Radar Fundamentals

Overview

Radar is a critical element of many surveillance systems that prevail in today’s military and civilian environments. Its role in these environments includes target detection and identification, navigation and mapping, target tracking and weapons guidance. Modern radar is capable of extracting surprisingly accurate parametric information about its targets including range, bearing, velocity, configuration and identity.

This text covers the basics of radar operations and theory, provides a background into the many radar-related areas and covers the electronic warfare (EW) issues from a radar perspective. Introduction of important radar principles is combined with an explanation of the major types of radar wherever possible so that the reader becomes familiar with the principles and radar types simultaneously.

The text is specifically designed for non-technical people who require an understanding of the most important radar principles, or people with a technical background looking for a broad introduction to radar systems. Accordingly, the text avoids as much as possible of the mathematical complexity inherent in the subject. Those with a more technical bent can delve further into the subject by referring to the endnotes listed at the end of each chapter.

Preface

Radar is a critical element of many surveillance systems that exist in modern military and civilian environments where its roles include target detection and identification, navigation and mapping, target tracking and weapons guidance. Modern radar is capable of extracting surprisingly accurate parametric information about targets including range, bearing, velocity, configuration and identity. Although radar is an applied electrical engineering discipline involving complex mathematical concepts and theories, it is also a physical technology bounded by well-established laws of physics and nature. Consequently, a majority of radar concepts can be explained without the complexity. That is the primary aim of this text.

This text covers the basics of radar operations and theory, provides a background into the many radar-related areas and covers the electronic warfare issues from a radar perspective. Introduction of important radar principles is combined with an explanation of the major types of radar wherever possible so that the reader becomes familiar with the principles and radar types simultaneously. We do not attempt to study specific radar systems in any depth although some example systems are discussed to reinforce theory and concepts. We also avoid some of the more complex radar topics such as antenna design, transmission systems and receiver and transmitter electronics. The text is specifically designed for non-technical people who require an understanding of the most important radar principles, or people with a technical background looking for a broad introduction to radar systems. Accordingly, we avoid as much as possible of the mathematical complexity inherent in the subject. Some mathematics is unavoidable and is used to explain important principles. Those with a more technical bent can delve further into the subject by referring to the endnotes listed at the end of each chapter.

Specifically, this text has been developed to provide basic radar system knowledge to radar operators or those employed within radar environments. The text also supports other persons in radar-related endeavours such as the acquisition or maintenance of radar systems.

The text is divided broadly into five parts: radar basics, Doppler radars, high-resolution radars, the radar operating environment, and radar electronic warfare.

The first part commences with an introduction to the principles behind radar operation and explains the main types of radar systems. In Chapter 1, a basic radar block diagram is introduced to familiarise readers with the major components of a radar system. The important relationship between frequency and wavelength is also reinforced prior to any detailed coverage.

In Chapter 2, the reader is introduced to basic pulse radar as a means of explaining some fundamental radar concepts. The first concept is the ability of a radar system to determine the distance to a target. This leads to the concepts of pulse repetition interval, pulse repetition frequency, and pulse width, and the associated problems of range ambiguity, range resolution and blind range.

The concepts behind radar antennas are then discussed in Chapter 3. The coverage concentrates on basic parabolic reflectors and an introduction to phased array antennas. The antenna concepts of beamwidth, gain, polarisation and sidelobes are explained.

Chapter 4 describes a subset of the many radar displays in existence with operation radar systems. The chapter also describes radar’s role in the broader context as a sensor within a larger system. The interfaces between radar systems and operational environments including aircraft, ships and air traffic control environments are described.

The ubiquitous radar range equation is discussed in Chapter 5 as an excellent guide to radar performance and the many tradeoffs that exist in radar design. The equation is derived from first principles and shown in some of its many different forms. The concepts of transmitted power, minimum detectable signal strength, and radar cross section are introduced and related to radar range performance in the chapter. Pulse integration is also explained as a means of improving radar performance.

