RADAR SYSTEM ENGINEERING

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RADAR SYSTEM ENGINEERING

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MASSACHUSETTS INSTITUTE OF TEC’H.VOLOGY

RADIATION LABORATORY SERIES

Board of Editors LOUISN. RIDENOUR, Editor-in-Chief GEORGEB. COLLINS, Deputy Editor-in-Chief

BRITTON CHANCE, S. A. GOUDSMT, R. G. HEIIB, HUBERT M. JAMES, JULIAN K. KNIPP, JAMES L. LAWSON, LEON B. LINFORD, CAROL G. MONTGOMERY, C. NEWTON, ALBERT

M. STONE, Louxs A. TUENER, GEORGE E. VALLEY, JR., HERBERT H. WHEATON

1. RADAR SYSTEM ENGINEEi+lxG-Ridenour 2. RADAR AIDS TO ~AVIGATIOX—Hall 3. RADAR BEAcoNs—Roberts

4. LoEAx—Pierce, McKewie, and Woodward 5. PULSE Generators—6?asoe and Lebacqz 6. MICROWAVE MAGNETRONS—COllinS

7. KLYSTRONS A?JD MICROWAVE TmoDEs-Hamilton, Knipp, and Kuper 8. PRINCIPLES OF MICROWAVE Cmmurrs-Montgomery, Dtcke, and Purcell 9. MICROWAVE TRANSMISSION CIrwuITs—Ragan

10. WAVEGUIDE HANDBOOK—MarCUrIitZ

11. TECHNIQUE OF ?YIICROWAVEME,4sumnmsw-Montgomery 12. MICROWAVE ANTENNA THEORY AND DEs~Gix-Siker 13. PROPAGATION OF SHORT RADIO WAvEs—Kew 14. MICROWAVE ~upLExErm+-Smulzin and Montgomery 15. CRYSTAL RECTIFIERS— Torrey and Whitmer 16. MICIIOWAVE !vfIxERs-Pound

17. COMPONENTS HANDBooK—Blackburn

18. VACUUM TUBE AMPLIFIERS—~’U@ and Wa!lman

19. wAvE~oR~s—Chance, Hughes, M ac.NTichol,.Sayre, and Williams 20. ELECTRONIC TIME Measurements—Chance, Hulsizer, .Wac.Yichol,

and Williams

21. ELECTRONIC I Ns’rRuhiENm-Greenwood, Holdam, and MacRae 22. CATIIODE RAY TUBE DIspLAYs—So12er, Starr, and Valley 23. .~lCRO WAVE REcE1vEIw— Van Voorhis

24. THRESHOLD SIGNALs—Lawson and Uhlenbeck

25. THEORY OF SERvoiuEcIIANIsivs-James, Nichols, and Phillips 26. RADAR SCANNERS AND RADOXES—CUdrJ, Karelitz, and Turner 27. COMPUTING KIECHANISMSAND LINnGm-&oboda

28. I NDEx—Henney

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RADAR SYSTEM

c1 ^P* ^~s,\NsT,rF ^c+

Edited by

JIJL Lu 1947 LOUIS N. RIDENOUR %?Fl@

PF(OFESSOFI OF PHYSICS UNIVERSITY OF PENNSYLVANIA

Fllis’r’ E1)[TION

.

IVEII’YORK AND LONDON

!JIcGRA W-HILL BOOK COMPANY, INC.

1947

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RADAP. SYSTEM ENGINEERING

COPYRIGHT, 1947, BY THE

J1cC,R,iW-HILL BOOK CoMP.iNY, INC.

PRINTELI IX THE UNITED STATES OF AM ERI(..<

Aulr!qhh rf?send ‘1’h is hook., or pert: ihrrrqf, ?na~j no! hereprod7wd in 07(v Jm-TII wilhottl permission oj

the publishers.

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THE MAPLE PRESS COMPANY, YORK, PA.

