LOU IS N. RI D E NOU R,
Edi m-in-Chiej
 
RAD I ATION LAB ORATORY S E RI E S
B oa r d of E dit ors
h um N. RIDENOUB, Editor-in-Chief
GEOBGEB. COLLINS, Deputy Editor-in-Chief
BRITTON CHANCE, S. A. GOUDSMIT, R. G. HESS, HUBEBT M. JAMES, JULIAN K. KNIPP,
JAMES L. LAWSON, LEON B. LINFOSD, C.iROL G. MONTOOHEBY, C. NEWTON, ALBERT
M. ST NE, LOUIS A. TUBNEB, GEORGEE, VALLEY, JII., HEItBEBT H. WHEATON
1. RADAIi SYSTEM ENQ1NEEBIN*~2denOUr
2. RADAB AIOS TCI NAVlt3ATION—HU21
3. RADAB BEACONB-ROZIefk
4. Lo iN-Pierce, McKenzie, and Woodward
5. P U L S E G E N E B ATO S S -ola S O e and Lelmcqz
6. MICaOWAVE MAGNETRONS-COzlinS
7. KLYSTRONS ANO MICROWAVE TRIODES—HUmi~tOn, Knipp, and Kuper
8. PRINCIPLES OF MICBOWAVE CIRculTs—MontgotnerV, llicke, and PurceU
9. MICBOWAVE TRANSMISSION CmculTs-Ragan
12. MICKOWAVS ANTENNA THEORY AND DES1~N—Si2Ver
13. PROPAGATION OF SHOBT R.\DIO WAvEs-Kerr
14. MICROWAVE lluFLExEss-8mul11n and Montgomery
15. CBYSTAL RECTIFIERS—TOrre~ and Whitmer
16. MICBOWAVE MIxERs—Pound
Ii’. COMPONENTS HANDDooK—Blackburn
19. WAVEFORhfS-ChanCe, Hughes, Mach’ichol, Savre, and Williams
20. ELECTRONIC TIME ME.UNJREMENTS—C7hUnCe,Htdsizer, MocNichol,
and Williams
22. CATHODE RAY TUBE DIsFLAYs—soUer, Starr, and Valle~
23. MICROWAVERECEIVERS—V(M2 Voorhis
25. THEORY   sERvolIEcH.\NIsMs-James, Nichols, and Phillips
26. RADAS SCANNEBS ANO RADOMES-Cadu, Karelitz, and Turner
27. COMPUTING MECHANISbiS AND LINKAGEs—Svoboda
28. lNDEX—Henne~
 dited hy
.4SSIST.ANT PROFESSOR OF ELECTRICAL Eh~~~NEE~lN~
THE OIINS HOPKIINS IJA-IIERSITY
N .\ T1ON AL DEFENSE IiES13ARCH COMMITTEE
FIRST ~DITIO\
J~ ~J ’  O ZK  l LO.VDON
i l f rG1/ .i T fr -f I I L L BOOI { G’031PAATY I .WC.
194s
 4
THE MAPLE PRESS COMPANY, YORK, PA.
 
 \
J E AN V. LE B AC QZ
H OWARD D . D OOLI TTLE
B ARB ARA D WI G HT
CONTRIBUTING AUTHORS
J . R. D I LLI NG E R
L. G . KE RS TA
P . C . E WARD S
H . H . K OS K I
O. T. F U ND I NG SLAND
J . V. LE RAC QZ
K . J . G E RME S H AU S E N
R. S . S TANTON
H . J . WH ITE
Forewrd
T
HE tremendous research an(l dcwelopmcnt effort ttlat \v(,r)t, i r]f (~ 1,111.
development of raclar ancl relatecl techniques durin g N’fJ r l~ l \ \ ”:L r I I
r esult ed n ot only in hundreds of ra da r set s for milit a ry (a ml s(J [n(: f’(J r
possible pea cet ime) use but a lso in a gr ea t body of inf~ )rmut i(m urlfl n{w
t ech niq ues in t h e elect r onics a nd h igh-freq uen cy ficlr ls. lJ C CWM t 1,is
ba sic ma ter ia l ma y be of gr ea t va lue t o scien ce a nd engin eer in g, it s{:l.rn~ ,l
most import a nt t o publish it a s soon a s secur it y permit t ed.
The Ra dia t ion La bora t ory of MI T, w h ich opera ted under t }w su lx.r-
vision of t he Na t iona l D efen se Resea rch C ommit tee, undm-t of)k t }w gr~ , :lt ,
t a sk of pr epa r in g t hese volum es.
Th e w or k descr ibed }w r rin , t L(J t r ,v(r ,is
t h e collect ive result of w or k don e a t ma ny la bora t or ies, ,I rmy, X uvy,
universit y , a nd indust r ia l, bot h in t his coun t ry a nd in E ngla nd, ( ‘a nw lu,
a n d ot h er D om in ion s.
The Ra dia t ion La bora t ory , on ce it s proposa ls w er e a ppr oved a nd
fina nces pr ovided by t he Office of S cient ific Resea rch a nd D evelopm en t ,
ch ose Louis N. Riden our a s E dit or-in-C hief t o lea d a nd direct t h e ent ire
pr oject . An edit or ia l st a ff w a s t h en select ed of t h ose best qua lified for
t his t ype of t a sk. Fina lly t h e a ut hors for t h e va rious volumes or ch a pt ers
or sect ion s w er e ch osen from a mong t h ose expert s w ho ~ ~ ere int ima tely
fa milia r w it h t h e va r ious fields, a nd w h o w er e a ble a nd w illing t o \vritc
t h e summa ries of t h em. This en t ire st a ff a greed t o rema in a t ~ vor k a t
MI T for six mont hs or more a ft er t h e w or k of t h e Ra dia t ion a bora t ory
w a s com plet e. Th ese volumes st a nd a s a monument t o t his gr oup.
These volumes serve a s a memoria l t o t h e unn a med hundreds a m]
t housa nds of ot her cien t ist s, en gin eers, a nd ot her s w ho a ct ua lly ca rr ied
on t he resea rch , developmen t , a nd en gin eer in g w or k t he result s of w hich
w or ked so closely t o et her even t bough oft en in w ide] y sepa ra ted la bora -
t or ies t ha t it is impossible t o na me or even t o kn ow t hose ~ v h o cont ribut ed
t o a pa rt icula r idea or developmen t . On ly cer t a i on es w ho \ vrot e repor t s
or a rt icles h a ve even been men t ion ed. B ut t o a ll t h ose w ho cont r ibut ed
in a ny w a y t o t his grea t cooper a t ive developmen t en t er pr ise, bot h in t his
coun t ry a nd in E ngla nd, t hese volumes a re dedica ted.
L . A. DUBRIDGE.
 
