MICROWAVE MAGNETRONS

. ..’. . . .., ,., - ,/,’,’ , <:d

h’ +. .

MASSACHUSETTS INSTITUTE OF TECHNOLOGY

RADIATION LABORATORY SERIES

Board of Editors

LouIs N. RIDIiXOUR, Editor-in-Chief

GEORGE B. COLLIXS, Deputy Editor-in-Chief

BBITTO~ CHANCE, S. A. GOUDSMIT, R. G. HERB, HUBERT M. J.WIES, JULIAN K. KNIPP,

J.4MIis L. LAWSON, LIMJNB. LINFORD, C.lROL G. MONTGOMERY, C. NEWTON, ALBERT

M. STONE, LouIs A. TURNER, GEORGE E. V.\ LLI;Y, JR., HERBERT H. WHEATOS

1. RAILiR SYSTEM E~cl~]sl;R1~o—Ridenour

2. RADAR AIDS TO N.ivl&imoN-HalZ

3. RADAR 13EACONS-l?Obe?tS

4. LoRAx—Pierce, McKenzie, and Woodward

5. PULSE GEN):RATORS—GkJSOe and Lebacqz

6. MICROWAVE MAGNETRONS—COZknS

7. KLYSTRONS AND MICROWAVE TR1om-Han~itton, Kntpp, and Kuper

8. PRINCIPLES OF MICROWAVE CIRcul’r—Mon@omerv, Dic!ie, and PurceU

9. MICROWAVE TR.iNSMISSION CIRculTs—Ragan

10. WAVEGUIDE HANDROOK-}fa7’CUV~~Z

11. TECHXIQUE OF h~lCROWAVE MEASURENIENTS—MOntgO??LerY

12. MICROWAVE ANTENN.i THEORY AND I) EsIGN-i3i2ver

13. PROPAGATION OF SHORT R.iDIOWAvEs—Kerr

14. MICROWAVE DUPLEXERS—i%LUll~n and Montgomery

15. CRYSTAL RECTIFIERS—TOrreY and Whatmer

16. MICROWAVE MIxERs—Pound

17. COMPONENTS HANDBOOK—~kZLLkbU?Vt

18.19.

20.

21.22.23,24.25.26.27.28,

VACUUM TUBE AJIPLIFIERS—ValleY and Wallman

W.\VEFORXS—Chance, Hughes, MacNichol, Sayre, and Wtlliams

ELECTRONIC TIMIS ME.\ SURENfENTS—GhanCe, Hulsazer, MacNichol,and Williams

ELECTRONIC iNSTRUMENTS—GreenWOOd, Hotdam, and MacRae

CATHODE RAY TUBE DISPLAYS—SOller, Starr, and Valley

MICROWAVE RECEIVERS—Van Voorhis

THRESHOLD SIQNALS—LaWSOn and Uhlenbeck

THEORY OF sERvo>lEcHAN1sM-JanLes, Nichols, and Phillips

RADAR SCANNERS AND EADOMES—Cad~, Karetitz, and Turner

COMPUTING MECHANISMS AND LINKAQES—SVObOdU

lNDEx—Henney

MICROWAVEMAGNETRONS

Edited by

GEORGE B. COLLINSDEPARTMENT OF PHYSICS

UNIVERSITY OF ROCHESTER

OFFICE OF SCIENTIFIC RESEARCH AND DEVELOPMENT

NATIONAL DEFENSE RESEARCH COMMITTEE

FIRST EDITIonr

NEW YORK. TORONTO LONDON

MCGRA TV-HILL BOOK CO JIPANY, INC.

1948

MICROWAVE MAGNETRONS

COPI-RIGHT,, ]94S, BY THE

31CGRAW-HILL BOOK C;OMPAYY, lYC.

