabricated and tested. For demonstration purposes, experiments have been carried out for detecting and imaging a small metallic coin under the jeans layer of a three-layer target emulating a human body’s covering layers. A performance comparison between a standard metallic MMW horn and hybrid microstrip patch/conical horn antenna has been made. The proposed reduced size antenna sensor shows increased efficiency compared with the bulky horn antenna. Resolution enhancement of the reconstructed image of the hidden target is implemented using a new triple-antenna MMW sensor. The triple-antenna sensor consists of three adjacent microstrip patch / conical horn antennas separated by 1.5 wavelengths at the center frequency for coupling reduction between these elements. The middle element of the sensor is used for monitoring the time domain back-reflected signal from the target under inspection, while the side elements are used for monitoring the scattered signals. By the aid of a special signal processing algorithm, an enhanced image of the concealed object can be obtained by combining the three readings of each point in the area under study. The proposed system shows a great ability for detecting a hidden target and enhances the reconstructed image resolution

Design and Time-domain Analysis of Antenna Array for UWB Imaging Application.

PhDUWB technology has been developing in imaging applications. For security imaging applications, it is vital to detect and image metallic targets concealed in bag at airports, subway stations or other public environments. To reduce the cost of the deployment of X-ray machines, a novel UWB imaging system has been developed, including the design of the UWB rotating antenna array, the design of RF circuits and the implementation of the two-dimensional delay-and-sum (DAS) image reconstruction method. Two types of UWB antennas, the circular-edge antipodal Vivaldi antenna and the corrugated balanced antipodal Vivaldi antenna (BAVA) have been designed and studied in both frequency domain and time domain. Both of them can work across UWB frequency range from 3.1 GHz to 10.6 GHz, and have directional radiation patterns. The corrugated BAVA with smaller physical size has been improved to have a relative high gain around 7 dBi across the operating frequency range. It also causes less distortion to signals in the time domain. So the corrugated BAVA is used as the antenna element in the UWB rotating antenna array. The UWB rotating antenna array comprises one central transmitting antenna and four receiving antennas. The receiving antennas, which rotate around the central transmitting antenna, are placed side-by-side on a straight arm. The equivalent antenna elements in space are increased by the rotation of the antenna array. The two-dimensional image reconstruction method has been developed based on DAS algorithm. This UWB imaging system can detect and reconstruct the image of the single and pairs of metallic targets concealed in bag. The smallest single target with the size of 4 cm × 4 cm × 1 cm can be reconstructed in images at a maximum distance of 30 cm away from the system. It can achieve 6 cm in cross-range resolution and 15 cm in down-range resolution. Therefore, the feasibility of the proposed UWB imaging system has been proved