EN the Radiation Laboratory was organized in the fall of 1940 in
order to provide the armed services with microwave radar, one of
the important technical problems facing this group was that of devising
equipment capable of delivering high-power pulses to the newly dev loped
cavity-magnetron oscillator.
electrical pulses were available at this time. However, the special
characteristics of these magnetrons and the requir ments imposed by t e
operation of a microwave-radar system (high pulse power, short pulse
duration, and high recurrence frequency) made it evident that new
techniques had to be developed.
During the existence of the Radiation Laboratory the group assigned
to the problem of pulse generation grew from a nucleus of about five peo-
ple to an organization of more than ten times this number. The coordi-
nated efforts of this group extended the development of pulse generators
considerably beyond the original requirement of 100-kw pulses with a
duration of 1 psec and a recurrence frequency of 1000 pps. The develop-
ment extended to both higher and lower powers, longer and shorter
pulses, and lower and higher recurrence frequencies. Besides the
improvement of existing techniques, it was necessary to devise entirely
new methods and to design new components to provide satisfactory pulse
generators for radar applications. The use of a lumped-constant trans-
mission line (line-simulating network) to generate pulses of specific pulse
duration and shape was car ied to a high state of development. As a
result of work both on transformers that could be used for short pulses
and high pukw powers and on new switching devices, highly efficient and
flexible pulse generators using line-simulating networks were available
at the end of the war. oncurrent with the work at t e Radiation
Laboratory, a large amount of work was done at similar laboratories in
Great Britain, Canada, and Australia, and at many commercial labora-
tories in this country and abroad.
The purpose of this volume is to present the developments in the
techniques of pulse generation that have resulted from thk work. These
techniques are by no means limited to radar applications: they may be
used with loads of almost any conceivable type, and should therefore be
applicable to many problems in physics and engineering. The discussion
of pulse-generator design and operation is divided into three principal
parts. Part I is concerned with hard-tube pulsers, which are Class C
ix
x
PREFACE
amphfiers specifically desi ued for the production of pulses of short
duration and high power; Part II presents the characteristics of the
line-type pulser, which utilizes the line-simulating networks; Part III
considers the d esign a n d ch a r a ct er ist iccs of pu lse t r a nsfor mer s.
Through-
out t his volum e bot h t he t heoret ica l a nd t h e pra ct ica l a spect s of pulse-
genera t or design a re given in or der t o a void rest r ict ing t he a va ila ble
inform a tion t o ra da r a pplica t ions.
Alt hough t he m a jor pa r t of t his volume is w rit t en by a few m em bers
of t h e Ra dia t ion L a bor a t ory st a ff, ma ny ot her individua ls a t t he Ra di-
a t ion La bora t ory a nd elsew h er e ha ve cont r ibut ed t heir idea s in t h e
prepa ra t ion of t hk ma t er ia l, a nd w e h ereby a ckn ow ledge t heir con-
t ribut ions. P a r t icula r m ent ion m ust be m a d of t he work done by Miss
Anna Wa lt er in connect ion w it h m a ny of t he m a t hem a t ica l a na lyses.
H er pa inst a king w or k in checkin g t he ma t hema t ica l der iva t ions a nd
m a king t he long a nd t edious ca lcul a t ions necessa ry for ma ny of t he curves
a nd num erica l exa mples is gra t efully cknow ledged. We a r e gla d t o
a ckn ow ledge a lso t he w or k of Miss F . New ell D ut t on, w ho processed t he
num erous pulse phot ogr a phs t ha t a ppea r t hroughout t h e VOIum e.
We a re a lso indebt ed t o t he ma ny people w h o ha ve cont r ibut ed t heir
t im e fr eely in rea ding va rious cha pt er s a nd sect ions of t he ma nuscript ,
a nd w h o ha ve m a de va lua ble suggest ions for t he im provem ent of t h e
discussion. We w ish t o a cknow ledge t he help r eceived in t his w a y
from Mr. J . P . H a gen a nd his a ssocia t es a t t he Na va l Resea rch La bora -
t ory ; D r . J . E . G orha m a nd his a ssocia t es a t t he Arm y S igna l C or ps
La bora t ory ; D r . F . S . G ouch er , Mr. E . P . P a yne, Mr. A. G . G a nz, Mr.
A. D . H a sley, Mr. E . F . O’Neill, a nd Mr. W. C . Tinus of t h e B ell Tele-
phon e L a bora t or ies; Mr. E . G . F . Ar not t , Mr. R . L ee, Mr. C . C . H orst -
ma n, a nd D r. S . S iegel a nd his a ssocia t es a t t he West inghouse E lect r ic
E . Whit ford of t h e Ra dia tion L a bora tor y a nd t he U niversit y of Wiscon-
sin; a nd D r. P . D . C r out of t he Ma ssa chuset t s I nst it ut e of Technology.
Th e prepa ra t ion of t he m a nuscr ipt a nd t he illust ra t ions for t his
volum e w ould ha ve r eq uir ed a much longer t im e if w e ha d not ha d
Ra dia t ion L a bora t or ies. We w ish t o express our a pprecia t ion of t he
effor t s of Mr. C . New ton,’ hea d of t his depa rt m ent , for his help in get t ng
t he w or k done pr om pt ly a nd a ccura tely.
C A M S F U D G E ,MASS.,
Juns, 1946.
THE AUTHORS.
 ontents
FORE WORD B Y L. A. D U B B I D G E . . . . . . . . . . . . . . . . . vii
P RE FAC E . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
CE AP .l. I NTROD U C TI O . . . . 1
1.1. P a a met ers F unda ment a l t o t he D e ign of P ulse G ene a t or e. . 1
1.2. The B a sic C ircuit of a pulse G ener a t or . 5
1.3. H a rd-t ube P ulsere . . . . . . . . . . . . . 6
1.4. Line-t ype P ullers . . . . ..8
1.5. A C ompa r ison of H a rd-t ube a nd Line-t ype P uleers. 13
P ART I. TH E H ARD -TU B E P U LS E R
CHAP. 2. THE OUTPUT CIRCUIT OF A HARD-TUBE PULSER. 21
2.1. The Basic Output Circuit.. 21
TH E D I S C H AR G I NGOF THE STORAGE CONDENSER. . . 25
2.2. The Output Circuit with a Resistance Load. 26
2.3. The Output Circuit with a Biased-diode Load. 32
TEE CHARGING OF THE STORAGE CONDENSER 51
2.4. The Output Circuit with a High Resistance as the Isolating
Element . . . . . . . . . . . . . . . . . . . . . ...5
2.5. The Output Circuit with an Inductance or an Induct ve Resistor
asthe Isolating Element.. 61
POWER TRANSFER TO THE LOAD . . . . 69
2.6. I rnpeda nce-ma t ching a nd P ulse-t ra nsformer C oupling t o t he Loa d 70
2.7. The E ffect of S t ra y C a pa cit a nce on t he P ula er P ow er Out put 76
243. Out put P ow er Regula t ion . . 77
29. E ffect s of P ulse-t ra nsfor mer C oupling t o t he Loa d 78
CH AP . 3. VAC U U M TU E S AS S WI TC H E S . 90
3.1. Req uir ed Cha ra ct er ist ics 9(I
3.2. The C ha ra ct er ist ic C urves for Tr iodes a nd Tet rodes a nd t heir
I m port a nce t o t he Funct ion of a P ulser S w it ch Tube. 98
3.3. The E ffect of S w it ch-t ube a nd Loa d C ha ra ct er is ics on t he
P uleer Regula t ion . . . . . . . . . . . . . . . . ...108
xi
xii
CONTENTS
C H AP . 4. D RI VE R C IRC U ITS . . . . . . . . . . . . . . . . . . . . . 119
4.1. Tbe B oot st ra p D r iver , . . . . . . . . . . . . . . . ...120
4.2. Th e B lockin g Oscilla t or or Regen er a t ive D r iver . 124
4.3. Th e Mult ivibra t or a n d pulse-for min g-n et w or k D r iver s . 132
CH AP . 5. P ARTI C U LAR AP P LIC ATI ONS . 140
5.1. Th e Model 3 P ulee*A Ligh w eigh t Medium-pow er P ulser f r
Air born e Ra da r S yst ems . . . . . . . . . . . . . . ...140
5.2. Th e Model 9 P u ser -A 1-Mw H a rd-t ube P ul er . 152
5.3. A H igh -pow er S hort -pulse H a r d-t ube P ulser . 160
5.4. Th e Applica tion of pulse-sha pin g Net w or ks t o t he H a rd-t ube
P ukw r . . . . . . . . . . . . . . . . . . . . . . ...165
P ART II . TH E LINE -TYP E P U LS E R
CHAP. 6. THE PULSEFORMING NETWORK. 175
6.1. The Formation and Shaping of Pulses . . 175
6.2. Networks Derived from a Transmission Line 179
6.3. Guillemin’s Theory and the Voltage-fed Network 189
6.4. Current-fed Networks. . . . . .207
6.6. Test Procedures . . . . . . . . . . . . . . . . . . . 221
C H AP . 7. TH E D I S C H ARG I NG C I RC U I T OF TH E LI NE -TYP E P U LS E R 225
7.1. G ener a l P roper t ies of t h e D ischa rging C ircuit 225
7.2. P ulser C ha ra ct er ist ics. . . 233
7.3. P ulser Regula t ion a n d E fficien cy . 244
7.4. Th e D isch a r gin g C ircuit a n d P ulse S h a pe. . 255
7.5. C omput ed a n d Act ua l P ulse S ha pes . 261
CH AP . 8. S WITC H E S FOR LINE TYP E P U L E RS . . 273
TH E ROTARY S P AE K G AP ..,. . . . . . . . . . . . .275
8.1. E lect r ica l C on sidera t ions in t h e D esign of Rot a ry S pa rk G a ps. 276
8.2. C onsidera t ions of Mecha n ica l D esign . 283
8.3. Rot a r y-ga p per for ma n ce . . . . 289
ENCLOSED FIX D SPARK GAPS.. . . . . . . . . . . . . .. 294
8,4. General operating Characteristics of series Gaps. 296
8.5. Trigger Generators...,.. . . . . . . . . . . . . . ..3o4
8.7. General Considerations for Gap Design. . 316
8.8. The Cylindrical-electrode Aluminum-cathode Gap 318
8.9. The Iron-spong Mercury-cathode Gap. . 327
8.10. The Three-electrode Fixed Spark Gap 332
THE HYDBOGEN THYRATRON. ... . . . . . . . . . . . . 335
8.12. The Anode Circuit . . . . . . . . . . . . .. 344
8.13. The Grid Circuit . . . . . . . . . . . . . . . . . . . ...349
 
