Matlab在雷达信号处理中的实用指南

matlab

信号处理

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CHAPTER 1

Introduction

This chapter enables the reader to:

•

Know the content and organization of this book, and how to use it to analyze

and model radar system performance;

•

Understand the concept of radar operation, the functions performed by radar,

and how radar may be used in various applications;

•

Understand the characteristics of functional radar models and how they are

used to analyze overall radar performance.

Radars are increasingly being used as integral parts of complex systems. Exam

ples include air-traffic control systems, ballistic-missile defense systems, air-defense

systems, and targeting systems for land attack. Analysis of radar in such systems

requires representing the radar operation and performance in the context of the

overall system and the external environment. The radar performance must be evalu-

ated in performing system tasks, and the impact of radar operation on system per-

formance must be quantified.

Analysis of such systems may use a variety of tools, ranging from simple off-line

calculations of radar performance to complex computer simulations of overall sys-

tem operation. Models of radar operation and performance are needed for these

system-level analyses. The radar representations in these models must be responsive

to the to the key radar characteristics, system interfaces, and performance measures.

However, they should be simple enough to allow their use in large-scale system

simulations, and to represent radar whose detailed design is not fully known. Radar

simulations used for detailed radar design and analysis are generally too complex

for such system-level analysis.

1.1 This Book and How to Use It

This book addresses the needs of system analysts for radar models and analysis

tools. It describes the basic principles of radar operation, how radar is configured

and used in military and civilian systems, and how to analyze and model radar at the

system level. The book presents and explains equations, computational methods,

and data, and provides insight on how to use the models in system analysis. The

book may serve both as a text for learning radar system performance analysis and

modeling, and as a reference for engineers and modelers working in the field.

System-level radar modeling requirements are different from radar design mod

els requirements. The latter involve details of the radar hardware and trace the sig

nals through the various elements of the radar. They focus on how to make the radar

work. System models, on the other hand, focus on overall radar performance, and

often rely on basic principles. Thus, they may be used for conceptual radar that has

not been fully designed or built, or for parametric analyses of radar designs. They

usually assume the radar has been, or will be, designed to work properly. These

models represent the key features of radar without excessive detail.

The radar models described in this book may be used by system analysts to

evaluate systems that include radar, and by modelers and programmers involved in

simulating the performance of radar in systems. Several of the key models are pro

grammed into custom radar functions, so that the models may be readily used for

radar analysis in Excel workbooks. These may also provide a guide for modelers and

simulation programmers.

This book is intended for engineers who are evaluating radar system issues, sys

tems analysts who are involved with systems that include radar, and programmers

who are simulating the performance of radar. It is aimed at engineers, scientists, and

mathematicians who are not radar experts. Only a general engineering and mathe

matical background is assumed; no specialized radar engineering or advanced

mathematics is required. In developing and describing the models, the book gives the

reader a basic understanding of radar principles.

This chapter provides a brief an overview of radar operation and applications,

followed by a discussion of functional radar models and their software representa-

tions. Chapters 2, 3, and 4 discuss radar configurations, radar parameters and radar

waveform characteristics. These provide a general radar understanding for the sys-

tems analyst, to serve as background for radar analysis and model development.

These chapters may be skipped by those already familiar with basic radar principles,

or may be used as reference material.

The radar models are developed and presented in Chapters 5 through 11. In

these chapters, the reader may go directly to modeling topics of interest. References

are made to discussions and results in other chapters, where they are helpful to

understanding the material. The final section in each of these chapters describes the

Excel custom radar functions that are based on the chapter topics. Analysis exam

ples using the radar models together to solve practical radar problems, both analyti

cally and in Excel workbooks, are given in Chapter 12.

Most of the models in this book may be found in, or derived from, material in

standard radar texts [1–3]. The book collects the radar material needed by system

modelers, presents it in a concise format, and provides guidance for using it in sys

tems analysis. Selected bibliographies are provided at the end of each chapter that

give sources of additional background and information on the topics addressed in

the chapter. They are intended to enrich the reader’s knowledge of radar and pro

vide information that goes beyond the scope of this book.A list of symbols used in

the book, along with their definitions, is given in Appendix A. Appendix B contains

a glossary of key terms and acronyms used in the book. A list of the custom radar

functions with directions for their installation and use is provided in Appendix C.

Appendix D gives procedures for converting the standard metric units used in the

models in this book to and from various measurement units (see Section 1.4).