PRINTED IX-THE U>’ITED STATES OF .UUERIC.*

.4[1 Tighl.s resewed. This book, or

parl.s thereof, mav not be ?f>j3TOd11Cd

in an?) .form u:ilhollt per771ission of

the p~[blzshers,

m“wEd

THE MAPLE PREsS COMPAKY, YORK, PA

MICROW’A VE MAGNETRONS

EDITORIAL STAFF

GEORGE B. COLLINS

A. FINEMANJOYCE KINNEY

CONTRIBUTING AUTHORS

J. G. BUCKA. M. CLOOSTONG. B. COLLINSJ. R. FELDMEIERM. A. HERLINN. M. KROLLS. MILLMANF. F. RI-EKEA. G. SMITH

w. ~. SMITE

L. R, WALKER

Foreword

T HE tremendous research and de~ ~lopment effort thfit went into thedevelopment of radar and related techniques during World lVar II

resulted not only in hlmdreds of radar sets for military (and some forpossible peacetime) use but also in a great body of information and newtechniques in the electronics and high-frequency fields. Because thisbasic material may be of great value to science and engineering, it seemedmost important to publish it as soon as security permitted.

The Radiation Laboratory of MIT, which operated under the super-vision of the Nationll Defense Research Committee, undertook the great

task of preparing these volumes. The work described herein, however, isthe collective result of work done at many laboratories, Army, Na\’y,university, and industrial, both in this country and in England, Canada,and other Dominions.

The Radiation Laboratory, once its proposals were approved an{!finances provided by the Office of Scientific Research and Development,chose Louis N. Ridenour as Editor-in-Chief to lead and direct the entireproject. An editorial staff was then selected of those best qualified forthis type of task. Finally the authors for the various volumes or chaptewor sections were chosen from among those experts who \vere intimatelyfamiliar with the various fields, and who were able and ]villing to writ,’the summaries of them. This entire staff agreed to remain at work alMIT far six mcmths or more after the work of the Radiation Laboratorywas complete. These volumes stand as a monument to ibis group.

These volumes serve as a memorial to the unnamed hundreds andthousands of other scientists, engineers, and others who actually carriedon the research, development, and engineering work the results of whichare herein described. There were so many involved in this \vorkand theyworked so closely together even though often in widely separated labora-tories that it is impossible to name or even to know those who contributedto a particular idea or development. Only certain ones who wrote repor::or articles have even been mentioned. But to all those who contributed.in any way to this great cooperative development enterprise, both in this

%count ry and in I?nglaml, these volumes are dedicated.@

L. A. DUBRIDGE.- Gi

$

v\\\

Preface

THEpulsed 10-cm magnetron, perfected by the British in 1940, const i-tuted the starting point for the development of microwave radar.

From that time until the end of the war the magnetron proved to be oneof the most important components in radar systems. As a consequenceof this, the armed services, both in this country and in England, insti-gated extensive programs of research and development to produce newtypes and improve the characteristics of existing ones. The programsoon became a major one for the electronic industry. At the RadiationLaboratory alone, over forty highly trained physicists and engineers spentmore than four years studying magnetron performance and producingnew designs. Comparable effort was expended by the many otherindustrial and research laboratories. The result was over twenty dis-tinct types of magnetrons, producing powers in the tens to thousands ofkilowatts at frequencies that were largely unexplored before 1940. Whatis more important, this program led to a better understanding of theprinciples of magnetron operation and to an increased appreciation ofthe importance of the field of electronics at high frequencies.

During the war very little attention could be given to evaluating,correlating, and recording these new developments, and what reportswere \vritten are disconnected and incomplete. Actually, much of theinformation existed only in the minds of the investigators and in theirpersonal notebooks. ‘l’he purpose of this book is to present in a usableform this large amount of theoretical and practical knowledge.

Conditions surrounding the preparation of the volume producedspecial problems. The time available was short, considering the amountand complexity of the material, and a division of labor among manyauthors was necessary. ‘l’his permitted the selection of authors bestqualified to present different subjects but resulted in a not too consistentstyle and level of presentation. Furthermore, it was appreciated thatalthough microwave magnetrons were developed for use in radar systems,their importance to science and engineering was much broader; thus thematerial for the book was evaluutmf largely in terms of its possible futureusefulness, and the uncertainty of this resulted in a tendency to include

ix

x PREFACE

too much rather than too little. More serious aretheerrors that maynot have been eliminated because of insufficient time for adequate review.

The book contains a large fraction of what was known, as of January1946, about the theory, design, and operation of magnetrons in thefrequency range 1000 to 25,000 Me/see and the many modifications thatextend the usefulness of these tubes. There is in this book, because ofits radar background, a strong emphasis on magnetrons intended forpulsed operation, but the treatment is extended to c-w applicationswhenever possible.

