This PDF file contains the front matter associated with SPIE Proceedings Volume 6947, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Measurements were performed by The Army Research Laboratory (ARL) to characterize the statistical and discrete radar clutter at Ka-Band frequencies associated with urban environments for the purpose of investigating the associated backscatter physics and to generate statistics of large extended targets. The measurement data will be used to develop waveform and radar signal processing requirements for Ka-Band radar sensors in urban operational environments. The peak Radar Cross Section (RCS) statistics for urban clutter data are presented as Probability Distribution Functions and Cumulative Distribution Functions.

Ultra-wideband (UWB) signals exhibit different characteristics upon propagation through matter compared with narrowband signals. The latter keeping a sinusoidal shape during different forms of signal propagation. The behavior of narrowband signals does not apply to UWB signals in many cases. Presently, the possibilities for development of UWB signaling technology remain largely unexplored. Only a few applications have been developed due to strict regulations by the Federal Communications Commission (FCC). In this paper we describe a series of experiments that have been carried out to determine the behavior of UWB signals and their properties. A TEM horn antenna has been made for radiating UWB signals. Experiments on pulse propagation have been carried out including an application to detection of stationary metal objects. A high accuracy in detecting metal objects has been achieved. A procedure for propagating UWB signals through a liquid medium of given salt concentration has been demonstrated, providing a basis for studying UWB signal propagation in biological matter. A new pulsewidth definition was adopted which is suitable for UWB signal propagation.

Coherent Change Detection (CCD) is a technique for observing very subtle changes between two Synthetic Aperture Radar (SAR) images. It is an Interferometric processing technique that measures the coherence between two images, and denotes 'change' where coherence is not observed, and 'no change' where coherence is observed. Consequently, the strategy must be to form both images with as much initial coherence as possible, and then see where in spite of our best efforts coherence cannot be achieved. Many things contribute to destroying coherence, but we want to eliminate all sources except for temporal change in the scene being imaged itself. This requires that a number of variables in the data collection be well controlled, and that the processing must be adapted to mitigate the effects of residual imperfections to achieve maximum coherence. It must be emphasized that the coherence calculation, that is, calculating the actual CCD product from two images is the easy part. The hard part is making sure that the two input images have the underlying characteristics to yield a quality result. The purpose of this paper is to discuss "What it takes to get good CCD results."

There has been little interest in the information associated with the shadows in high resolution Synthetic Aperture Radar (SAR) images. In this paper we give an algorithm for the reconstruction of an object's shape from the shadows cast by the object in a sequence of SAR images. The algorithm is a back-projection type algorithm based on the intersection of solids. The effects of diffraction and synthetic aperture occlusion on SAR shadow resolution are also addressed.

The Army Research Laboratory (ARL) has recently developed the ground-based synchronous impulse reconstruction (SIRE) radar - a low-frequency radar capable of exploiting both a real antenna array and along-track integration techniques to increase the quality of processed imagery. We have already demonstrated the system's utility by imaging static scenes. In this paper we address the moving target indication (MTI) problem, and we demonstrate the impulse-based system's ability to both detect and locate slowly moving targets. We begin by briefly describing the SIRE system itself as well as the system configuration utilized in collecting the MTI data. Next we discuss the signal processing techniques employed to create the final MTI image. Finally, we present processed imagery illustrating the utility of the proposed method.

An important task in urban sensing operation is accurate estimation and positioning tracking of moving targets. Equally important is target identifications and classifications based on distinctions in the respective motion signatures, such as targets encountering translation versus rotation or vibration motions or targets exhibiting linear versus nonlinear motions. Dual-frequency radars, which estimate the range of a target based on the phase difference between two closely spaced frequencies, have been shown to be a cost-effective method for this purpose. In particular, when time-frequency signal representation techniques are incorporated, Doppler signature enhancement and localization in the time-frequency domain enables robust range estimation of multiple targets with different motion profiles and small radar cross-sections. In this paper, the dual-frequency radar concept is extended to develop a narrowband (NB) frequency-hopping (FH) radar. The proposed NB-FH radar provides multifold advantages such as low probability of intercept, low interference to/from other systems, and flexible bandwidth usage for the improvement of range accuracy and phase unwrapping.

Change detection provides a powerful tool for detecting the introduction of weapons or hazardous materials into an area under surveillance, as demonstrated in past work carried out at the Army Research Laboratory (ARL). This earlier work demonstrated the potential for detecting recently emplaced surface landmines using an X-Band, synthetic aperture radar (SAR) sensor. Recent experiments conducted at ARL have extended these change detection results to imagery collected by the synthetic impulse reconstruction (SIRE) radar - a lower-frequency system developed at ARL. In this paper we describe the algorithms adopted for this change detection experiment and present results obtained by applying these algorithms to the SIRE data set. Results indicate the potential for utilizing systems such as the SIRE as surveillance tools.

