Ultrawideband Radar – Applications and Design

Ultrawideband Radar – Applications and Design

If I write a book, a sophomore disputes me, an idiot condemns me, a parish priest accuses me of heresy and my wine merchant cuts off my credit. Each night I pray, “Dear God, deliver me from the itch to write books.”

Voltaire (1685–1778)

History of Ultrawideband Radar Applications and Design

I have watched ultrawideband (UWB) radar technology develop over almost a quarter century. My two previous books, Introduction to Ultra-Wideband Radar Systems (CRC Press 1995) and Ultra-Wideband Radar Technology (CRC Press 2000), presented state-of-the-art technology, system demonstrations, and the theory of UWB radar technology. I thought I had escaped from the subject until the editors of CRC Press asked me about revising my previous books. After looking at the advances of UWB radar technology and the potential applications developed, I proposed to write a book to present the latest progress in UWB radars.

People do not buy technology; they buy the benefits it gives them. Given the potential benefits, I believe that UWB radar will continue to evolve and gain importance as it finds more practical applications. Proposed applications from toilet-flushing sensors to cancer detection give some idea of the many potential uses of the radar. The publication of American and European emission spectrum standards in 2002 and the advances in integrated circuit technology have encouraged new applications of UWB radar in areas such as security and medicine. Eventually, we could see the use of UWB radar sensors in homes, public places, automobiles, doctors’ offices, hospitals, aircraft, military and police.

You will find chapters showing practical examples of the UWB radar theory, applications, and design. The chapters will cover history, government regulations, propagation theory, and examples of precision ranging in material-penetrating, imaging, and medical applications. You will find data regarding properties of materials and propagation theory.

I wish to thank my writers for their cooperation with my aggressive editing and revisions to their contributions.

Chapter Summaries

Chapter 1, “Ultrawideband Radar Applications and Design,” by James D. Taylor of J.D. Taylor Associates, summarizes the features and benefits of UWB radar. It starts with definitions and some history of how the term UWB evolved. UWB now has several different definitions set by the IEEE and government regulations. You will find a summary of the definitions, illustrating the similarities and differences among various definitions. Literature on UWB radar has grown over the past 20 years, and you will find a list of use­ful books on this subject.

Understanding UWB radar signals requires a shift in thinking from the traditional fre­quency domain steady-state analysis covered in most electronics books. The short dura­tion of UWB signals requires consideration and analysis in the time domain to include transient effects. The final sections of the chapter summarize the potential applications of UWB radar. The chapter ends with the description of an ideal future system combining all the latest technologies for small-target detection.

Chapter 2, “Development of Ultrawideband Communications Systems and Radar Systems,” by Terence W. Barrett, presents a comprehensive history of the development of UWB radio and radars. The chapter identifies many people who have helped develop the basic theory and technology of UWB radars and presents an updated version of articles originally published in the Microwave Journal and RF Design Magazine in 2001. You will also find an extensive bibliography of UWB-related materials.

Chapter 3, “Signal Waveform Variations in Ultrawideband Wireless Systems: Causes and Aftereffects,” was written by Igor Y. Immoreev of the Moscow Aviation Institute. Dr. Immoreev has studied the theory of UWB propagation for years. Very short (nanosec­ond, picosecond) duration (or short autocorrelation function) UWB wireless signals have major changes in their waveform during transmission and reception, which do not occur in narrowband signals. He shows how UWB signals with a physical length cτ equal or shorter than the radiating and receiving antennas and/or radar target dimensions will cause changes in waveform in the process of transmission, reception, and reflection. These changes in the signal waveform do not allow the use of traditional signal correlation recep­tion and require new signal-processing methods. Dr. Immoreev develops the theory and shows analytical methods for predicting how signal waveforms change the characteristics of radar systems. These changes require a new radar equation that uses only the radar energy characteristics of the antenna energy directivity factor of the antennas and the tar­get energy radar cross-section (RCS). He also shows how radiation and reception antenna patterns change, which means that the antenna radiating pattern differs from the antenna reception pattern, thereby making it impossible to use the familiar reciprocity principle. His theoretical development of how and why UWB signal waveforms change can help optimize system designs and exploit the benefits of an information-rich signal.

Chapter 4, “American and European Regulations on Ultrawideband Systems,” by James D. Taylor, presents extracts of the official rules governing the emission limits of unlicensed UWB systems. Because of the legal nature of this subject, appropriate parts of the regula­tions appear in their exact original wording to eliminate any possibility of confusion. Read these carefully because the emission limits as stated come from specified measurement procedures and have special meanings. You will find an initial guide for engineers plan­ning to develop unlicensed UWB radars and radio devices. I recommend this chapter to insomniacs for bedtime reading.