mu
C H AP . 9. TH E C H ARG I NG C TRC U I T OF TH E LI E -TY E P U LS E R 355
I ND U C TANC EC H ARG I NGFROM A D -c P OWE R SU P P LY. 356
9.1. en er a l Ana lysis of D-c C ha rging . 356
9.2. P ra ct ica l D -c C ha rging Rea ct ors. . . . . . . 364
9.3. The D esign of D -c C ha rging Rea ct ors . . . 372
INDUCTANCE CHARGING FROM AN A-c SOURCE. . . . . 380
9,4. G en er a l Ana lys s of A-c C ha rging . . . . 380
9.5. A-c Resona nt C ha rgi g. . . . . . . 386
9,6. A-c Nonresona nt C ha r ging 393
9.7. P ra ct ica l A-c C ha rging Tra nsformers. . . 400
98. The D esign of H igh-rea ct a nce Tra nsform ers. . . 407
9 . Miscella neous C ha r ging C ircuit s. . . . . . 414
CHAP. 10. PERFORMANCE OF LINE-TYPE PULSJ3RS . . . 417
10,1, E ffect s of C a nges in Loa d I m peda n ce . . . . 417
102. S hor t C ircuit s in t he Loa d. . . . 423
10.3. Open C ircuit s a nd P r t ect ive Mea sures. . . . 431
PULSER PERFORMANCE WITH A MAGNETRON LOAD. . . . . . . . . . 435
10.4. Nor ma l Opera t ion of t he Ma gnet ron . . . . 435
10.5. Ma gnet ron h’lode-cha nging . . . 438
103. Ma gnet ron S pa rking. . .441
CHAP. 11. P ARTI C U LAR AP P LI C ATIONS . . . . . . . 448
111.
11.2.
11.3.
11,4.
11.5.
116.
11.7.
11.8.
A H igh-pow er Rot a r y-ga p R.dser . . . . . . . 448
A H igh-pow er Airborn e P ulser . . . 454
Mult iple-net w ork P rdsers. . . . . . 463
The Anger C ircuit .,.. ... . . . . . . . . . . . ...468
The N onlinea r-induct a nce C ircuit . . 471
S pecia l-purpose ht put C ircuit s . . 476
Mult iple-pulse Line-t ype P ulsers. 485
Mult iple-sw it ch C ircuit for Volt a ge Mult iplica t ion . 494
P ART III . P U LS E TRANS FORME RS
CHAP 12. E LE ME NTARY TH E ORY OF P U LS E TRANS FORME R 499
12,1. G en er a l Tr nsformer Theor y 499
122. Va lues of E lement s in t he E q uiva lent C ircui 510
CHAP. 13. PULSE-TRANSFORMER DESIGN. 532
13.1. General Pulse-transformer Design Considerations 532
13,2. Design Methods . . . . . . . . . . . . . . . 536
CHAP. 14. EF ECT OF PULSETRANSFORME PARAMETERS ON
CIRCUIT BEHAVIOR . . . . . . . . . . . . . . . . ...563
14.1.
The E ffect of P ulse-t ra nsformer P a ra met ers on P ulse S ha pes on
 
C ON TE .V TS
14.2. The E ffect of P ulse-t ra nsformer P a ra met ers on t he B eha vior of
Rcgrncra t ivc P ulse (genera t ors. 575
143. The E ffect of l’ulsc-t ra nsformer P a mmct crs on Freq uency
Rmponsc . . . . . . . . . . . . . . . . . . . ...591
CHAP 5 J IATl~ RI AIS AXD TI I E I R U S E S I X D E S I C N 5 )9
(“ORl~llATfi:RIA1....... 599
151. D -c I ’ropw t irs a n d Test Result s. 599
152. P ulse Xla gnet iza t in n 613
15.3. I {;ncrgy I mss a nd lt q uiw drmt ( ‘ircuit s 626
15.4, .\ dr iit iona l Aspect s of I ’uls J la gnct iza t ion 633
155. Trchniq urw for \ I ca sur ing (‘ore P mforrna ncc 639
COIL ll.iTERI~L . . . . . .
157. J Virc . . . . . . . . . . .. 655
App~ ND rx A. }lE .WG RI XG TE C H IQU E S 661
OSCILLOSCOrlC \lETHOLrS. . . . . . . .. 662
A3. I’ractical Considerations in Making Pulse hIcasurements 687
A,4. Voltage and Currcut llcasurcments in t he C ha rging C ircuit of a
Line-t ype P ulsa r .,,...... . .,.....,,.,690
METEFLING TECHNIQUES . . . . . . . . . . . 692
A7. Auxilia ry hlca sur ing Techniq ues. 706
APPENDIX B. PULSI? DURATION AND AMPI,lTUDE 710
B .1. 13q uiva lcnt Rect a ngula r P ulse by C onserva t ion of C ha rge a nd
E nergy. . . . . . . . 711
B 2. F;q uiva lw rt Rect a ngula r P ulse by hlinimurn D epa rt ure Area s 716
B 3. .4 C ompa rison of t he lfet hods. 720
I .lS TOF S YII I I O1,S . . . . . . . .. 723
I ND E X . . . . . . . . . . . . . . . . . . . . . . . . . . . . .. 729
 