The scope is dictated by the primary premise that all informationnecessary to” make a magnetron” be included. As a result, the characterof the chapters ranges from a detailed theory of the various aspects ofmagnetron operation to the details of construction of production magne-trons. An introductory chapter reviews the early work on magnetrons,including the first 10-cm tube of the British, and presents the basicprinciples of magnetron operation in order to orient the reader unfamiliarwith the subject.

Except for this introduction, the material is arranged so that theoryprecedes practical considerations. A final chapter gives operating dataand important dimensions for a variety of magnetrons.

Although the authors of this volume were nearly all members of thehI IT Radiation Laboratory or Columbia Radiation Laboratory, a greatdeal of the material included originated in the industrial concerns of thiscountry and England. References to contributions by other laboratoriesis given whenever possible, but the free exchange of information existingduring the war makes the origins of many of the ideas uncertain. Inparticular, the contributions of the Boll Telephone Laboratories and theRaytheon Manufacturing Company have been extensive and in manycases undistinguishable from those of the MIT and Columbia groups.The important contributions of these and the many other institutions areacknowledged.

The early work of the British deserves special recognition. All toofew references to it are found in this volume, because soon after theoriginal design was divulged to laboratories in this country, the develop-ment here proceeded along rather independent lines. The British magne-tron, however, was the key to the production of high-power microwaves.A discussion of this tube and its important features is found in Chap. 1,based on material kindly furnished by Professor J. T. Randall andDr. H. A. H. Boot who, more than any others, were responsible for itsinvention.

Acknowledgments are due to the many who reviewed chapters of thebook. In particular, mention should be made of Dr. Lewi Tonks of theGeneral Electric Company, Drs. W. B. Hebenstriet and H. D. Hagstrum

PREFACE xi

of the Bell Telephone Laboratories, Drs. A. Nordsieck and A. V. Hollen-berg of Columbia University, Dr. Lloyd P. Smith of Cornell University,and .Miss Helen Wieman for her assistance in preparing the manuscriptfor publication.

In conclusion, the editor wishes to emphasize that a book of thismagnitude could not have been \vritten without the wholeheartedcooperation of all the authors, many of whom worked on the manuscriptlong after leaving the Radiation Laboratory.

GEORGE 13. COIjLINS.

(?AMBRII)GE, hfASS.,

July, 1946.

Contents

]K)Rk;~OR~ BY ],. A. ]) U13RIIWE. vii

1’ltl;FA(;l,;........,. . . ..ix

CHAIJ. 1. lN~lWDU(~’~IOIi 1

1.1,

1.2.

1.3.

14.

1.5.

1,6.

1,7.

1.8.

1+).

1.10.

1.11.

Fkly Types of hfagnctrons.The British (’avity Magnetro]lDescription of a Nlicrrrwavc Nlagllt,trollThe lkwonant SystcrnThe Cathorl r......The Space (;hargr.D-c Vrrltagc hfagnctic-firld ItdationshipComponent }Iodcs.Efhcicncy and Frrqut,ncy Stability.Performarrcc (;htirts and Rieke Diagrau)sPulsed hfagnetrons

PART I. RESONANT SYSTEMS

CHAP. 2. THE UNSTRAPPED RESONANT SYSTEM

2.1. The hfagnetron Cavity as a Circuit Problem2.2. Equivalent Network for the Side Resonators2.3. Equivalent Network for the Interaction Space.2.4. Spectrum Predicted by tbe Equivalent Network.2.5. Admittance of Side Resonators by Field Theory.2.6. Admittance of the Interaction Space by Field Theory2.7. The Spectrum Predicted by Field Theory,2.8. End-space Effects . . . . . . . . . . . . .2.9. The Interaction Field . . . . . . . . . . . . . . . . . . .2.10. Applications and Limitations . . .2.11. The Computation of Admittances

CHAP. 3. THE RISING-SUN SYSTEM.

3.1. The Spectrum . . . . . . . .3.2. The Interaction Field.3.3. The Effect of the Mode Spectrum and Field Characteristics on

~-mode Operation . . . . . . . . .3.4. The Effects of Various Parameters on the Mode Spectrum and the

Interaction Field of a Ricing-sun Magnetron !,,.