The second part of the text deals with radars that make use of the Doppler effect. Chapter 6 describes the Doppler effect, which is a well-known acoustic effect widely used in continuous wave radar. A variant of continuous wave radar called frequency-modulated continuous wave radar is introduced in Chapter 7. Pulse Doppler radar and, in particular, moving target indication radar, is described in Chapter 8 as the final example of radars that make use of the Doppler effect. The techniques of pulse Doppler and moving target indication combine the power of pulse radar and continuous wave radar to enhance the performance of a radar system. The concept known as Doppler blind speed is explained and calculated.

Part three of the text investigates high-resolution radar and starts with an investigation of tracking radar in Chapter 9. Lobing and scanning are explained as are the concepts of monopulse tracking, and range and velocity tracking. Pulse compression techniques are becoming widely used in modern radar systems due to the recent explosion in available signal processing power. Chapter 10 provides a qualitative coverage of pulse compression and demonstrates the power behind the principle and its ability to produce high resolution in range measurement. Synthetic aperture radar makes use of signal processing to synthesise extremely large antenna apertures and produces extremely high angular resolutions. SAR, and a closely related topic called inverse synthetic aperture radar is discussed in Chapter 11. Secondary surveillance radar is considered a combined radar and communications system, which is explained in Chapter 12 as providing detailed information about a target’s identity and location.

The radar’s operating environment is described in the fourth part of the text. Chapter 13 begins with a broad coverage of the many electromagnetic propagation issues relating to radar systems are explained. Issues such as scattering, refraction, attenuation and external noise are covered concentrating on how these issues may constrain the selection of a suitable operating frequency. Radar clutter is described in Chapter 14 as a major issue affecting the operation of radar in a real environment. The concept of radar cross section density is introduced as a way of calculating the signal-to-clutter ratio for a given radar and determining its likely performance impacts. Sea clutter and land clutter are discussed as are techniques for detecting targets in a cluttered environment. Some of the most common design concepts employed by radar designers to counter the operating environment are described in Chapter 15 and their operation is qualitatively described. The principles of fast time constant, sensitivity time control and instantaneous automatic gain control are included.

The final part of the text covers the electronic warfare aspects of radar operation and breaks electronic warfare into the traditional three components; electronic support, electronic attack and electronic protection. Electronic support and the techniques employed to intercept and analyse radar energy are discussed in Chapter 16. The electronic support chapter covers the aims of electronic support and then discusses electronic support systems in terms of antennas, receivers and displays. The concept of probability of intercepting radar energy is discussed to illustrate the challenges associated with successful electronic support. Electronic attack techniques aim to deny enemy use of the radar spectrum. The major electronic attack tactics are described and discussed in Chapter 17 and then the major tools are described. These tools include chaff, decoys, jamming, vehicle design and anti-radiation missiles. Jammer-to-signal strength is discussed and the concept of "burnthrough" is explained. Electronic protection involves using radar systems successfully in the presence of enemy electronic attack and is detailed in the final chapter, Chapter 18. The concept of "burnthrough" is revisited to illustrate radar design that can be used as an effective electronic protection. Electronic protection is then covered in terms of antenna, transmitter, and receiver design.

At the end of each chapter is a list of reference material that readers may use to explore each topic in more detail. A set of review questions is also provided at the end of each chapter with the answers to quantitative questions provided in brackets.

Three appendices are provided to support the text. Appendix A lists and expands the acronyms that are used throughout the text and dominate the radar discipline. Appendix B provides a list of common prefixes and the Greek alphabet and Appendix C explains the decibel as applied to radar systems.

