Radar and Electronic Warfare Principles for the Non-specialist
Many readers will recognize the previous editions of this book covering the essentials of radar, but this new edition now includes the fundamentals of electronic warfare (EW) as well. This book distills the very complex, rich technologies of radar and EW into its fundamentals, tying them to the laws of nature on one end and to the most modern and complex systems on the other. This should be the first book selected to provide a solid foundation in both radar and electronic warfare. Readers with a technical or business degree should be well prepared to understand the vast majority of concepts in this book as they are mathematically represented using algebra. Some concepts use trigonometry and a very select few use calculus. It is written specifically for those with little or no knowledge of radar and EW technologies.
Other keywords: radar antenna; target detection; target signature; electronic warfare receiver; self-protection jamming electronic attack; radar measurement; target tracking
- Book DOI: 10.1049/SBRA502E
- Chapter DOI: 10.1049/SBRA502E
- ISBN: 9781613530115
- e-ISBN: 9781613530306
- Page count: 425
- Format: PDF
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Front Matter
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1 Introduction to Radar and Electronic Warfare
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This chapter discussed the introduction to radar systems and the target signature and the introduction to electronic warfare.
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2 Radar Systems
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Radar is an acronym for “RAdio Detection And Ranging.”A radar system detects the presence of objects in the environment and measures characteristics of the object: range, range rate, and angle. A radar system works by sending out (transmitting) radio frequency (RF) waves and collecting (receiving) the signals that reflect from objects in the environment. Reflection is the reradiating (scattering) of the incident RF wave from the object. Objects the radar is designed to detect are called “targets,”while all other objects are called “clutter.”Before I develop the principles of radar, I will review the characteristics of RF waves the basis of radar systems.
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3 Target Detection
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Detection theory is often one of the most confusing radar system topics. Hopefully, this chapter clearly addressed detection theory, threshold detection based on Pd and Pfa, multiple-pulse integration, fluctuating target RCS, and additional detection techniques. Target detection is based on probability theory. We developed the concepts and math radar system behind Pfa and Pd, starting with the basics of a constant amplitude target signal and continuing to the Swerling fluctuating target RCS cases. We also saw how integrating multiple pulses can greatly improve a radar system's detection performance (i.e., Pd, Pfa, and detection range). Radar engineers use detection theory to understand the relationships between the detection threshold, Pfa, FAR, Tfa, Pd, integration time, number of pulses integrated, coherent pulses, and noncoherent pulses. There are many ways to obtain a desired detection performance. As we will discuss in Chapter 5, target measurement and tracking capability and performance are also a function of the characteristics of the radar system. Radar engineers knowledgeably balance these interrelationships to ensure the radar system has the required detection, measurement, and tracking capability and performance. Radar is one big systems engineering problem.
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4 Radar Antennas
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All radar antenna types-reflectors, arrays, or reflectors illuminated by an array-have the same end result: an antenna gain pattern. The antenna gain pattern is the antenna gain as a function of angle: azimuth, elevation, or offaxis. Thus, the antenna gain is not a single value. All radar antennas can be characterized by their mainbeam (maximum) gain, beamwidth, and sidelobe levels. These antenna characteristics are a function of frequency, current distribution, and antenna physical dimensions. Many antenna rules-of-thumb are left over from the dark ages of calculation. Fortunately, many of them have disappeared over time, but some still exist, either explicitly or embedded into other areas of radar and the associated equations. Therefore, it is important to be careful about applying them in a particular situation.
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5 Radar Measurements and Target Tracking
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A measurement is a characteristic of a detected target as determined by the radar system: range, range rate, azimuth angle, and elevation angle. Radar systems are often categorized based on the number or type of measurements they provide. Two-dimensional (2D) radar systems provide range or range rate and one angle (azimuth or elevation). Three-dimensional (3D) radar systems provide range or range rate, azimuth angle, and elevation angle. Target tracking is the following of a time sequence of target measurements. The time sequence of measurements can be continuous for a target tracking radar system. Target tracking radar systems use measurement trackers to independently track in range, range rate, and angle. The time sequence of measurements can be near-continuous for a track-while-scan radar system. For a search radar system the scan period determines the time sequence of target measurements.