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RADAR SYSTEM ENGINEERING

EDITORIAL STAFF LouIs N. RIDENOUR

AVIS M. CLARKE

CONTRIBUTING AUTHORS L. Y. BEERS

B. Y. BOWDEN W. M. C.4DY R. E. CLAPP C,. B. COLLINS A. G. EMSLIE W. W. HANSEN L. J. HAWORTH R. G. HERB M. M. HUBBARD P. C. JACOBS M. H. JOHNSON W. H. JORDAN J. V. LEBACQZ F. B. LIXCOLX R. A. MCCONNELL

F. J. MEHRINGER R. D. O’XEAL C. F. J. OVERH.WE E. C. POLLARD E. M. PURCELL L. N. RIDENOUR

C. V. ROBINSON A. J. F. SIEGERT R. L. SIIWHEIMER D. C. SOPER G. F. TAPE L. A. TURNER M. G. WHITE A. E. WHITFORD J. M. WOLF C. L. ZIMIERMAN

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Foreword

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HE tremendous research and development effort that went into the development of radar and related techniques during World War II resulted not only in hundreds of radar sets for military (and some for possible peacetime) use but also in a great body of information and new techniques in the electronics and high-frequency fields. Because this basic material may be of great value to science and engineering, it seemed most important to publish it as soon as security permitted.

The Radiation Laboratory of MIT, which operated under the super- vision of the National Defense Research Committee, undertook the great task of preparing these volumes. The work described herein, however, is the collective result of work done at many laboratories, Army, Navy, university, and industrial, both in this country and in England, Canada, and other Dominions.

The Radiation Laboratory, once its proposals were approved and finances provided by the Office of Scientific Research and Development, chose Louis N. Ridenour as Editor-in-Chief to lead and direct the entire project. An editorial staff was then selected of those best qualified for this type of task. Finally the authors for the various volumes or chapters or sections were chosen from among those experts who were intimately familiar with the various fields, ,and who were able and willing to write the summaries of them. This entire staff agreed to remain at work at MIT for six months or more after the work of the Radiation Laboratory was complete. These volumes stand as a monument to this group.

These volumes serve as a memorial to the unnamed hundreds and thousands of other scientists, engineers, and others who actually carried on the research, development, and engineering work the results of which are herein described. There were so many involved in this work and they worked so closely together even though often in widely separated laboratories that it is impossible to name or even to know those who contributed to a particular idea or development. Only certain ones who wrote reports or articles have even been mentioned. But to all those who contributed in any way to this great cooperative development enterprise, both in this country and in England, these volumes are dedicated.

L. A. DUBRIDGE.

Yii

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Preface

T

HEearliest plans for the Radiation Laboratory Series, made in the fall of 1944, envisaged only books concerned with the basic microwave and electronic theory and techniques that had been so thoroughly developed during the wartime work on radar. These plans were laid aside for a time when it became clear in this country that several months of fighting remained in the European war.

When work on the Series was resumed in the early summer of 1945, the books planned, as before, dealt with basic matters and with techniques.

Every effort was made to point out the general applicability of the work reported and to avoid special emphasis on its application to radar, since radar itself was thought to have only a limited importance.

The end of the Pacific war made it possible to put more effort on the job of preparing the Series than had been available earlier. The books on theory and techniques having been planned as comprehensively as appeared to be worth while, the work was extended by the addition of five books concerned with radar and allied systems.

Of those five books, this is the only one that deals with radar itself.

One book takes up the use of radar in navigation, one concerns the design of radar scanners and radomes, one treats the design and construction of beacons, and one describes hyperbolic navigational systems—in particular Loran.

This book is intended to serve as a general treatise and reference book on the design of radar systems. No apology seems to be needed for the fact that it deals primarily-though by no means altogether-with microwave pulse radar. Thousands of times as much work has gone into pulse radar as into any other kind, and the overwhehning majority of this work has been concerned with microwave pulse radar. The superiority of microwaves for almost all radar purposes is now clear.

The first eight chapters of this book are intended to provide an introduction to the field of radar and a general approach to the problems of system design. Chapters 9 through 14 take up the leading design con- siderations for the various important components that make up a radar set. These chapters are so thorough in their treatment that Chap. 15, which gives two fairly detailed examples of actual system design, can be quite brief. Chapters 16 and 17 take up two new and important ancillary

ix

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x PREFACE

techniques that are not dealt with fully elsewhere in the Series: moving- target indication and the transmission of radar displays to a remote indicator by radio means.

For fuller information than can be found in this book on any detailed point of design, the reader is referred to one of the other books of the Series. In a sense, this book specializes to radar the techniques repotied more fully elsewhere in the Series.

Radar is a very simple subject, and no special mathematical, physical, or engineering background is needed to read and understand this book.