Xlll

49

4952525456636669747677

83

8392

98

101

xiv CON TEN TS

3,5. Closed-end Rising-sun S@cms . . . . . . . . . 110

36. The Unloaded Qand #C/~. . . . . . . . . . . . .113

CHAP. 4. THE STRAPPED SYSTEhf . . . . . . . . . . 118

4.1. Introduction . . . . . . . . . . . . . . . . . . . . . .. 1184.2. Analysis of Strapped Systems . . . . . . . . . . 12143. Rings ofiXetworks . . . . . . . . . . . . . . . . . . . . . 123

SYMM~TRICAL SYSTEMS . . . . . . . . . . . . . . . . . . .. 131

4.4. Fixed-frequency Systems . 13145. Effects of Various Parameters OILt!lv 3!w1c, Spcctrulll 135

AsYL1llRrRICAL SYSTTSMS . 140

46. Pattern Distortion and hIodc-s[wctru],il’f[(xts (’auscd by I,oadirlg 1414.7. f3ffccts of Strap Breaks. 1474.8. Effects Caused by Various Types of Tuning. 157

CHAP. 5. OUTPUT CIIiCUITS, . . . . . . . . . . . .. 167

51. Introduction . . . . . . . . . . . . . . . . . . . . . ,. 16752. The 4-terminal Transducer 1715.3. The Q-circle alld the Riclw Diagram 1785.4. General (~onsidcrations Concerning the Output (’ircuit l’mblcm 1875.5. Coaxial-output Circuits 1915.6. Waveguide-output Circuits . 194

PART II. ANTAI,YSIS OF 01’ERATION

CHAP. 6. THE INTERACTION’ ON THE ELE(’TROX”S AN-D THE ELEC-TROMAGNETIC FIELD. . 207

6.1, Introduction . . . . . . . . . . . . . . . . . ,. 20762, The Assumptions Underlying the Analysis . 2096.3. The Field Equations. . . . . . . . . . . ,., ..21764. The Equations of Lfotion. . . 22265. Conditions Under Which Relativistic IMects Lfay Pm Eliminatc,d 2286.6. The Nonrelativistic Equations. “. 23167, SymmetricalStates. .2436.8. The Bunemann Small-amplitude ThcOry 25364). Analysis by the Lfethod of SeH-consistent Fields. 2656.10. Qualitative Discussion of the Interaction 274611. Departures from the Rotating-wave Hypothesis, 282

CHAP. 7. TI-IE SPACl; CIIARGE .4S A CIR(’tJIT EI,K31ENT 288

7.1.72.7.3.7.4.7.5.7.6.77.

I1ltro{l~lc,tion .,...,, . . . . .. 288The Electi-on Strealn as a [’ircuit Elemrnt . 2!)1Analysis of t,hc Resonant System , 297Interactions Between Space Charge and Resonator, 305The Description of hlagnetron Performance. 316The hfismatched Transmission Line as a Resonant Load 320Experimental Data on the Space-charge Properties. 329

CONTENTS xv

CHAP. 8. TRAIW31~~T JlE1L4V10R . . . . . . 339

81. Steady-state Properties of the Modes. . . . . . . . 33!)

82. Steady-state Properties of the Pulser, . . . . 343

83. Typcsof hlode Changes. . . 345

84. Survey of the Process of hfode S.election . . . . 34885. TheAfodeSkip . . . . . . . . . . . . . . . . . . . 350841. ThehIode Shift . . . . . . . . . . . . . . . . . . . . 3518,7. Instability of the Power Supply: “ Mode Jumps” . 35588. Outline of a Theory of Starting 35789 Observations and Discussion of Starting 367810, Ohscr\ations on R-f Buildup . . . 372811 Effect of Design and Operation on Sturting . . . 37(;8.12. ]ntcractions Between Jlodm . , . . . . 380

c[l\P.!l.NoIsi3. . . . . . . . . . . . . . . . . . . . . . . . ...388

91. Introduction. ,.. , . . . . . . . . . . . . . . . ...3889.2. Pre-oscillation Noise . . . . . . . . . , . . . . . 38!)93. Signal-to-noise Ratin. . . . . . . . , . . . . . . 3949.40rigins OfNoisc . . . . . . . . . . . . . . . . . . . . ..3!)5