The U.S. Army Research Laboratory (ARL), as part of a mission and customer funded exploratory program, has developed a new low-frequency, ultra-wideband (UWB) synthetic aperture radar (SAR). The radar is capable of penetrating enclosed areas (buildings) and generating SAR imagery. This supports the U.S. Army's need for intelligence on the configuration, content, and human presence inside these enclosed areas. The radar system is mounted on a ground based vehicle traveling along the road and is configured with an array of antennas pointing toward the enclosed areas of interest. This paper will describe an experiment conducted recently at Aberdeen Proving Ground (APG), Maryland. In this paper we briefly describe the UWB SIRE radar and the test setup in the experiment. We will also describe the signal processing and the image techniques used to produce the SAR imagery. Finally, we will present SAR imagery of the building and its internal structure from different viewing directions.

Through-the-wall imaging (TWI) is a challenging problem, even if the wall parameters and characteristics are known to the system operator. Proper target classification and correct imaging interpretation require the application of high resolution techniques using limited array size. In inverse synthetic aperture radar (ISAR), signal subspace methods such as Multiple Signal Classification (MUSIC) are used to obtain high resolution imaging. In this paper, we adopt signal subspace methods and apply them to the 2-D spectrum obtained from the delay-andsum beamforming image. This is in contrast to ISAR, where raw data, in frequency and angle, is directly used to form the estimate of the covariance matrix and array response vector. Using beams rather than raw data has two main advantages, namely, it improves the signal-to-noise ratio (SNR) and can correctly image typical indoor extended targets, such as tables and cabinets, as well as point targets. The paper presents both simulated and experimental results using synthesized and real data. It compares the performance of beam-space MUSIC and Capon beamformer. The experimental data is collected at the test facility in the Radar Imaging Laboratory, Villanova University.

There has been continuing interest in the penetration of multilayer building materials, such as wood walls with air gaps and concrete hollow core block, using through-the-wall (TTW) radar systems. TTW operational techniques and signal propagation paths vary depending on how the TTW system is intended to be operated. For example, the operator of a TTW radar may be required to place the radar against the intervening wall of interest while collecting data. Other operational doctrines allow the radar to be operated in a stand-off mode from the wall. The stand-off distances can vary from feet to hundreds of feet, depending on the type of radar being used. When a signal is propagated through a multilayer wall with air gaps between the material and the wall construction uses materials of radically different dielectric constants, attenuation may not be the only effect that the probing signal experiences passing through the wall. This paper presents measurements of a hollow core concrete block wall and the measurement of a standard wall constructed of siding and wallboard. Both types of walls are typically found in most U.S. homes. These limited measurements demonstrate that the type of wall being penetrated by a wideband signal can modify the probing signal.

The Army Research Laboratory (ARL) has been engaged in an effort to support the "See through the Wall" initiative. As part of the effort, we have explored the possibilities and challenges of using data collected by small groups of men - each man equipped with a small, hand-held, Radio Frequency (RF) sensor - to image the interior of buildings. We examine various multi-static combinations of sensors, especially in configurations that allow for imaging a room from different viewing angles, and we demonstrate the capability of these approaches for providing comprehensive information about a building's interior. We examine the consequences of errors in the assumed position of the RF sensors, and we analyze the effects of the degradation of signal coherence due to mistiming. Simulation results are provided to show the potential of this type of sensor arrangement in such a difficult, urban environment.

This paper sets an optimization criterion to maximize the performance from a given aperture by providing the geometrical locations of the antenna elements in a 'Through Wall Imaging' (TWI) system. In many real life applications there are strict constraints on the aperture size of TWI systems in order to have portable, easy to carry and light weight systems. Therefore it becomes very important to maximize the information capacity of objects behind the wall from a given physical dimension. A mathematical formulation is proposed herein to quantify the performance of any proposed geometry of an antenna array. A few examples for specific configurations are also presented and compared in different SNR conditions.

The usage of ultra-wideband (UWB) technology is growing in many communication systems such as radar systems, communication and measurement systems and imaging systems mainly because unlike the other wireless technologies UWB is not restricted to using a narrow waveband and it has high speed data rate. The large transmission bandwidth makes UWB-based electronic device resistive to interferences and gives immunity against getting detected. Typical operational frequency range of the UWB devices varies from few 100s MHz to 10 GHz. However, the most popular UWB devices are designed to operate between 1-3 GHz. This paper presents an overview of different types of commercially available antennas suitable for UWB applications. The paper begins with the basics of understanding of antennas properties. Next, it discusses the main antenna characteristics like: radiation pattern (directional or omni-directional), gain, bandwidth, size, etc for different UWB applications and explains criterions for quantitative and qualitative performance measure of the antennas. The antennas covered in this paper include: TEM Horn, Folded horn, Dipole, Planner Fat Dipole, Cross Dipole, Rolled Dipole, UWB dielectric, Bowtie, Wire Bowtie, etc. This paper describes the pros and cons of each antenna and highlights the application areas of each antenna. Lastly, this paper summaries the important characteristics of the antennas and presents several promising directions for future enhancement of UWB antenna systems.