Because the book covers the entire field of effort of the Radiation Laboratory and the other wartime radar establishments, its contributing authors are more numerous than those listed for most other volumes of this series. I am especially grateful to L. J. Haworth and to E. M.

Purcell, whose contributions have been more extensive than those of other authors, and whose advice on editorial problems has often been extremely helpful. In addition to the authors already listed, whose names appear in the book in connection with the material they have written, I wish to thank the following men for their work in provid- ing essential background material that did not eventually find its way into the book: R. M. Alexander, A. H. Brown, J. F. Carlson, M. A.

Chaffee, L. M. Hollingsworth, E. L. Hudspeth, R. C. Spencer, and I. G.

Swope. Changing plans for the book also reduced the acknowledged contribution of E. C. Pollard far below the very considerable quantity of material he prepared.

I owe an apology to all the authors for the liberty I have often taken in altering their original text to fit the final framework of the book and my own ideas of style. Because most authors left the Labora- tory immediately on finishing their writing, and much of the editorial work had to be deferred until the book was substantially complete, it has not always been possible to adjust with the authors the alterations in their manuscripts that have seemed desirable to me.

The general acknowledgments I owe as Editor-in-Chief of the Series are set forth in the Series Index. In connection with the preparation of this book, however, it is a pleasure to thank Dr. B. ~. Bowden, of the British Air Commission, not only for his assistance as an author but also for his general comments on the book as a whole. I am grateful to Lois Capen for her work in following the preparation of illustrations, and to Phyllis Brown for general secretarial assistance.

LOUIS N. RIDENOUR.

CAMBRIDGE, MASS.

Jum, 1946

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101. What Radar Does. —Radar is an addition to man’s sensory equipment which affords genuinely new facilities. It enables a certain class of objects to be “seen” —that is, detected andlocated—at distances far beyond those at which they could be distinguished by the unaided eye. This ‘(seeing” is unimpaired by night, fog, cloud, smoke, and most other obstacles to ordinary vision. Radar further permits the measurement of the range of the objects it “sees” (this verb will hereafter be used without apologetic quotation marks) with a convenience and precision entirely unknown in the past. It can also measure the instantaneous speed of such an object toward or away from the observing station in a simple and natural way.

The superiority of radar to ordinary vision lies, then, in the greater distances at which seeing is possible with radar, in the ability of radar to work regardless of light condition and of obscuration of the object being seen, and in the unparalled ease with which target range and its rate of change can be measured. In certain other respects radar is definitely inferior to the eye. The detailed definition of the picture it offers is very much poorer than that afforded by the eye. Even the most advanced radar equipment can on] y show the gross outlines of a large object, such as a ship; the eye can—if it can see the ship at all—pick out fine details such as the rails on the deck and the number or character of the flags at the masthead. Because of this grossness of radar vision, the objects that can usefully be seen by radar are not as numerous as the objects that canabe distinguished by the eye. Radar is at its best in dealing with isolated targets located in a relatively featureless background, such as aircraft in the air, ships on the open sea, islands and coastlines, cities in a plain, and the like. Though modern high-definition radar does afford a fairly detailed presentation of such a complex target as a city viewed from the air (see, for example, Fig. 335), the radar picture of such a target is incomparably poorer in detail than a vertical photograph taken under favorable conditions would be.

One further property of radar is worth remarking: its freedom from difficulties of perspective, By suitable design of the equipment, the picture obtained from a radar set can be presented as a true plan view,

1

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SEC.12] HOW RADAR WORKS 3 the radar picture would have been unaffected while photography or ordinary vision would have been useless.

1.2. How Radar Works.—The coined word rodaris derived from the descriptive phrase “radio detection and ranging. ” Radar works by sending out radio waves from a transmitter powerful enough so that measurable amounts of radio energy will be reflected from the objects to beseenby theradar toaradio receiver usually located, for convenience, at the same site as the transmitter. The properties of the received echoes are used to form a picture or to determine certain properties of the objects that cause the echoes. Theradar transmitter may send out c-w signals, or frequency-modulated c-w signals, or signals modulated in other ways.

Many schemes based on transmissions of various sorts have been proposed and some of them have been used. Chapter 5 of this book treats the general radar problem, in which any scheme of transmitter modulation may be used, in a very fundamental and elegant way.