INTRODUCTION
B Y G . N. G L AS OE
Microw a ve ra da r ha s req uired t h e developmen t of pulse gen era tor s
t ha t a re ca pa ble of producing a succession of pulses of ver y shor t t ime dura -
t ions. Th e pulse gen era t ors of a ra da r syst em fa ll in t o t w principa l
ca tegor ies, na mely, t hose t ha t a re a ssocia t ed w it h t h e t ra nsmit t er a nd
t h ose t h a t a re used in t h e indica tor a nd ra nging circuit s. Th e principa l
dist inguishing fea t ure of pulse gen er a t ors of t hese t w o t ypes is t he out p t
pow er level. Th e ra da r t ra nsmit ter req uires t he gen er a t ion of high -pow er
a nd h igh-volt a ge pulses w h erea s t h e in dica t or a nd ra ngin g circuit s
req uire pulses of negligible pow er a nd rela t ively low volt a ge.
The pur-
pose of t his book is t o r ecor d informa tion t h a t per t a ins t o t h e ba sic pr in-
ciples un der lying t h e design of pow er pulse gen er a tors. Alt h ough most
of t hese principles h ave been developed prima rily in t he field of microw a ve
ra da r, t h ey a re eq ua lly a da pt a ble t o a ver y la rge number of a pplica tions
n ot a ssocia t ed w it h ra da r . Th e discussion is genera l, a nd r efer en ce t o
specific microw ave-ra da r a pplica tions is ma de only w hen t h ey ser ve a s
exa mples of a t t a ina ble result s.
S pecific design informa tion is given for
some of t he pra ct ica ble circuit s t ha t ha ve been built a nd h a ve pr oved t o
b e s a t i sf a ct or y .
The most common ly used sour ce of t h e high-freq uency en ergy t ha t is
n ecessa ry for microw ave ra da r ha s been t h e ma gnet ron oscilla tor . The
problem of pow er-pulse-gen era tor design ha s, t h er efore, been gr ea t ly
in fluen ced by t h e cha ra ct erist ics of t hese ma gnet ron oscilla t ors. B y
vir t ue of t h is a pplica t ion ma ny of t he ba sic pr inciples of pulse-genera t or
design a r e bet t er un der st ood.
The pow er pulse gen era tor s used in t h e t ra nsmit t ers of ra da r syst ems
h a ve been va riously refer red t o a s “modula tors,” ‘‘ pulsers,” a nd (‘key-
ers.” S ince t h e funct ion of t h ese gen era tor s is t o a pply a pulse of volt a ge
t o a n oscilla tor a nd t her eby produce pulses of h igh -freq uen cy en er gy t o
be ra dia ted by t h e a nt enna , t h e t er m ‘ pulser
“ is a descr ipt ive a bbrevia -
t ion for pulse gen era t or . Through out t his book, t h erefore, t h e t er m
“ pu ls er ”
w ill be used in pr efer en ce t o t h e t erms ‘( modula t or ” a nd
“keyer.”
1.1. P a ra met ers Funda ment a l t o t h e D esign of P ulse G en era tors.—
Th ere a r e cer t a in pa ra met ers of a pulser t ha t a re c mmon t o a ll t ypes
m
2
ZNTRODUCTIOX
[SEC.1.1
a nd t ha t a ffect t h e design. Th e most import a nt of t h ese pa ra m et ers
a re pulse dura t ion, pulse pow er , a vera ge pow er , pulse r ecur ren ce fre-
q uency, dut y ra t io, a nd im peda nce level. B efore proceed n g t o t h e
det a iled discussion of pulser design, t h er efore, it is w ell t o in t roduce t h e
pa ra met ers by defining some t erms a nd indica ting t h e ra nges w hich h a ve
been com mon in t he microw a ve-ra da r field.
In it s broa dest a spect s, t he t erm “pulse dura tion” is t h e t ime during
w hich a volt a ge or cur rent ma int a ins a va lue differen t from zero or som e
ot h er init ia l a nd fina l va lue. Th e t erm “ pulse sha pe” is used t r efer
t o t h e form obt a ined w h en t h e pulse a mplit ude is plot t ed a s a funct ion of
t ime. When referr in g t o such a plot , it is con ven ien t t o discuss t h e det a ils
of a pa rt icula r pulse sha pe in t erm s of t h e “lea din g edge,” t he “t op,”
a nd t he “t ra iling edge” of t he pulse.
I f a pulse of volt a ge or curren t is
t ruly rect a ngula r in sha pe, t ha t is, ha s a n eg igible t ime of r ise a nd fa ll
a nd is of const a nt a mplit ude for t he int erven in g t ime in t erva l, t h e pulse
dura t ion is simply t h e t ime ela psed bet w een h e devia tion from a nd t h e
ret urn t o t h e init ia l va lue. Th e t erm “negligible t im e” is, of course,
rela tive a nd n o st r ict bounda r ies ca n be a tt a ched.
F or most pra ct ica l
purposes, h ow ever , if t h e r ise a nd fa ll t imes for a pulse a re a bout a t ent h
or less of t h e pulse dura t ion, t h e pulse is con sidered subst a nt ia lly r ec-
t a ngula r. A curren t pulse of t his t ype is req uired for a m a gnet ron oscil-
la tor by vir t ue of t h e depen den ce of t h e out put freq uen cy on t h e curren t ,
w hich i ca lled t h e “pushing fa ct or . ”
F or pulses w hich a re definit ely
n ot rect a ngula r, t h e effect ive or eq uiva lent pulse dura tion is eit h er t h e
t ime mea sured a t some fra ct ion of t h e a ximum pulse a mplit ude t ha t is
significa nt t o t h e pa rt icula r a pplica tion, or t h e t ime correspon din g t o a
rect a ngula r eq uiva lent of t h e pulse in q uest ion.
The int erpret a t ion of
pulse dura t ion is discussed in Appendix B , a nd w hen pa rt icula r ca ses
com e up in t h e t ext t hey a re con sidered in m ore det a il.
The pulsers t ha t h a ve been designed for microw a ve-ra da r a pplica -
t ion s h a ve pulse dura t ions coverin g t h e ra n ge of 0.03 t o 5 ~ sec.
Th e
design of a pulser for short pulse dura t ions w it h subst a nt ia lly rect a ngula r
pulse sha pe req uires t he use of high -freq uency circuit t echniq ues sin ce
freq uencies a s h gh a s 60 t o 100 hlc/sec cont r ibut e t o t he pulse sha pe a nd
t he effect s of st ra y ca pa cit a nces a nd in duct a nces become serious.
In t h e m icrow a ve-ra da r field t he volt a ge req uired a cross t h e ma gnet -
ron ra n ges from a s 10]v a s 1 kv t o a s big-h a s 60 kv. I f a volt a ge pulse is
a pplied t o some t y p of ciissipa tive loa d, a ma gnet ron for exa mple, t h ere
w ill be a correspon din g pulse of curren t w h ich depends on t h e n a ture of
t his loa d. Th e pulse curren t t hrough t h e ma gnet ron r nges from a few
a mperes t o severa l hundred a mperes.
Th e com bined considera t ions of
sh ort pulse dura tion a nd rect a ngula rit y t erefore req uire t ha t ca reful
 
3
under condit ions of high ra t es of cha nge of volt a ge a nd cur rent . Thr
ra t e of cha nge of volt a ge ma y be a s high a s severa l hundred kilovolt s
per m icrosecond, a nd t h e curr ent ma y build up a t t he r a te of hundreds t o
t housa n ds of a m per es per m icr osecon d.
The pr oduct of t he pulse volt a ge a nd t he pulse urr en t is t he pulse
power.
When t he volt a ge a nd curr ent pulses a re rect a ngula r , t h e cor -
respo ding pulse pow er is una mbiguous. When t he pulses a re ir regula rly
sha ped, h w ever , t he mea nin of t he t er m “pulse pow er ” is not so clea r
beca use somew ha t a rbit ra ry m et hods a re oft en used t o a vera ge t he pr od-
uct of volt a ge a nd cur ren t during t he pulse.
The pea k pow er of a pulse
is t he ma ximum va lue of t he product of t he volt a ge a nd cur rent . Thus,
for rect a ngula r pulses t he pea k pow er a nd t he pulse pow er a re t he sa me,
but for irregula rly sha ped pulses t he pea k pow er is gr ea t er t ha n t he pulse
power.
In t his connect ion ’ t her e a re t w o genera l t ypes of loa d t ha t a r e dis-
cussed most fr eq uent ly , na mely, t he linea r loa d, such a s a pur e resist a nt e,
a nd t he nonlinea r loa d, such a s t he m a gnet ron.
The m a gnet r on loa d
ca n be a pproxima t ely repr esen t ed a s a bia sed diode w it h a dyna mic
resist ance t ha t is low a nd a st a t ic resist ance t ha t is a bo t t en t imes higher .
S t a tic resist a nce is t he ra tio of t he volt a ge a cr oss t he loa d t o t he cur rent ,
t hrough t he loa d, w herea s t he dyna mic resist a nce is t he ra t io of a sma ll
cha nge in volt a ge t o t he correspo ding cha nge in curr ent .
When t he
dyna mic resist a nce of t he loa d is sma ll, t he ma gnit ude of t he pulse cur -
r ent va ries grea t ly w it h only sma ll va ria t ions of t he pulse volt a ge, a nd for
loa ds such a s a ma gnet ron, for exa mple, t he beha vior of t h e pulser w it h a
linea r loa d is n ot necessa rily a good cr it er ion.
S ince t he pulse-pow er out put of pulsers for m icrow a ve-r a da r a pplica -
t ion ha s ra nged fr om a s low a s 100 w a t t s t o a s high a s 20 Mw , t he a ver a ge
pow er out put a s w ell is import a nt t o t he design. The a ve a ge pow er
cor respondin g t o a pa r t icula r pulse pow er depends on t he ra t io of t he
a ggr ega te pulse dura tion in a given int erva l t o t h e t ot a l t ime, a nd t his in
t ur n depends on t he pulse r ecur r en ce freq uency, P RF, w hich is t he num-
be of pulses per second (pps). I f t he pulse dura t ion is 7 a nd t h e t ime
bet w een t he beginning of on e pulse a nd t he beginning of t he next pulse
is
1’
A simila r eq ua t ion ca n be w rit t en in t er ms of t he cur ren t if t h e pu se
volt a ge is essent ia lly const ant during t he t ime cor responding t o t he cur-
r en t pulse, t hus
 