PART III. DESIGN

c}!.,p, 10. PRINCIPLES OF Dl?SICX , . . . . 401

10,1. The Primary Design Parameters. . . . . 40]10,2, The 31ethod of Nlagnetrorr Design, 40310,3. Conditions Imposed on the Itesonant System 406104. Conditions Imposed on the Cathode 411105. Conditions Imposed on the hlagnetic (’ircllit . 414106. TbeScalingLaws. ... . . . . . . . . . . . . . . .. 41410.7. Reduced Operating Data on Various Types of \l~gm.trous 41{)108, Determination of the secondary Design Parameters 43510.9.comparison of tbe Reduced Performance ( ‘harts. 441

1010. The Universal Performance (’hart . 44810,11, The General Design Formulas. . 4541012, Numerical Example. . 4.58

~H.\P. 11. THE RESOX.4NT SYSTEX1. . . . . 460

11.1. Factors Influencing (%oict= of Rwwmant Systpm . . . . 4(XI

,STRAPPEDRESONANT .SYSTEMS . . . . . 461

11.2. Wavelength and Chmocteristic Admitt:mcr. , . . . . 46111.3. Unloaded Q........ . . . . . . . . . . . . . ...46611.4. hlode Separation . . . . . . . . . . . . . . . . . . ...468

RISINC+UN RESONANT SYSTEMS . . . . . . . 470

11.5. Limitations on Secondary Design Parameters . 47211.6. Desirable 3[ode Spectrum 474117. Comparison Between @sn-reeanator and Closed-end Systems. 47711.8. Ratio of Resonator Depths 47811.9. Wavelength Calculations for the ~-mode 47!4

xvi CONTENTS

OUTPUT, . ., .,.,,..,. . . . . . . . . . . . . . . . . . 481

11.10. General Properties of Coaxial and Waveguide Gutputs. 481

11.11 .~axial output s..,.,, . . . . . . . . . . . . . . . . 482

11.12. Ckaxial-to-waveguide Transitions 485

11.13 .Waveguide Outputs . . . . . . . . . . . . . . . . . ...486

11.14. Waveguide Transformers 491

11.15. Examples of Waveguide Output. . . . 497

11.16. End-space Geometry. . . . . 498

CHAP. 12. THE CATHODE . . . . . . . . . . . . . . . . . . . ...503

EMISSION PHENOMENA or MAGNETRON CATHonEs . 503

12.1. Characteristics of Cathodes under Pulsed Conditions. 503

12.2. Alkaline-earth Oxide Cathodes—Test Methods 505

12.3. Alkaline-earth Oxide Cathodes—I,ife Tests and Sparking Phe-nomena . . . . . . . . . . ,,, ..,..508

12.4. Thorium Oxide Cathodes. . . . 51512.5. Secondary Electron-emission Properties of Magnetron Cathodes 517

HEAT BAHNCEIN THE CATHODE. . . . . . . . . . ,. 519

12.6. Thermal Behavior of a Pulsed Cathode. 52012.7. Measurements of Back-bombardment Power 52512.8. Thermal Considerations in Cathode Design 528

ESTABLISHMENT OF AN AXIAL BOUNnARY TO THE SP.ACE CHARGE 537

12.9. Cathode End Shields., ,537

CHAP. 13. THE MAGNETIC CIRCUIT 54o

13.1. Design of Permanent Magnets. 54013.2. Magnet Charging . . . . . . . . . . . . . . . . . . . 54813.3. Magnetic Stabilization . . . MO13.4. Field Uniformity . . . . . . . . . . . . . . . . . . . .,55213.5. Testing and Measurements . 553

PART IV. TUNING AND STABII,IZATION

CHAP. 14. MECHANICAL TUNING. . 561

14.1. General Considerations. 561

INDUCTNE AND CAPACITNE TUNING . 564

14.2. Symmetric Inductive Tuning: Sprocket Tuning 56514.3. Symmetric Capacitive Tuning: The Cookie Cutter. . 57o14.4. . Other Symmetric Inductive and Capacitive Methods of Tuning 57214.5. Unsymmetric Inductive Tuning 575