Despite the great number of ways in which a radar system can in principle be designed, one of these ways has been used to such an overwhelming degree that the whole of this book, with the exception of Chap.

5, is devoted to it. When radar is mentioned without qualification in this book, pulse radar will be meant. NTOapology for this specialization is needed. Thousands of times as much effort as that expended on all other forms of radar put together has gone into the remarkably swift development of pulse radar since its origin in the years just before World War II.

In pulse radar, the transmitter is modulated in such a way that it sends out very intense, very brief pulses of radio energy at intervals that are spaced rather far apart in terms of the duration of each pulse. During the waiting time of the transmitter between pulses, the receiver is active.

Echoes are received from the nearest objects soon after the transmission of the pulse, from objects farther away at a slightly later time, and so on.

When sufficient time has elapsed to allow for the reception of echoes from the most distant objects of interest, the transmitter is keyed again to send another very short pulse, and the cycle repeats. Since the radio waves used in radar are propagated with the speed of light, c, the delay between the transmission of a pulse and the reception of the echo from an object at range R will be

(1) the factor 2 entering because the distance to the target has to be traversed twice, once out and once back, Figure 1.2 shows schematically the principle of pulse radar.

The linear relation between delay time and range shown in Eq. (I) is

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4 IN TRODUC7”ION

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Target

[SEC.1.2

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Radar

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Target

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Radar

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Yz’o’ti’”e’

Target

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Radar

FIG.1.2.—Theprincipleof pulseradar. (a) Pulsehas just been emittedfrom radar aat. (b) Pulaereachestarget. (.) Scatteredenergy,eturnsfromtarget;transZnittedpul`e carrieOon, (d) Echo pulsereachesradar.

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SEC.1.2] HOW RADAR WORKS 5 theclue totheease tithwtich range can remeasured by radar. Range measurement is reduced to a measurement of time, and time can be measured perhaps more accurately than any other basic physical quantity. Because the velocity of light is high, the intervals of time that must be measured in radar are short. Numerically, the range corre- sponding to a given delay time is 164 yd for each microsecond elapsing between the transmission of the pulse and the reception of the echo. If it is desired to measure range to a precision of 5 yd, which is necessary in some applications of radar, time intervals must be measured with a

precision better than & psec. Modern electronic timing and display techniques have been developed to such a point that this can readily be done.

One of the simplest ways in which radar echo signals can be displayed is shown in Fig. 1.3. The beam of a cathode-ray tube is caused to begin a sweep from left to right across the face of the tube at the instant a pulse is sent from the transmitter. The beam is swept to the right at a uniform rate by means of a sawtooth waveform applied to the horizontal deflection plates of the CRT. The output signals of the radar receiver are applied to the vertical deflection plates. To ensure that the weakest signals that are at all detectable are not missed, the over-all gain of the receiver is high enough so that thermal noise originating in the receiver (Sec. 2.7) is perceptible on the display. The two signals that rise significantly above this noise in Fig. 1.3 are, on the left, the “tail” of the transmitted

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6 INTRODUCTION [SEC.1.3 pulse leaking into the receiver, and on the right, the echo signal from a radar target. The target in the particular case of Fig. 1“3 is the earth’s moon.

The measurement of range by means of radar is thus a straightforward problem of time measurement. It is also desirable to be able to measure the direction in which a target lies as viewed from a radar station. In principle, this can be done on the basis of triangulation, using range information on the same target from two or more separate radar locations.

Although this method permits of great accuracy and has occasionally been used for special purposes, it is far more desirable from the stand- point of simplicity and flexibility to measure direction, as well as range, from a single radar station. Measurement of target bearing was made possible by the development of radio techniques on wavelengths short enough to permit the use of highly directional antennas, so that a more or less sharp beam of radiation could be produced by an antenna of reasonable physical size.

When the pulses are sent out in such a beam, echoes will be received only from targets that lie in the direction the beam is pointing. If the antenna, and hence the radar beam, is swept or scanned around the horizon, the strongest echo will be received from each target when the beam is pointing directly toward the target, weaker echoes when the beam is pointed a little to one side or the other of the target, and no echo at all when it is pointing in other directions. Thus, the bearing of a target can be determined by noting the bearing of the radar antenna when that target gives the strongest echo signal. This can be done in a variety of ways, and more precise and convenient means for determining target bearing by means of radar have been developed (Chap. 6), but the method described here illustrates the basic principle.