[SEC.1.1
S ince t he a vera ge current a nd t he P RF a re rela t ively ea sy t o mea sure,
t his rela t ion ma y be used t o define a pulse current if t he t op of t he pulse
is irregula r but t he rise a nd fa ll t imes a re negligibly sma ll. I t ma y a lso
be use t o define a n equiva lent pulse dura t ion for a pulse sha pe t ha t is
t ra pezo da l a nd perha ps rounded a t t he t op, but l\ here some significa nce
ca n be a t t ached t o a pulse-current mea surement .
The ra t io T/T,—or t he product 7(1’RF)—is commonly a lled t he
pulser “ dut y,
“ ‘f dut y cycle, ” or prefera bly “ dut y ra tio, ” a nd is expressed
a s a fra ct ion or a percent a ge. Thus l-psec pulses repea t ed a t a ra t e of
1000 pps correspond t o a dut y ra t io of 0.001 or 0.1 per cent . P ulsers
ha ve been const ruct ed ~ vit h a dut y ra tio a s high a s 0.1, but for most ra da r
a pplica tions a va lue of 0.001 or lolver is most common.
As ~ vit h a ny
pow er device, t he over-a ll efficiency of a pulser is a n import a nt considera -
t ion in it s design. This is pa rt icula rly t rue ]Vhe t he a vera ge po~ ver out -
put is high, t ha t is, a combina t ion of high pulse po er a n high dut y
ra tio. This point is st ressed in t he discussion a nd is freq uent ly a decid-
ing fa ct or in choosing one t ype of pulser in preference t o a not her .
The pulse recurrence freq uency a ffect s t he design of a pulser in w ays
ot her t ha n from t he st a ndpoint of t he po~ r er considera t ions.
Th e pu ls er
circ it ma y be considered t o ha ve a q uiescent st a t e t ha t is dist urbed
d ring t he pulse int erva l a nd t o \ rhich it must ret urn before t he init ia t ion
of t he ne t succeeding pulse.
I f t he P RF is very high, t he problem of
ret urning t he circuit t o t his q uiescent st a t e becomes of import a nce
S uch t hings a s t ime const a nt s a nd deioniza t ion t imes ma y impose a
limit on how sma ll t he int erpulse int erva l ca n be \ vit hout unduly com-
plica t ing t he design.
This limit becom es especia lly import a nt \ rh never
it is necessa ry t o produce a series of closely spa ced pulses t o form a code
such a s is used in ra da r bea cons.
The choice of t he int erna l impeda nce of t he pulse genera tor depends
on t he loa d impeda nce, t he pulse-pol’:er level, a nd pra c ica l considera -
t ions of circuit element s. Impeda nce-ma tching bet lreen genera tor a nd
loa d is of prime import a nce in some ca ses, especia lly w it h rega rd t o t he
proper ut iliza t ion of t he a va ila ble energy a nd t he product ion of a pa rt icu-
la r pulse sha pe. Impeda nce-ma tching is not a lw a ys convenient w it h t he
loa d connect ed direct ly t o t he puls r out put ; hoirever , ma t ching ca n
rea dily be a t t a ined by t he use of a pulse t ra nsformer.
B y t his mea ns it is
possible t o obt a in impeda nce t ra nsforma tions bet w een pulser a nd loa d
a s high a s 150/1, t ha t is, a t ra nsformer w it h a t urns ra t io of a bout 12/1.
The ma gnet rons ~ ~ -hichha ~ ,e been used in micro~ va ~ ,e ra da r ha ve st a t ic
impeda nces ra nging from a bout 400 ohms t o a hout 2000 ohms; in genera l,
t he higher t he pow er of t he ma gnet ron, t he low er it s input impeda nce.
Th e im peda n ce-t ra n sfor ma t ion cha r a ct erist ic of t he pulse t ra n sfor mer
 
5
Thus t h e pow er ma y be t ra nsmit t ed f om t he pulser t o t he loa d t hr ough a
low -im peda nce coa xia l ca ble, pr ovided t ha t pulse t ra nsfor m ers a re used
t o ma t ch impeda nces. F or m ost efficient pow er t ra nsfer such im peda nce-
ma t ching is necessa ry bet w een pulser a nd ca ble a nd bet w een ca ble a nd
loa d. In t his w a y it ha s been possible t o t ra nsmit high-pow er pulses of
sh ort dur a t ion over a s much a s 200 ft of ca ble w it hout a ser ious loss in
t he over -a ll eficiency or a det er iora t ion of t h e pulse sha pe.
The pulse t ra nsform er ha s a not her funct ion t ha t is impor t a nt t o pulser
design, na mely, it provides a m ea ns for rever sing t he pola rit y of a pulse.
This fea t ur e of t he pulse t r a n sform er t oget h er w it h t he im peda nce-
t ra nsform a t ion pr oper t y considera bly ext ends t he r a nge of usefulness for
pulsers of a ny t ype.
1.2. The B a sic C ircuit of a P ulse G ener a tor .—Th e pulse gen er a tor s
discussed in t his book depen d on t he st or a ge of elect r ica l en er gy eit h er
in a n elect r st a t ic field or in a ma gnet ic field, a nd t h e subseq uent dis-
ch a r ge of a fra ct ion or a ll of t his st or ed en er gy int o t h e loa d. Th e t w o
ba sic ca t egor ies int o w hich t he la rgest num ber of pulse designs logica lly
fa ll a r e (1) t hose in w hich only a sma ll fra ct ion of t h e st or ed elect r ica l
en er gy is discha rged int o t h e loa d during a pulse, a nd (2) t h ose in w hich
a ll of t h e st or ed en er gy is disch a rged during ea ch puls . Th ese t wo ba sic
ca t egor ies of pulsers a re genera lly r efer r ed t o a s (1) “ha rd-t ube pulsers”
a nd (2) “line-t ype pulsers. ”
To a ccomplish t his discha rge, it is necessa ry t o pr ovide a suit a ble
sw it ch t ha t ca n be closed for a lengt h of t im e cor r esponding t o t h e pulse
dura t ion a nd m a int a ined open during t he t im e
1
t
req uir ed t o bui d up t h e st or ed en er gy a ga in be-
 __J
Energy-
for e t he n ext succeeding pulse. In it s simplest
s torage
Swi tch
for m , t h er efor e, t h e discha rging circuit of a
pulser ca n be r epr esen ted schem at ica lly a s show n
in Fig. 1.1. The cha ra ct er ist ics req uir ed for t h e
Load
sw it ch w ill be differ ent depen ding on w het her or
not a ll t he st or ed en er gy is discha rged int o t he FI G . 1.1.—B rw icdischm g-
loa d during a single pulse. S om e pulse-sha ping
in g cir cu it of a p uk er .
w ill be necessa ry in t h e discha rging cir cuit w h en a ll t h e n er gy is t o be
dissipated.
S ince t he cha rging of t he ener gy-st or a ge com ponent of t he pulser
t a kes pla ce in t he r ela t ively long int erpulse int erva l, t h e discussion of
pulsers ma y logica lly be divided int o t he con sidera t ion of t he discha rging
circuit on t he on e ha nd, a nd t he cha r ging circuit on t he ot her . P ow er
supplies for ,t hese pulsers a r e, in genera l, of convent iona l design a nd
t h er efor e usua lly n eed not be discussed, but w h er ever t his design
ha s bea r ing on t h e over-a ll pulser beha vior , specia l ment ion is ma de
of t he fa ct .
 
6
INTRODUCTION
[SEC.1.3
1.3. H a rd-t ube P ulsers.-I n gen era l, t h e en er gy -st ora ge device for
t h eee pulsers is simply a con den er t ha t is ch a rged t o some volt a ge V,
t hus m a king a va ila ble a n a mount of elect r ica l en erg + C V2. The t erm
“h a rd-t ube” r efers t o t h e n a ture of t h e sw it ch, w hich is most comm on ly
a high-va cuum t ube cont a ining a con t rol gr id. Th e closin g a nd openin g
of t his sw it ch is t herefor e a ccomplished by a pplyin g pr operly con t rolled
volt a ges t o t h e gr id. S ince on ly a sma ll fra ct ion of t h e en er gy st ored in
t h e con den ser is disch a rged during t h e pulse, t h e volt a ge a cross t h e
sw it ch immedia t el a ft er t h e pulse a nd durin g t h e ch a rgin g in t erva l is
nea r ly t h e sa me a s it is a t t h e begin ning of t h e pulse.
I t is t her efore
n ecessa ry t h a t t h e gr id of t h e va cuum -t ube sw it ch ha ve com plet e con t rol
of t h e con duct ion t h rough t h e t ube.
This req uired ch a ra ct er ist ic of t he
sw it ch t ube rules out t h e possibilit y of using kn ow n ga seous-discha rge
devices for t his t y pe of pulser.
I t is gen era lly desired t ha t t hese pulsers pr oduce a succession of pulses,
a nd t h er efore some provision must be m a de t o replenish t h e ch a r ge on
t h st ora ge conden ser . This is a ccomplished by mea ns of a pow er supply
w hich is con n ect ed t o t he con den ser durin g t he int erpulse in t erva l.
Th e
supply
C h a r gin g D isch a r gin g
p k “r c”” -4
T[
condenser
Load
for a ha rd-tubepulser.
combina tion of t h e discha rging
a nd ch a rgin g circuit s of t he pulser
m a y be r epr esen ted sch em a tica lly
a s show n in F ig. 1.2. In o der t o
a void sh ort -circuit in g t h e pow er
supply during t h e pulse int erva l,
som e form of isola t ing elem en t
must be provided in ser ies w it h
t h e pow er supply . This elem en t
ma y be a high resist a n ce or a n
in duct a nce, t he pa rt icula r ch oice
depen din g on t h e req uirem en t s of
over-a ll pulser design . The pri-
ma ry con sidera tion is t o keep t h e
~ ow er-sumdv cur ren t a s sma ll a s
possible d ur in g t h e pulse in t er va l.
H ow ever , t h ~ ~ m -ped a nce of t his isola t -
ing elemen t should n ot be so high t ha t t h e volt a ge on t h e con den ser a t t h e
en d of t he in t erpulse in t erva l differs a pprecia bly from t h e pow er-supply
v olt a g e.
B eca use of t h e high pulse-pow er out put , pulsers for m icrow a ve ra da r
req uire sw it ch t ubes t h a t a r e ca pa ble of pa ssing high curren t s for t h e
sh ort t ime correspon din g t o t h e pulse dura t ion w it h a rela t ively sma ll
differ en ce in pot en t ia l a cross t h e t ube. Oxide-ca th ode a nd t h oria ted-
t un gst en -fila m ent t ubes ca n be ma de t o pa ss curren t s of ma ny a mperes
 