COUPLEn-CIRCUIT TUNING. . , .’ 576

14.6. General Theory...,.. ., ..,,....,.....576

14.7. Double-output Tuning . . 576

14.8. Symmetric Double-output Tuning. . 582

14.9. Cavity Tuning . . . . . . . . . . . . . . . . . . . ...583

14.10. Single-stub Tuning. . . 589

fY3h’TE.VT,~ xvii

CHAP. 15. IH,JIXTRONIC TUNING . . 592

ELECTRON-BEAM TUNING . . . . . 592

15.1. General Considerations. 59215.2. Fundamental Equations of Beam Tuning. 594153. The Principles of Electron-beam Tuning in a Magnetic Field 59915,4. The Engineering Equations of IOectron-beam Tuning 60415.5. Scaling . . . . . . . . . ...61015.6. Internal vs. External Cavity Tuning. . . 611

NIAGNETHON DIODE TUNING. 615

15.7. Fundamental Principles 61515.8. Small-signal Theory : 61615.9. Experimental Data on I,arge-sigrral Conditions .,, 619

15.10 . Other Methods . . . . . . . . . . . . . . . . . . . ...621

CHAP. 16. STAB~LIZATION OF FREQIJENCI-. 622

16.1. Introduction . . . . . . . . . . . . . . . . . . . . ...62216.2. The Ideal Stabilizer . . . .. 62416.3. Coupling hlethods . . . . . . . . . . . . . . . . . . ...62616.4. hleans of Damping the Extraneous hfodes 63316.5. The Design of Stabilizing Circuits 639

PART V. PRACTICE

(% AP.17, CONSTRUCTION . . . .649

17,1. Fabrication of Arrode Blocks 64917.2. Brazing and Soldering 66217.3. Selected Brazirrg Problems 67017.4. Chemical Processes 67417.5. Mrtal-t&glaaa 8eals. .67617.6. Cathode and Heater Construction 68517.7. Tube Evacuation and Processing 69317.8. Examination of Metals. 694

CHAP. 18. hIE.4SUREillENTS. . 698

N[EASUREMENTS OF THE RESONANTSYTSEM 698

18.1. Test Equipment Components 69818.2. Cavity-wavelength Measurements 70218.3. Measurement of Standing }Yaves 705

18-4. Field-pattern Measurements 710

18.5. hlessurementof Q. . . 713

18.6. The Stabilization Factor 723

18.7. hiagnetrcm-mode Identification . 72618.8. Cathode-lead Load..... . . . . . . . . . . . . ...72818.9. Tube-model Techniques. .729

OPERATING hfEASUREMENTR . . . . . . . . . . . . . .. 730

18.10. hfeawring Techniques 73218.11 . Operating Technique.. .735

...x Jill (’O.YTI?.VT,?

rH.\P. 19. TYPIC.kL LIAGNETROXS . . 739

19.1. The LCW Lband Cw hIagnetron. 74o19.2. The C1116B S-band C-w Magnetron. -. 74419.3. 2J3&2J39 Low-voltage S-band llagnetrons 74719.4, TYPe 2J22-2J34 lo-cm Pulsed ~Iagnetrons . 751

195. 4J70-4J77 High-power S-band Tunable I[ag]lrtrons 75619.6. The HP1OV High-power S-band hIagnetron. 76019.7. The B\150 Very Low Power .X-band llagnetron. 76419.8. 2J41 Low-po\ver Stabilized X-band lIngnetrou 76619.9, The 2J42 Imw-voltage X-band Jlagnetron 77019.1O. The 725A ilIagnetron 7741{).11. The 2J51 Xlagnetron, . 7781!).12. 4J50 (4J52, 4578) High-po\vcr 3-cm XIagnctron 78019.13. The AX9 Rising-sun JIagnctron. 7841914, The 3J31 and 3J21 Rising-sun lIagnctrons 78619.15. 22-cavity Rising-sun IIagnetron . 7!)01916. The Closed-end 38-ca\,ity Rising-sun Xlagnrtron. 791]{).17. The XCR High-po\vcr 2.Gcm (’-;v X1:ignetron, 795

TNr)Ex. . . . . . . . . . . . . . . . . . . . . . . . . . . . . ...797