Chapter 5, “Principles of Materials Penetrating Ultrawideband Radar Systems,” by James D. Taylor, presents the basic theory of radar systems described in this book. Material pen­etrating UWB radar (MPR) systems work through multilayered media such as soil, rock, concrete, wood, air, and animal tissue. The general category includes ground-penetrating, through-wall, mine-detecting, and medical UWB measuring and imaging systems. Remote sensing through several media presents special problems because of the varying propaga­tion velocity, signal attenuation, and reflections from changes in the electrical properties of the media. This chapter summarizes the basic theory of MPR technology. The particular electrical characteristics of the media, such as conductivity, permittivity, and permeability, will drive your selection of an operating frequency range and the choice of the waveform. The contrast of targets and surrounding media will strongly affect the performance of the radar. Topics include applications, operating principles, frequency selection, and examples of the imaging capabilities of MPR systems.

Chapter 6, “Ultrawideband and Random Signal Radar,” by Dr. Hongbo Sun of the Nanyang Technological University, Singapore, shows how to use microwave noise signals for random noise-modulated waveforms. Conventional impulse-type radars described in other parts of this book have disadvantages in terms of low signal energy, which limits the performance of the radar. Using UWB random noise signals provides an alternative approach to increasing the signal bandwidth and resolution while increasing the signal energy. Some common designations of the random signal radars include noise modulation radar, correlation radar, random noise radar, spread spectrum radar, etc. Section 6.1 sum­marizes the history of the random signal radar and describes three typical implementation architectures and two processing schemes of this radar. Section 6.2 examines the combi­nation of UWB technology and random signal radar, including random signal genera­tion of carrier-modulated random signal radar and carrier-free radar with random coding. Section 6.3 presents the benefits of the UWB random signal radar, including the anti-RFI capability, low probability of interception (LPI) property, and electromagnetic compatibil­ity (EMC). Section 6.4 shows some typical applications of the UWB random signal radar to high-resolution imaging and measurement.

Chapter 7, “Automatic Measurement of Ground Permittivity and Automatic Detection of Object Location with GPR Images Containing a Response from a Local Object,” by Mikhail M. Golovko and Gennadiy P. Pochanin of the Usikov Institute of Radiophysics and Electronics of the National Academy of Sciences of Ukraine, Kharkov, Ukraine, shows how responses of the ground-penetrating radar can help detect water and oil leaks from buried pipelines and determine soil moisture content for hydrological and agricultural purposes. Because interpretation of ground-penetrating radar data requires complicated processing, the automation of object-detection process and ground-permittivity measure­ment with GPR images has great commercial implications. The authors present an auto­mated approach for evaluating the characteristics of ground by estimating the permittivity of ground from UWB radar responses.

Chapter 8, “UWB Pulse Backscattering from Objects Located near Uniform Half-Space,” by Oleg I. Sukharevsky and Vitaliy A. Vasilets of the Kharkov University of Air Forces, Kharkov, Ukraine, and Stanislav A. Gorelyshev of the Academy of the Interior Forces of the Ministry of Internal Affairs of Ukraine, Kharkov, Ukraine, presents a theory of backscat­tering of UWB pulse signal from perfect electrically conducting (PEC) large objects. The analysis considers targets located near the boundary of uniform half-space with both real and complex electrical parameters. Their approach uses the high-frequency (physical optics approach) approximation of impulse (transient) wavefront characteristics to calculate the UWB object reflected signal response by convolution transformation. The calculation method uses developed field integral representations and the high-frequency approximation of the pulse characteristics of a PEC object in a general bistatic case for oblique incidence. This also examines the problem of UWB signal scattering on the half-space representing a layered uniform medium with arbitrary layers of complex permeabilities. These analytical methods have many potential applications for estimating UWB signal responses from large targets.

Chapter 9, “Medical Applications of Ultrawideband Radar,” by James D. Taylor, presents an overview of the theory and applications for medical diagnosis and imaging. Medical applications have developed over the past 20 years, starting with the concept of a radar stethoscope based on the Lawrence Livermore National Laboratory’s micropower impulse radar. U.S. Air Force–sponsored studies have started building tables of electrical proper­ties of human tissue. The work of Igor Immoreev and Teh-Ho Tao explains the theory and techniques of remote measurement of heart rate and respiration rate. You will find examples of devices for quickly detecting intracranial hematoma and pneumothorax by emergency medical personnel. A final section discusses potential radar and tomographic applications for detecting breast cancers and other types of cancers. Economical UWB radar-based imaging and diagnostic systems could provide greater diagnostic capabilities to remote clinics and emergency medical specialists.

Chapter 10, “Large Current Radiators: Problems, Analysis, and Design,” by Gennaidy P. Pochanin and Sergey A. Masalov of the Usikov Institute of Radiophysics and Electronics of the National Academy of Sciences of Ukraine, Kharkov, Ukraine, presents the physical and technical problems arising during design of large current radiators (LCRs) and ways to overcome them. In contrast to the conventional electric dipole antenna, the LCR’s low resistance permits excitation with a large current at a low driving voltage, like the mag­netic dipole, and increases the radiation efficiency. The authors present the results of theo­retical and experimental investigations to illustrate the concept of improved LCR designs.