Table of contents

CONTENTS
1	INTRODUCTION	1
1.1	Basic Radar Operation	1
1.2	Basic Radar Types	3
1.3	Electromagnetic Propagation Fundamentals	5
1.4	Radar Band Designation	8
1.5	Electronic Warfare Taxonomy	8
2	PULSE RADAR CONCEPTS	9
2.1	Pulse Radar Block Diagram	9
2.2	Range-Related Calculations	14
2.3	Normal Pulse Radar Operation	17
2.4	Pulse Width and PRF Considerations	18
2.5	Summary	30
3	BASIC RADAR ANTENNAS	27
3.1	Major Antenna Types	27
3.2	Antenna Characteristics	29
3.3	Electronically Steered Planar Arrays	53
3.4	Summary	70
4	RADAR DISPLAYS AND INTERFACES	61
4.1	Radar Displays	61
4.2	Radar Interfaces	64
5	RADAR RANGE EQUATION	71
5.1	Derivation of the RRE	71
5.2	Minimum Detectable Signal Strength	73
5.3	Pulse Integration	75
5.4	System Losses	79
5.5	Radar Cross-Section	80
5.6	COSEC2 Revisited	83
5.7	Examples and Calculations	85
5.8	One-Way Radar Range Equation	88
5.9	Summary	89
6	CONTINUOUS WAVE RADAR	89
6.1	Doppler Effect	s89
6.2	CW Radar Block Diagram	90
6.3	CW Radar Characteristics	93
6.4	Summary	96
7	FREQUENCY-MODULATED CW RADAR	97
7.1	FM CW Block Diagram	97
7.2	FM CW Characteristics	102
8	PULSE DOPPLER RADAR	109
8.1	Pulse Doppler Radar Concepts 109
8.2	Moving Target indication	111
9	TRACKING RADAR TECHNIQUES	119
9.1	Target Acquisition	119
9.2	Tracking Radar	120
9.3	Other Tracking Radar Concepts	131
9.4	Summary	134
10	PULSE COMPRESSION	133
10.1	Concept of Operation	133
10.2	Revised Radar Range Equation	139
10.3	Range Resolution	140
10.4	Minimum or Blind Range	141
10.5	Design Considerations	142
10.6	Worked Example	144
10.7	Summary	145
11	SYNTHETIC APERTURE RADAR	145
11.1	SAR Concepts	146
11.2	Unfocussed SAR	148
11.3	Focussed SAR	154
11.4	Design Issues	156
11.5	Inverse SAR	160
11.6	Summary	163
12	SECONDARY SURVEILLANCE RADAR	163
12.1	Civilian Air Traffic Control Applications	164
12.2	Military Applications	164
12.3	SSR Antennas	165
13	THE NATURAL ENVIRONMENT	169
13.1	Reflection From the Earth’s Surface	169
13.2	Refraction	173
13.3	Attenuation	176
13.4	External Noise	179
13.5	Summary	180
14	CLUTTER	181
14.1	Clutter Calculations	181
14.2	Clutter Description	185
14.3	Detecting Targets in Clutter	187
14.4	Summary	188
15	RADAR RECEIVER TECHNIQUES	189
15.1	Sensitivity Time Control (STC)	189
15.2	Instant Automatic Gain Control (IAGC)	191
15.3	Logarithmic-Fast Time Constant (Log-FTC)	194
16	ELECTRONIC SUPPORT	199
16.1	The Need for ES	199
16.2	The ES Process	200
16.3	ES Equipment	208
16.4	Challenges of ES – Probability of Intercept	217
16.5	Summary	223
17	ELECTRONIC ATTACK	221
17.1	EA Process	221
17.2	EA Tactics	222
17.3	EA Tools and Techniques	224
17.4	Summary	248
18	ELECTRONIC PROTECTION	243
18.1	Burnthrough Revisited	243
18.2	Radar's Inherent EP	244
18.3	Antenna Design Considerations	246
18.4	Transmitter Design Considerations	254
18.5	Receiver Design Considerations	261
18.6	Summary	264
APPENDICES
A	ACRONYMS	263
B	COMMON PREFIXES AND THE GREEK ALPHABET	267
C	DECIBELS	269
	INDEX	271

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