7
w it h a rea sona ble opera tin g life expect a ncy . Th e ca th ode efficiency ,
t ha t is, a mperes of pla te cur ren t per w a t t of hea t in g pow er , is c nsider-
a bly less for t h e t h oria ted-t ungst en fila ment t ha n for t h e oxide ca th ode.
F or sw it ch t ubes w it h oxide ca t h odes it ha s been com mo t o obt a n
a bout 0.3 t o 0.5 a m p/w a t t of hea t ing pow er , a lt hough a s m uch a s 1
a mp/w a t t ha s been obt a ined, w herea s for t hor ia ted-t un gst en fila ment s
t his a mount is genera lly less t ha n 0.1 a mp/w a tt . Th e t ungst en-fila ment
t ube, h ow ever , is less subject t o spa rking a t high v lt a ges a nd current s
a nd, w it h in Ra dia t ion L a bora t ory experien ce, t h ese t ubes ha ve n ot
exh ibit ed ca t hode fa t igue, t ha t is, a fa lling-off of ca t hode em ission during
lon g pulses. This ca thode fa tigue is somet im es a limit a tion on t h e long-
est pulse for w hich a n oxide-ca t hode sw it ch t ube should be used.
I n or der t o obt a in a high pla t e cur ren t in t h ese sw it ch t ubes, t h ere
must be a fa ir ly high posit ive volt a ge on t h e con t r ol gr id a nd t h erefor e
considera ble gr id curren t . In t h e ca se of a t et r ode, t h ere is a high screen -
gr id curren t a s w ell The dut y ra t io perm it t ed in a given pulser is oft en
limit ed by t h e a mount of a vera ge pow er w h ich t h e pa rt icula r t ube ca n
dissipate.
Th e out put circuit of a h a rd-t ube pulser does n ot usua lly cont a in a ny
prima ry pulse-sha pin g compon en t s, a lt hough it s design , in combin a t ion
w it h t h e loa d, ha s a ma rked effect on t h e ult ima t e sha pe of t h e pulse.
In a pulser of t his t ype, t h e pulse is form ed in t h e driver circuit , t h e out -
put of w h ich is a pplied t o t h e con t rol gr id of t h e sw it ch t ube. F rom t h e
st a ndpoin t of over-a ll pulser efficien cy , it is desira ble t ha t t h e sw i ch
t ube be n onconduct in g during t h e in t erpulse in t erva l. Th e con t rol gr id
must t h erefor e be a t a volt a ge sufficient ly n ega tive t o keep t h e t ube cut
off during t his t ime, a n conseq uent ly t h e out put volt a ge from t h e driver
must be sufficien t t o over com e t his gr id bia s a nd ca rr y t h e gr id posit ive.
F or m ost designs of ha rd-t ube pulsers, t h is req uiremen t mea ns t ha t t h e
driver out put pow er must be a few per cen t of t h e a ct ua l pulser out put
power.
The resist a n ce of a va ila ble va cuum t ubes used a s sw it ches in ha rd-
t ube pulsers ra n ges from a bout 100 t o 600 ohms. I f t h e pulser is con -
sidered a s a gen er a t or w it h a n int erna l resist a nce eq ua l t o t ha t of t h e
sw it ch t ube, t he high e t discha rge efficiency is obt a ined w hen t he effect ive
loa d resist a nce is high. Ma t ch ing t h e loa d resist a n ce t o t h e in t ern a l
resist a nce of t he pulser result s in a n efficien cy of 50 per cen t in t he out put
circuit a nd t h e w it ch t ube must dissipa t e a s much pow er a s t h e loa d.
B eca u se of t hese con sider a tion s, t he h a rd-t ube pulser is gen er a lly design ed
w it h a pow er-supply volt a ge slight ly gr ea t er t ha n t h e req uired pulse
volt a ge. This design pra ct ice ha s n ot been follow ed w h en t h e out put
volt a ge req uired is h igher t ha n t h e pow er-supply volt a ge t ha t is ea sily
 
a nd ot her specia l considera t ions. A
pulse t ra nsformer ma y t hen be used bet w een t he pulser a nd t he loa d t o
obt a in t he desired pulse volt a ge a t t he loa d.
1.4. Line-t ype P ulsers.—P ulse genera t ors in t his ca t egory a r e r efer red
t o a s ‘‘ line-t ype” pulsers beca use t he energy-st ora ge device is essent ia lly
a lumped-const a nt t ra n mission line.
S ince t his component of t he line-
t ype pulser serves not only a s t he source of elect r ica l en ergy during t he
pulse but a lso a s t he pulse-sha ping element , it ha s become commonly
knolvn a s a “ pulse-forming net vork,”
P FX. Ther e a re essent ia lly t w o
cla sses, of pulse-forming net lvor ks, na mely , t hose in w -hich t he en er gy for
t he pul e is st ored in a n elect rost a t ic field in t he a mount + C VZ, a nd t hose
in n-hich t his ener gy is in a ma gnet ic field in t he a mount + 512. The first
cla ss is referr ed t o a s “ volt a e-fed net works” a nd t he second a s “current -
fed n et w orks. ”
The volt a ge-fed n et w ork ha s been used ext ensively in
t he microiva ve-r a da r a pplica tions in pr efer ence t o t he current -fed net -
\ vor k beca use of t h e la ck of sa tisfa ct ory s vit ch t ubes for t he la tt er t ype.
The pulse-forming n et vork in a line-t ype pulser consist s of induc-
t a nces a nd condensers ~ rbich ma y be put t oget her in a ny one of a number
of possible configura tion . The configura tion ch sen for t he pa rt icula r
pur pose t ha nd depends on t he ea se w it h w hich t he n et w ork ca n be
fa br ica ted, a s \ vell a s on t h e spec fic pulser cha ra ct er ist ic desired. The
I ’a lues of t he induct a nce a nd ca pa cit a nce element s in such a net w ork ca n
be ca lcula t ed t o give a n a rbit ra ry pulse sha pe w hen t he configura t ion,
pulse dura tion, impeda nce, a nd loa d cha ra ct er ist ics a re specified. The
t heoret ica l ba sis for t hese ca lcula t ions a nd t he det a iled discussion of t he
o
role of t he va rious n et w ork pa ra met ers a re given
in P a r t I I of t his book.
Th e discha rging circuit of a line-t ype pulser
P FN
using a volt a ge-fed n et w ork ma y be r epresent ed
Switch
schema t ica lly a s sh w n in Fig. 1“3. I f ener gy
ha s been st or ed in t he n t w or k by cha rging t he
Load
ca pa cit a nce element s, closing t h e sw it ch w ill
a llow t he discha rge of t his ener gy int o t h e loa d.
When t he loa d impeda nce is equa l t o t he cha ra c-
F I G .
1.:l.—lli,rt l~ rg i]lg
t er i t ic impeda nce of t he net work, a ssuming t he
cucuit for a volt a ge-fed
sw it ch t o ha ve negligible r sist a nce, a ll of t he
I let \ Y,,l.
en ergy st or ed in t he net w ork is t r a n sferr ed t o
t he loa d, lea ving t h e condensers in t he n et w ork complet ely discha rged.
‘l’he t ime req uired for t his ener gy t ra nsfer det erm ines t he pulse dura tion
a nd depen ds on t he va lues of t he ca pa cit a nces a nd induct a nce of t he ne -
\ rork. I f t h e loa d impeda nce is not equa l t o t he net w ork impeda nce, some
en ergy w ill be left on t he r w t nw rk a t t he end cf t he t ime corresponding t o
 