2 Introduction

Practice problems are provided for each chapter, to assist in reviewing the les

son material, and to ensure an understanding of it. These problems may be solved

using the methods, equations, and data in this book. Solutions to these problems

appear in Appendix E.

A self-test that covers the material presented in this book is provided in Appen

dix F. This test may be used to evaluate comprehension of the material in the book.

Answers to the test questions are provided at the end of the appendix.

1.2 Concept of Radar Operation

Radar stands for RAdio Detection And Ranging. The basic radar concept is that

radio frequency (RF) energy is generated by the transmitter, radiated by the trans

mitting antenna, reflected by the target, collected by the receiving antenna, and

detected in the radar receiver. This is illustrated in Figure 1.1. In practice, many

radars use the same antenna for both transmitting and receiving.

Since the electromagnetic energy travels with the speed of light (designated c),

the range from the radar to the target, R, may be determined by measuring the time

interval, t, between the transmitted signal and the received signal:

(1.1)

The electromagnetic propagation velocity in the atmosphere is nearly the same

as that in a vacuum, and the approximation c = 3 × 10

m/s is sufficiently accurate

for most analyses.

The direction of the target relative to the radar may be determined by using an

antenna with a directional pattern, and observing the direction from which the peak

of this pattern is pointing when the received signal is maximized.

The target radial velocity, V

, is the component of target velocity in the direction

of the radar. This may be found from the range changes for successive radar meas

urements, or from the Doppler-frequency shift of the return signal. The frequency of

the electromagnetic signal that is reflected from a target that is moving either toward

or away from the radar is changed. The target velocity component in the direction of

the radar is proportional to this Doppler-frequency shift, f

, of the received signal:

(1.2)

1.2 Concept of Radar Operation 3

Transmitter

Receiver

Target

velocity

Radial

velocity

Target

data

Range

Synchronization

Figure 1.1 Concept of radar operation.

•

Cued search, where a target location is approximately known, and a small

volume around the estimated position (the cue), is searched.

•

Push-broom search, where a moving radar (e.g., on an aircraft), searches the

volume as it moves along its path. This is similar to barrier search, but the bar

rier moves with the radar platform.

Modeling of radar search modes is addressed in Chapter 7.

Radar detection is the determination that a target is present in the search vol

ume. This is usually accomplished by setting a received-signal threshold that

excludes most noise and other interfering signals. Signals that exceed this threshold

are the detected targets. Since radar background noise and many target signals fluc

tuate, detection is a statistical process. It is usually characterized by a probability of

detection, P

, and a probability of false alarm (false detection), P

[1, pp. 23–25].

Modeling of radar detection is discussed in Chapter 6.

The radar measures target position in range and angular coordinates, as dis

cussed in Section 1.2. Radar tracking is the determination of the path of a moving

target from a series of position measurements. In its simplest form, this is simply

associating successive measurements with a target and connecting them. Better

tracking performance is obtained by using a tracking filter, which smoothes the

position measurements, and estimates the target trajectory parameters. When tar-

gets can maneuver, the degree of smoothing employed in the tracking filter is a com-

promise between improving the track accuracy and following the target maneuvers.

Models for radar measurement and tracking are discussed in Chapter 8.

A radar may measure other target features in order to better characterize or

identify the target, as discussed in Section 8.4. These measures may include RCS

(discussed in Sections 1.2 and 3.5); fluctuations of RCS with time, target size, target

shape and configuration (using imaging radar – discussed in Section 2.5); and target

motion characteristics shown by the Doppler-frequency spectrum of the received

signal.

1.4 Functional Models

The radar models presented in this book are termed functional models. This implies

that they are generally not intended to simulate details of radar hardware design,

electromagnetic propagation, and statistical methods. Rather, the models represent

the effects of these characteristics on the overall performance of the radar. In order

to apply to a wide range of radar situations, these models are often based on physi

cal principles, rather than details of specific radar designs.

In order to maintain reasonable fidelity while using such simplifications, the

models use the key parameters that impact specific results. For example, the radar

antenna, (discussed in Section 3.2), requires a number of parameters for complete

characterization. However, only the transmit gain, the receive aperture area, and

the antenna losses impact the radar sensitivity as measured by the signal-to-noise

ratio (S/N). These parameters are used in the models for S/N in Chapter 5. On the

other hand, the antenna beamwidth is the key antenna parameter for calculating the

radar angular measurement accuracy in Section 8.2, and the antenna sidelobe level

1.4 Functional Models 5

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