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6 Target Signature
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The signature of a target is defined by its radar cross section and spectrum. The RCS determines the amplitude component, and the spectrum determines the frequency domain component of the received target signal power. Target RCS is complex, both electromagnetically and mathematically. The RCS of a target is a function of both target characteristics (i.e., size, shape, materials) and radar characteristics (i.e., frequency, polarization). We often simplify target RCS by looking at simple geometric shapes when possible. The RCS of complex shapes, the targets in which we are most interested, is the complex (amplitude and phase) combination of the scattering off all parts of the target. We often visualize the RCS of complex targets with plots as a function of azimuth angle, elevation angle, frequency, and polarization. The RCS of complex targets is not a single value. It has a very wide range of values-often several orders of magnitude (powers of 10). For Doppler radar systems the target's spectrum needs to be considered along with the RCS.
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7 Advanced Radar Concepts
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Radar systems are pervasive in modern life. Military applications include all of those previously mentioned plus enormously varied additional uses associated with the military missions, such as surveillance, reconnaissance, targeting, and weapons delivery-on land, at sea, and in aerospace. Although military applications dominate, at least as far as big complex radar systems are concerned, nonmilitary applications are legion. Many medium-sized private boats and airplanes are radar equipped, the former for navigation and the latter for obtaining accurate altitude. Commercial airlines and ships are almost all radar equipped. In law enforcement, traffic and border patrol officers often employ radar systems. The Federal Aviation Agency (FAA) operates at least 40 large radar systems and numerous small ones to keep track of the nation's air traffic, with the higher altitudes being under radar control at all times. Many companies and individuals with high-value facilities use radar systems for security.
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8 Electronic Warfare Overview
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Because radar systems find and make measurements of noncooperative targets, it motivates various countering actions. Motorists might want to deprive the highway patrolman of information about their speed to avoid a ticket. Certainly, nations want to deny other nations all kinds of information, particularly in times of tension or war. Electronic warfare (EW) seeks to deny, degrade, and/or deceive an adversary's radar systems to ensure successful completion of the friendly force's mission [see the numerous references at the end of this chapter]. EW is divided into three components: electronic support (ES), electronic attack (EA), and electronic protection (EP). The purpose of ES is to intercept, identify, and locate radar systems. The purpose of EA is to “attack”radar systems to negatively affect their performance and/or capability. The purpose of EP is to protect radar systems from ES or EA. Traditionally, ES has been known as electronic support measures (ESM), EA has been known as electronic countermeasures (ECM), and EP has been known as electronic countercountermeasures (ECCM). An international professional EW society called the Association of Old Crows (AOC) advances strategy, policy, and programs for EW and electromagnetic spectrum operations. Since the fate of nations may depend on the effectiveness of ES, EA, and EP, details related to specific EW concepts and systems are highly classified. However, many useful general principles of ES, EA, and EP can be discussed and quantified.
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9 Electronic Warfare Receivers
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Electronic warfare (EW) receivers-radar warning receivers and jammer receiver processors-are an element of Electronic Support (ES). EW receivers provide situational awareness (SA) about radar systems and other emitters (e.g., radios, data links) in the radio frequency (RF) environment [Neri, 2006, Chapter 4; Schleher, 1999, Chapter 6]. An EW receiver uses sensitive receivers to collect radar waveforms from the RF environment. It then detects radar signals in the presence of EW receiver thermal noise. Signal processors extract parameters from the detected radar signals and use them to identify specific radar systems and determine their location. The challenge for an EW receiver is to do all this quickly in a dense RF environments, millions of radar pulses per second and background (e.g., TV, radio, cell phone) emitters, at operationally useful ranges. The fundamental goal of all EW receivers is to “see them (radar systems) well before they see you (the platform with the EW receiver).