9
t ions in t he circuit beha vior a nd is t o be a voided if possible by ca reful design
a nd const r uct ion of t he net w or k t o insure a n impeda nce ma t ch w it h t he
loa d. The volt a ge a ppea ring a cross a loa d t ha t ma t ches t h e im peda nce
of a nondissipa tive volt a ge-fed net w or k is equa l t o one ha lf of t he volt ag(
t o w hich t he n t w or k is cha rged just before
closin g t h e sw it ch .
Th e cor respon din g cir cuit for a cur ren t-fed
net w ork ma y be r epresent ed a s show n in Fig.
1.4. In t his ca se t he sw it ch a ct s t o close t he
net work-cha rging circuit a nd a llow s a curr ent
t o build up in t h e induct a nce of t he n et w ork.
When t his current is in t errupt ed by opening
t he sw it ch, a high volt a ge, w hose ma gnit ude
depends on t he loa d impeda nce a nd t he curr ent
in t he induct a nce, a ppea rs a cross t he loa d.
Impeda nce-ma tching bet w een t he loa d a nd a
net w ork of t he curr ent -fed t ype result s in a
t
Charging
discha rg ingcir cu it f or a CU r-
rent-fednetwork.
division of curr ent such t ha t ~ he loa d current is one ha lf of t ha t in t he
net w ork ust before t he sw it ch is opened.
The considera t ion of impeda nce-ma tching is of ext reme impor t a nce
in designing a line-t ype pulser be a use it a ffect s t he ut iliza t ion of t he
en ergy st or ed on t he net w ork, a s w ell a s t he ult ima te sha pe of t he volt a ge
a nd curr ent pulses a t t he loa d.
F or t hese rea sons, t he na ture of t h e loa d
must be know n before pr oceeding t o t h e design of t he pulser .
I f t he
loa d is nonlinea r , a s in t he ca se of a ma gn et ron, it ver y oft en ha ppens
t ha t t h e loa d cha ra ct er ist ics ca n be t a ken int o a ccount only a pproxi-
ma t ely, a nd t he ult ima t e design of t he n et w or k ma y ha ve t o depen d on
experiment a l t est s w it h subseq uent modifica t ions t o obt a in t he desired
pulse sha pe.
P ulse-forming n et w orks ca n be designed t o ha ve a ny va lue of cha ra c-
t er ist ic impeda nce, but ma t t ers of pra ct ica l convenience, such a s t he
a va ila ble size of induct a nces a nd condensers a nd t he ma ximum permis-
sible sw it ch volt a ge, oft en dict a te t ha t t is va lue be differ ent from t ha t
req uir ed t o ma t ch t h e impeda nce of t he loa d. When t he net w ork
impeda nce is differ ent fr om t h e loa d impeda nce, t he ma tched condit ion
is a t t a ined by t he use of a pulse t ra nsform er .
Aga in , for rea sons
of engineer ing convenience, it ha s been com mon t o a pply t he pulser
out put dir ect ly int o one end of a coa xia l ca ble t hus fa cilit a t ing t h e
physica l se a ra t ion of t he pulser a d t h e loa d. The impeda nce of t h e
ca ble ma t ches t ha t of t he net w ork, a nd a pulse t ra ~ sfor mer a t t he ot h er
end pr ovides t he impeda nce ma t ch t o t he loa d. S ince t he ca ble t ha t ha s
been most a va ila ble for a pplica t ions of t his t y pe ha s a ch a ra ct er ist ic
 
10 INTRODUCTION
[SEC. 1.4
fed lin~ type pulsers for m icrow a ve ra da r ha ve been designed for t h e
50-ohm level, t hereby ma king t he use of a pulse t ra nsformer a necessit y
w it h m a gnet r on loa d. The pulse t r a n sformer t h erefore becom es a n
essent ia l pa rt of t he discha rging circuit in a low -impeda nce pulser used
w it h high-impeda nce loa d, a nd a s such it s cha ra ct er ist ics ha ve a n effect
on t he pulse sha pe a nd t he over-a ll beha vior of t he discha rging cir cuit .
I t is desira b e a nd oft en necessa ry t ha t t he design of t he pulse t ra nsform er
a nd t he design of t he pulse-forming net w ork be coordina ted in or der t o
obt a in t he most sa t isfa ct ory pulser opera t ion.
S ince t he impeda nce-t ra nsforma tion r a tio for a t ra nsformer is equa l
t o t he sq ua re of t he volt a ge-t ra nsforma t ion ra t io, t h e use of a low -
impeda nce pulser w it h a loa d of higher impeda nce requires t he use of a
pulse t ra nsform er t ha t gives a volt a ge st epup bet ween pulser out put a nd
loa d input . Thus, w h en a line-t ype pulser w it h a 50-ohm volt a ge-fed
net w ork is used t o pulse a n 80&ohm loa d, for exa mple, t h e volt a ge
st epup ra t io is a bout 4/1, a nd t he cur ren t in t he discha rging circuit of
t he pulser becom es a bout four t imes t he loa d curr ent . Accor dingly , t h e
sw it ch in t h e discha rging circuit of a line-t ype pulser is req uir ed t o pa ss
very high pulse curr ent s for high pulse pow er int o t he loa d. S ince t h e
sw it ch is in ser ies w it h t he pulser out put , it s effect ive resist a nce must be
sma ll compa red w it h t he cha ra ct er ist ic impeda nce of t he pulse-forming
net w ork if high efficiency is desired.
When a pulser uses a volt a ge-fed net w ork, t he volt a ge a cross t h e
sw it ch fa lls t o zero a t t h e end of t he pulse beca use t he st or ed energy is
com plet ely discha rged. This consider t ion, in conjunct ion w it h t he
high cur rent -ca rr yin g ca pa cit y a nd low re ist ance req uired of t he sw it ch,
suggest s t he use of a for m of ga seous-discha rge device, w hich must rema in
nonconduct ing during t h e int erpulse int erva l if it is desired t o a pply a
succession of pulses t o t he loa d.
I it is a lso req uired t ha t t he i t erpulse
int erva ls be of cont rolled dura t ion, t h e sw it ch must h a ve a fur t her
cha ra ct er ist ic w hich a llow s a posit ive cont r ol of t he t ime a t w hich con-
duct ion is init ia t ed. These sw it ch req uirement s ca n be me by r ot a ry
spa rk ga ps, w hich depend on over volt ing by a decrea se in t he ga p lengt h,
or by fixed spa rk ga ps, in w hich t h e discha rge is init ia ted by a n a uxilia ry
elect r ode. A gr id-cont r olled ga seous-discha rge t ube such a s t he t hyra -
t r on is pa r t icula r ly w ell suit ed t this a pplica t ion since it is possible t o
st a r t t he discha rge in a t ube of t his t ype a t a ny desired t ime, w it hin a
very sma ll fra ct ion of a m icrosecond, by t he a pplica tion of P i oper volt a ge
t o t he gr id. S ever a l gr id-cont rolled hydrogen-filled t hyra tr ons of dif-
ferent volt a ge a nd current ra t ings t ha t cover t he ra nge of pulse-pow er
out put from a few kilow a t t s t o a lmost t w o mega w a t t s ha ve been devel-
oped for t his a pplica t ion. These h ydrogen t hyra t rons ha ve pr oved t o
 
11
q ua tely a ll t he sw it ch req uirement s ment ioned a bove a nd ha ve a st a bilit y
a ga inst a mbient t empera ture va r a t ions t ha t is considera bly bet t er t ha n
t ha t of t he mercury t hyra t ron . H ydrogen t h ra t rons t ha t ha ve a
sa t isfa ct ory opera t ing life a nd yet ca n hold off 16 kv w it h t he gr id a t
ca thode pot ent ia l a nd ca rry pulse current s of severa l hundred a mperes
for a pulse dura tion of 2 psec a nd a recurrence freq uency of 300 pps ha ve
been d eveloped a n d m a nufa ct ur ed.
The gr id-cont rolled high-va cuum t ube is not w ell suit ed t o erve a s
t he sw it ch in a low -impeda nce line-t ype pulser using a volt a ge-fed net -
w or k beca use of it s ra t her low ca t hode efficiency a nd rela t ively high
r esist a nce during t he con duct ion period. An oxide-ca t hode high-va cuum
t ube t ha t req uires 60 w a t t s of ca thode-hea t er pow er , for exa mple, ca n
ca rry a pulse current of a bout 15 a mp for a pulse dura tion of a few micro-
seconds, a nd under t hese condit ions, t his t ube present s a resist a nce of
perha ps 100 ohms t o t he circuit . A hydrogen t hyra t ron, on t he ot h er
ha nd, w it h eq uiva len ca thode-hea ter pow er ca n ca rry a pulse current of
a bout 300 a mp, present ing a n effect ive resist a nce t o t he circuit of a bou
on e oh m.
As st a ted previously , a line-t ype pulser using curren~ fe net w ork
req uires a sw it ch ca pa ble of ca rry ing a current a t lea st t w ice t ha t
desired in t he pulser loa d. The fur t her req uirement t ha t t his sw it ch
must be ca pa ble of int errupt ing t his current . a nd w it hst a nding high volt -
a ge during t he pulse elimina tes t he ga seous-discha rg t ype a nd point s t o
t h e gr id-con tr olled h igh -va cuum t ube.
Th e low cur rent -ca r ryin g ca pa c-
it y of exist ing t ubes ha s, t herefore, been t he principa l deciding fa ct or in
choosing t he volt a ge-fed n et w ork for line-t ype pulsers ra th r t ha n t he
cu r r en t -f ed n et w or k .
S ever a l d iffer en t m et h od s a r e u sed
t o cha rge a volt a ge-fed net w ork in a
line-t ype pulser . S ince t he genera l
a spect s of t hese met hods a re not a p-
pr ecia bly a ffect ed by t h e disch a rgin g
circuit , t he req uiremen ts im posed on
pulser design by t he cha rging circuit
ca n be considered sepa ra tely . I f t he
t ime a llow ed for t he c a rging of t he
n et w or k is su fficien t ly lon g com pa r ed
w it h t he pulse dura t ion, t he cha rging
cycle is simply t ha t corresponding t o
t he a ccumula t ion of cha rge on a con-
Isolating
element
Power
supply
a’
cuit for a voltage-fednetw ork.
denser. F igure 1.5 indic~ t es schema t ica lly t he rela t ion bet w een t he cha rg-
ing a nd discha rging circuit s of a pulser w it h volt a ge-fed net w ork.
F or
 