Frequency stepping is one of the known techniques employed by modern radars to attain high range resolution. One of the main advantages of this approach is that it allows to achieve wideband pulse compression through narrowband processing. It is also known that the traditional linear stepped-frequency waveform suffers from relatively high range sidelobes and grating lobes that appear due to periodicities in the Discrete Fourier Transform (DFT). An amplitude weighting (applied prior to the DFT) is typically used to reduce the near-in sidelobes. This results in undesirable losses in sensitivity. In this paper, we propose a new approach that may be used to derive families of nonlinear stepped-frequency waveforms that would have desired characteristics such as suppressed grating lobes and built-in low range sidelobes. Our approach is based on new analytical properties of stepped-frequency waveforms presented in the paper. We give examples of nonlinear waveforms generated by this approach and show that they exhibit improved performance when compared with traditional waveforms.

In this paper, two-dimensional (2D) (range and azimuth) resolution enhancement is investigated for millimeter wave (mmW) real-beam radar (RBR) with linear or non-linear antenna scan in the azimuth dimension. We design a new architecture of super resolution processing, in which a dual-mode approach is used for defining region of interest for 2D resolution enhancement and a combined approach is deployed for obtaining accurate location and amplitude estimations of targets within the region of interest. To achieve 2D resolution enhancement, we first adopt the Capon Beamformer (CB) approach (also known as the minimum variance method (MVM)) to enhance range resolution. A generalized CB (GCB) approach is then applied to azimuth dimension for azimuth resolution enhancement. The GCB approach does not rely on whether the azimuth sampling is even or not and thus can be used in both linear and non-linear antenna scanning modes. The effectiveness of the resolution enhancement is demonstrated by using both simulation and test data. The results of using a 94 GHz real-beam frequency modulation continuous wave (FMCW) radar data show that the overall image quality is significantly improved per visual evaluation and comparison with respect to the original real-beam radar image.

Getting to wounded soldiers on the battlefield is a precarious task, and medics have a very high casualty rate. It is therefore a vital importance to prioritize which soldiers to attend to first. The first step is to detect life signs - if a soldier is dead or alive, and prioritize recovery of live soldiers. The second step is to obtain vital signs from live soldiers, and use this to prioritize which are in most urgent need of attention. Our team at Kai Sensors, University of Hawaii and University of Florida is developing Doppler radar heart sensing technology that provides the means to detect life signs, respiration and/or heart beat, at a distance, even for subjects lying motionless, e.g., unconscious subjects, wearing body armor, and hidden from direct view. Since this technology can deliver heart rate information with high accuracy, it may also enable the assessment of a subject's physiological and psychological state based on heart rate variability (HRV) analysis. Thus, the degree of a subject's injury may also be determined. The software and hardware developments and challenges for life signs detection and monitoring for battlefield triage will be discussed, including heart signal detection from all four sides of the human body, detection in the presence of body armor, and the feasibility of HRV parameter extraction.

The sense through the wall research community has depended upon a number of studies and a few key sets of measured data on large wall test samples for analysis, development, and design of critical hardware, software, and systems. New and improved testing technology has now been used to acquire, post process, and analyze measured data sets. The Intelligence & Information Warfare Directorate (I2WD) has made it a priority to realize the benefits of new technology to improve upon and add detail to existing data, while exploring completely new test methodologies. These factors have provided the basis for a new comprehensive test plan for the RF characterization of wall samples used in the past at the I2WD wall testing facility located at CACI Technologies in Eatontown, NJ. In addition, there will be future testing of new material composition samples will be characterized. Our first phase of testing investigates the permittivity of large scale wall samples. The wall samples used for our testing were constructed using "real world" type conventional construction techniques (see 1.1.1). This paper will cover the RF characterization of these wall materials (basic frequency response, permittivity). The initial round of testing has seen the benefits of highly advanced RF test equipment and calibration techniques. Following these baseline tests, a future publication will cover advanced testing, which will explore near field vs. far field effects, moisture variations, angles of incidence, and polarization effects. Lastly, waveform testing will be performed to determine the best waveform techniques and their effectiveness in through wall applications.