It is convenient to arrange the radar display so that, instead of show- ing target range only, as in Fig. 1.3, it shows the range and angular disposition of all targets at all azimuths. The plan-position indicator, or PPI, is the most common and convenient display of this type. Figure 1.1 is a photograph of a PPI-scope. The direction of each echo signal from the center of the PPI shows its direction from the radar; its distance from the center is proportional to target range. Many other forms of indication are convenient for special purposes; the various types of indicator are cataloged in Chap. 6.

1.3. Components of a Radar System.—A radar set can be considered as separable, for the purposes of design and description, into several major components concerned with different functions. Figure 1.4 is a block diagram of a simple radar set broken up into the components ordinarily distinguished from one another.

In the set illustrated in Fig. 1“4, a cycle of operation is begun by the

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SEC.1.3] COMPONENTS OF A RADAR L9YSTEM 7 firing of the modulator. This sends a high-power, high-voltage pulse to the magnetron, which is the type of transmitting tube almost universally used in modern radar. For the brief duration of the modulator pulse, which may typically be 1 ~sec, the magnetron oscillates at the radio frequency for which it is designed, usually some thousands of megacycles per second. The r-f pulse thus produced travels down the r-f transmission line shown by double lines in Fig. 1.4, and passes through the two switches designated as TR and ATR. These are gas-discharge devices of a very special sort. The gas discharge is started by the high-power

Rotatingantenna

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J tRf echo pulses /’J Mixer

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Video l-f

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t Echo pulses I

J’

o

Angle data from scanner

Indicator

zwming pUIS.Sindicatingimtant of transmission (i.e. Zero range)

FIG.1.4.—Blockdiagramofa simpleradar.

r-f pulse from the transmitter, and maintained for the duration of that pulse; during this time the TR (for transmit-receive) switch connects the transmitter r-f line to the antenna, and disconnects the mixer and the rest of the radar receiver shown below the TR switch. The ATR (for anti-TR) switch, when fired, simply permits the r-f pulse from the transmitter to pass through it with negligible loss. Between pulses, when these gas-discharge switches are in an unfired state, the TR switch connects the rnher to the antenna, and the ATR disconnects the magnetron to prevent loss of any part of the feeble received signal.

After passing through these two switches, the transmitter pulse travels down the r-f line to the antenna, where it is radiated. The

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8 INTRODUCTION [SEC.1.4 antenna is designed in such a way that the beam shape it produces is suitable for the requirements the radar set must meet. It is mounted on a scanner which is arranged to sweep the beam through space in the manner desired; simple azimuth rotation is indicated in Fig. 1“4.

After the transmission of the pulse, the discharges in the TR and ATRstitches cease andthesystem isready to receive echoes. Echoes are picked up by the antenna and sent down the r-f line to the mixer.

The mixer is a nonlinear device which, in addition to receiving the signals from the antenna, is supplied c-w power from a local oscillator operating at a frequency only a few tens of megacycles per second away from the magnetron frequency. The difference frequency that results from mixing these two signals contains the same intelligence as did the original r-f echoes, but it is at a sufficiently low frequency (typically, 30 Me/see) to be amplilied by more or less conventional techniques in the intermediate- frequency amplifier shown. Output signals from the i-f amplifier are demodulated by a detector, and the resulting unipolar signals are further amplified by a video-frequency amplifier similar to those familiar in television technique.

The output signals of the video amplifier are passed to the indicator, which displays them, let us say for definiteness, in plan-position form.

In order to do this, it must receive a timing pulse from the modulator, to indicate the instant at which each of the uniform range sweeps out from the center of the PPI tube should begin. It must also receive from the scanner information on the direction in which the antenna is pointing, in order that the range sweep be executed in the proper direction from the center of the tube. Connections for accomplishing this are indicated in the Fig. 1.4.

In Chaps. 9 to 14, inclusive, the detailed design of each of the components shown in Fig. 1.4 is treated. In addition, consideration is given to the problem of supplying primary power in a form suitable for use with a radar set; this is especially difficult and important in the case of airborne radar.

1.4. The Performance of Radar.-In discussing the performance of radar, one usually refers to its range pwforrnunce-that is, the maximum distance at which some target of interest will return a sufficiently strong signal to be detected. The factors that determine range performance are numerous and they interact in a rather complicated way. Chapter 2 is devoted to a discussion of them, and Chap. 3 deals with the important matter of the properties of radar targets.