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10 Self-Protection Jamming Electronic Attack
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This chapter discussed self-protection jamming and developed the fundamental on-board self-protection jamming equation. We examined noise (wideband random amplitude and phase) self-protection jamming, false target (radar-like waveform) self-protection jamming, and expendable self-protection jamming (passive and active), their effects on the radar, and the metrics used to describe their performance. We concluded by looking at other self-protection jamming techniques used to deceive target tracking radar systems. Of course, the radar community does not sit idly by while the EW community renders its radar system useless. Numerous EP techniques have been developed in an attempt to preserve the radar system's target detection, measurement, and tracking capability and performance in the presence of EA. EP techniques are discussed in detail in Chapter 12.
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11 Support Jamming Electronic Attack
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In this chapter we will discuss support jamming principles along with the supporting math [Chrzanowski, 1990; Neri, 2006, Chapter 5; Schleher, 1999; Chapter 4; Van Brunt, 1978]. The effect of the support jamming is to obscure true target signals or introduce false targets. A successful support jammer does this over a wide angular extent about the radar system. The support jamming waveform most often enters the radar antenna through a sidelobe as the radar system is attempting to detect the targets through its mainbeam, as shown in Figure 11-1. Support jamming requires sufficient incident jammer power density to overcome the low radar antenna sidelobe gain. Sufficient incident jammer power density is obtained with a high jammer effective radiated power (ERP) and/or a short radar-to-jammer range. High jammer ERP is obtained either with a high power transmitter or a high gain antenna on the jammer that then must be steered at the radar or a combination of both.
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12 Electronic Protection Concepts
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In this chapter we will describe three EP concepts in more detail: radar waveform diversity and low probability of intercept; antenna-based signal processing; and sophisticated target trackers.
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13 Loose Ends of Radar and/or Electronic Warfare Lore
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Several other brief quantitative notions and a list of rules-of-thumb should be included in any set of radar and electronic warfare (EW) fundamentals. Some are good for general day-to-day use; others are important to detailed radar and/or EW design calculations. They are pulled together in this chapter without concern for their relevance to each other but only because they are valid radar and EW lore.
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Appendix 1: Decibels
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Bels were named after Alexander Graham Bell. They were simply the logarithm of the ratio of power out and power in. The definition of a decibel (dB) is contained in any radio engineer's handbook, as given as follows. Since radar and electronic warfare engineers use power, the 10log10(x) from is by far the most common. In colloquial usage, decibels are used to express any ratio or often just an absolute value. Decibels are just 10 times the 1og10 of the ratio or value. A factor of two results in about 3 dB, while a factor of one half results in about -3 dB of magnitude (powers of 10) are represented by “only”120 dB. After working with dB values a while, they are usually memorized by radar and EW people.
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Appendix 2: The Radar Spectrum
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Appendix 3: Fourier Series and Transforms
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Working in the field of heat transfer in the early nineteenth century, Jean B. S. Fourier found that virtually all functions of time, particularly repetitive ones, could be described in a series of sine and cosine waves of various frequencies and amplitudes. His work has been described as one of the most elegant developments in modern mathematics. Whatever its stature for the world, the benefits for the radar engineer are epic. The following presentation uses the approach taken by H. H. Skilling in Electrical Engineering Circuits, Chapters 14-15 (New York: Wiley, 1957). George Stimson also has an excellent discussion on Fourier series and transforms in Introduction to Airborne Radar, 2nd edition, Chapters 17 and 20 (Raleigh, NC: SciTech, 1998).
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Appendix 4: Answers to Exercises
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Appendix 5: Glossary
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This glossary provides assistance in understanding terms used in this book. There may be more general, more specific, or entirely different meanings for these terms when they are used elsewhere. Some of the terms are: radar system; electronic attack; electronic countermeasures; electronic counter-countermeasures; electronic protection and electronic warfare.
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Index
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Supplementary material
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Instructor Resources for "Radar and Electronic Warfare Principles for the Non-specialist"
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An Instructor Pack is available for instructors who have adopted the book for a course. To request an Instructor Pack, please email [email protected], including details of your institution and the course you are teaching.
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