Chapter 11, “Novelda Nanoscale Impulse Radar,” by James D. Taylor and Dag T. Wisland, CEO of Novelda AS, Norway, gives a technical description of the Novelda Nanoscale impulse radar. All major electronic components of the Novelda radar fit on a 2 × 2 mm CMOS chip. The radar has a range of 60 m and uses a novel continuous time binary val­ued signal acquisition to detect radar returns and provide a digital signal return value for each of 512 range bins. Signal detection uses swept threshold and stochastic resonance sampling to increase the signal-to-noise ratio. The descriptions of the signal detection and signal-to-noise improvement features demonstrate new approaches to impulse radar design. Novelda AS can provide a complete development kit with a radar with antennas and a computer interface to help potential users develop special applications.

Chapter 12, “Principles and Methods of Material-Penetrating UWB Radar Imagery,” by Anatoliy Boryssenko and Elen Boryssenko of A&E Partnership, Belchertown, Massachusetts, presents the key operational principles and design concepts of material-penetrating UWB radars and imaging. The authors place special emphasis on system-level analysis and implementation issues for the major radar building blocks. They cover imag­ing techniques with synthetic and physical apertures. The results of several real-world projects from the authors’ consulting practice illustrate the principles.

Chapter 13, “Holographic Subsurface Radar Technology and Applications,” by Sergey I. Ivashov, Lorenzo Capineri, and Timothy D. Bechtel, describes how holographic subsur­face radar (HSR) differs from the two other types of GPR by providing plan-view sub­surface images or radar holograms. In this sense, HSR uses signal-processing methods analogous to the optical hologram technology first proposed and accomplished by D. Gabor in 1948. The authors describe the development of a holographic imaging radar and the results of tests performed during renovations of old buildings.

Chapter 14, “Xaver™ Through-Wall UWB Radar Design Study,” by James D. Taylor with Eyal Hochdorf, Jacob Oaknin, Ron Daisy, and Amir Beeri of Camero, Inc., presents a case study in through-wall radar (TWR) design. Several companies have built and marketed TWR systems for police, military, and emergency responders. This chapter discusses the TWR operational problem by examining the design constraints and showing state-of-the-art systems. The case study shows how Camero, Inc., engineers developed systems that can present the operator a three-dimensional (3D) picture showing the occupants and con­tents of a room through a reinforced concrete wall. Examples of Xaver™800 TWR high-resolution imaging show the results of the advanced design concepts.

Chapter 15, “The Camero, Inc., Radar Signal Acquisition System for Signal-to-Noise Improvement,” by James D. Taylor with Eyal Hochdorf, Amir Beeri, and Ron Daisy, exam­ines a new concept in signal-to-noise ratio (SNR) improvement. Camero, Inc., engineers found a major problem of low signal return levels, which limited through-wall imaging radar systems. While building the Xaver™ 400 and 800 series of through-wall radars, they wanted to improve the return SNR from all ranges to provide high-quality imaging over the full operational range. This chapter summarizes the Camero, Inc., Patent US 7,773,031 B2 August 10, 2010 “Signal Acquisition System and Method for Ultra-Wideband (UWB) Radar” invented by Camero engineers Amir Beeri and Ron Daisy in Kfar Netter, Israel. The patent describes a way to collect range information from a series of discrete ranges, store the return signals from multiple pulses in range cells, and integrate them to improve the SNR. The system can vary the number of integrations according to the range to achieve high SNRs across the entire operating range.

Chapter 16, “The Camero, Inc., Time Delay Calibration System for Range Cell Synchronization,” by James D. Taylor with Eyal Hochdorf and Nimrod Shani, examines the problems of aligning range cells from a multiple transmitter and receiver imaging radar antenna array. Multiple-channel UWB radars for high-resolution imaging require an exact alignment of range cell data collected from each channel. Xaver, Inc., engineers developed a self-calibrating system that can measure the time delays produced by trans­mitters and receivers and by physical displacement of antenna array elements. This time delay calibration system (TDCS) applies these delay measurements to each transmitter–receiver channel to synchronize multiple range cell data arrays. This patented approach has valuable implications for building multiple-element high-resolution radar systems.

Chapter 17, “The Camero, Inc., UWB Radar for Concealed Weapons Detection,” by James D. Taylor and Eyal Hochdorf, surveys the state of the art in security screening systems. Camero, Inc., developed and demonstrated a UWB imaging radar to scan people passing through a security screening area. This radar can detect concealed weapons, explosives, and contraband materials through clothing. Although other companies have tried X-ray and millimeter wave (MMW) imaging backscatter techniques, none have used the real time high-resolution imaging capabilities of UWB radars as a screening system for air­ports, public buildings, and other high-security areas.

Caveat and Invitation

UWB radar technology will continue to evolve in the future, but the principles will remain the same. You will find explanations of UWB radar theory and practice in the following pages. Books can only show the latest knowledge at the time of publication. In 1775, Samuel Johnson, compiler of the Dictionary of the English Language, responded to his critics by saying, “Dictionaries are like watches: the worst is better than none, and the best cannot be expected to go quite true.” Please exercise your judgment when you use this guide to new ideas and uncharted territory. If you wish to participate in forthcoming books on UWB radars, please feel free to contact me through the publisher with ideas for the next book in this series.

James D. Taylor

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