The usual inverse-square law which governs the intensity of radiation from a point source acts to determine the range dependence of the fraction of the total transmitted energy that falls on a target. So far as the echo is concerned, the target can also be thought of as a point source of radia-

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SEC.1.4] THE PERFORMANCE OF RADAR 9 tion, so that the inverse-square law must be applied again to determine the range dependence of the amount of echo energy reaching the receiver.

In consequence, the echo energy received from a target varies with the inverse fourth power of the range from the radar set to the target, other factors being constant.

To be detectable, a signal must have a certain minimum power; let us call the minimum detectable signal tlti~. Then the maximum range of a radar set on a target of a given type will be determined by Smi.,

according to the expression

S.n = g,

where K is a constant and Pt is the power in the transmitted pulse, to which the received signal power will clearly be proportional. Rearranging,

()

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R-= ~ . (2)

m.

Equation (2) displays the difficulty of increasing the range performance of a radar set by raising its pulse power. A 16-fold increase in power is required to double the range.

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3.2 cm A=locm, A

~ 1000 -—+- /

s .s 5s 100 s j

10

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0 1940 1941 1942 1943 1944 1945 Date

100

80 :E

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20 /

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0 1940 1941 1942 1943 1944 1945 Date

FIG.1.5.—Historicaldevelopmentof microwavemagnetrons.

However formidable this requirement appears, one of the most remarkable facts of the wartime years of development of radar is that practicable pulse powers in the microwave frequency range (about 1000 Me/see and above) have increased by a factor of hundreds in a relatively short time. This stupendous advance resulted from the invention and rapid improvement of the multicavity magnetron, which is described in Chap. 10. Figure 1.5 shows the history of magnetron development, with respect to pulse power and efficiency, at the three most important microwave bands exploited during the war. The curves are rather arbitrarily drawn, and only their general trend is significant. Not every upward

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10 INTRODUCTION [SEC.14 step in output power was due to an improvement in the magnetron itself.

The increase at 10-cm wavelength in the early part of 1941 was brought about by the development of modulators of higher power.

It is important to realize that the curves of Fig. 1.5 lie above one another in the order of increasing wavelength not because development was begun earlier at 10 cm than at 3 cm, and earlier at 3 cm than at 1 cm, but because magnetrons of the type used in radar are subject to inherent limitations on maximum power which are more severe the shorter the wavelength. The same is true of the r-f transmission lines used at microwave frequencies. The horizontal dashed lines shown in Fig. 15a show the maximum power that can be handled in the standard sizes of

‘‘ waveguide” used for r-f transmission at the three bands.

A similarly spectacular decrease in the minimum detectable signal, due to the improvement of microwave radar receivers, has marked the war years. In the wavelength bands above about 10 m, natural “static”

and man-made interference set a rather high noise level above which signals must be detected, so that there is little necessity for pursuing the best possible receiver performance. This is not true at microwave frequencies. Natural and man-made interference can be neglected at these frequeficies in comparison with the unavoidable inherent noise of the receiver. This has put a premium on the development of the most sensitive receivers possible; at the end of 1945 microwave receivers were within a factor of 10 of theoretically perfect performance. Improvement by this factor of 10 would increase the range of a radar set only by the factor 1.8; and further receiver improvement can today be won only by the most painstaking and difficult attention to details of design.

Why Microwave s?-The reader will have observed that when radar is discussed in what has gone before, microwave radar is assumed. This is true of the balance of this book as well. So far as the authors of this book are concerned, the word m.dar implies not only pulse radar, as has already been remarked, but microwave pulse radar. Though it is true that the efforts of the Radiation Laboratory were devoted exclusively to microwave pulse radar, this attitude is not entirely parochialism. The fact is that for nearly every purpose served by radar, microwave radar is preferable. There are a few applications in which longer-wave radar is equally good, and a very few where long waves are definitely preferable, but for the overwhelming majority of radar applications microwave radar is demonstrably far more desirable than radar operating at longer wavelengths.

The superiority of microwave radar arises largely because of the desirability of focusing radar energy into sharp beams, so that the direction as well as the range of targets can be determined. In conformity with the well-known laws of physical optics, by which the sharpness of

RADAR SYSTEM ENGINEERING