12
INTRODUCTION
[SEC.1.4
a high resist a nce, in w hich ca se t h e equilibrium volt a ge on t he net w ork
ca n be nea rly eq ua l t o t he pow er-supply volt a ge. The req uirement on t he
ser ies-resist ance isola t ing element in t his cha rging circuit is simply t ha t
it must be la rge enough t o a llow only negligible curr ent t o be t a ken from
t he pow er supply during t h e pulse a nd t he d io izing t ime for t he sw it ch,
but not so la rge t ha t t h e RC ime const a nt becom es compa ra ble t o t he
int erpulse int erva l. To get t he highest net w ork volt a ge from a given
pow er-supply volt age w it h t his a rra ngement , t he lengt h of t he int erpulse
int erva l should be severa l t imes gr ea ter tha n t he RC t ime const a nt in t he
cha rging circuit . This m et h od of cha rging t he net w or k is nherent ly
inefficient -it s ma ximum possible efficiency is only 50 per cen t .
S ince t he efficiency of t he net work-cha rging circuit w it h a resist a nce
a s t he isola ting elem ent is ver y low , t he use of a nondissipa tive element ,
such a s a n induct a nce, suggest s it self. When a ca pa cit a nce is cha rged
t hrough a n induct a nce from a const a nt pot ent ia source, t he volt a ge
a cross t he ca pa cit a nce is in t he form of a da mped oscilla t ion t he first
ma ximum of w hich is a pproxima tely eq ua l t o t w ice t he supply volt a ge if
t he init ia volt a ge a cross t he ca pa cit a nce a nd t he curr nt t hrough t h e
induct a nce a re zer o. his ma ximum occur s a t a . t ime eq ua l t o z ~
a ft er t he volt a ge source is conn ect ed t o t he induct a nce-ca pa cit a nce
combina t ion. The induct a nce t o be used w it h a given net w ork is, t h ere-
fore, ca lcula t ed by set t ing t he int erpulse int erva l eq ua l t o T ~ , w her e
C is t he net w or k ca pa cit a nce. This t ype of n et w ork cha rging is ca lled
“resona nt cha rging.” I f t h e pulse r ecurr ence freq uency is less t ha t
l/r ~ , some current w ill st ill be flow ing in t he induct a nce a t t h e
beginning of ea ch cha rging per iod a nd, under equilibr ium condit ions, t his
init ia l current w ill be t he sa me for a ll cha rging cycles. The net w or k w ill
.
t ype of net w ork cha rging is ca lled “linea r cha rging. ”
Wit h ca reful design of t he induct a nce, t he efficiency of t he cha rging
circuit is a s high a s 90 t o 95 per cent , a nd t he pow er-supply volt a ge needs
t be only slight ly grea ter t ha n one ha lf of t he desired net w ork volt a ge,
result ing in a gr ea t a dva nt a ge over resist a nce cha rging. A fa ct or of 1.9
t 1.95 bet w een net w ork a nd supply vo t a ge ca n be obt a ined if t he
cha rging induct a nce is designed so t ha t t e q ua lit y fa ct or Q of t he cha rg-
in circuit is high.
Resona nt cha rging ca n a lso be done fr om a n a -c source provided
t ha t t he pulse recur ren ce freq uency, P RF, is not grea t er t ha n t w ice t h e
a -c frequency. I f t he pulse r ecur ren ce freq uen cy a nd t he a -c freq uency
a re equa l, t he net w or k volt a ge a t t a ins a va lue r t imes t he pea k a -c volt -
a ge. This volt a ge st epup becomes grea ter a s t he ra tio of a -c freq uency
t o pulse recur ren ce freq uency increa ses. The volt a ge ga in soon becomes
expensive, how ever , a nd it is not pra ct ica l t o go beyond a n a -c freq uency
 
13
1.5, A C ompa rison of H a rd-t ube a nd Line-t ype P ulsers.—Alt hough
it is not possible t o give a set of fixed rules t o be follow ed in det ermining
t he t ype of pulser est suit ed t o a pa rt icula r a pplica tion, it is possible t o
give a few genera l compa risons of t he t w o t ypes w hich ma y a id in choos.
ing bet w een t hem. The com a risons ma de here concern such t hings a s:
pow er out put a nd efficiency, pulse sha pe, impeda nce-ma tching, short
in t erpulse int erva ls, high-volt a ge versus low -volt age pow er supply, t he
ea se w it h w hich pulse dura t ion a nd pulse recurrence freq uen y ca n be
cha nged, t ime jit t er , over-a ll circuit complexit y , size a nd w eight of t he
pulsers, a nd regula tion of t he pulser out put a ga inst va r a tions in input
volt a ge. This list does not include a ll t he possible poin t s for compa ri-
son, but only t hose t ha t a re of prima ry impor t a nce in choosing bet w een
t he t w o pulser t ypes.
The over-a ll efficiency of t he line-t ype pulser is genera lly somew ha t
highe t ha n t ha t of t he a rd-t ube pulser , pa r t icula r ly w hen t he pulse-
pow er out put is high. This is due in pa r t t o t he fa ct t ha t t he ha rd-t ube
pulser req uires a la rger overhea d of ca thode-hea ting pow er . Furt her-
more, a h igh-va cuum-t ube sw it ch dissipa t es a grea t er port ion of t he
a va ila ble pulser pow er by vir t ue of it s h igher effect ive resist a nce t ha n
does a ga seous-discha rge sw it ch . The pow er required for t he dr iver of
t he ha rd-t ube pulser is not negligible a nd, since t his component is not
necessa ry in a line-t ype pulser , t he over-a ll efficiency of t he la t t er is
t h er eb y en h a n ced .
The pulse sha pe obt a ined from a ha rd-t ube pulser ca n usua lly be
ma de more nea rly , rect a ngula r tha n t ha t from a line-t ype pulser . This
is pa rt icula rly t rue w hen t he net w ork of t he pulser ha s low impeda nce,
a nd a pulse t ra nsformer must be used bet w een t he pulser a nd a nonlinea r
loa d such a s a ma gnet ron. In t his ca se, sma ll high-freq uenc oscilla -
t ions a re superimpose on t he volt a ge pulse a t t he loa d. These oscil-
of t he corresponding oscilla tions on t he t op of t he current pulse depends
on t he dyna mic resist a nce of t he loa d a nd, if t his is sma ll, t hese oscilla -
t ions become a n a pprecia b e fra ct ion of t he a vera ge pulse a mplit ude.
The ha rd-t ube pulser is, t herefore, genera lly preferred t o t he line-t ype for
a pplica tions in w hich a rect a ngula r pulse sha pe is import a nt .
Impeda nce-ma t ching bet w een pulser a nd loa d ha s a lrea dy been
ment ioned a s a n import a nt considera tion in t he design of line-t ype pul-
S S rs. U sua lly, a n impeda nce misma tch of ~ 20 t o 30 per cent ca n be
t olera ted a s fa r a s t he effect on pulse sha pe a nd pow er t ra nsfer t o t he loa d
k concerned, but a grea ter misma tch ca uses t he over-a ll pulser opera t ion
t o become unsa tisfa ct ory. The loa d impeda nce of t he ha rd-t ube pulser ,
how ever , ca n be cha nged over a w ide ra nge w it hout seriously a ffect ing
t he opera t ion . The principa l limit a t ion in t he la t t er ca se is t ha t , if t he
 
[SEC. 1.5
is l:irge :in(l t h e pow er dissipa ted in t he sw it ch becomes a la rger fra ct ion
t )f t he t {J t:d po\ rcr , t hus lo rer ing t he efficiency.
In a pplica t ions of t he
I inu-t ypr pulser it is possible t o effect a n impeda nce ma t ch for a ny loa d
by t he proper choice of pldse t r :msfurmcr , but t his procedur e is sorneu-ha t
inconvenient if, for exa mple, it is desire t o va r y t he po~ ver input t o a
nonlinea r loa d bct jveen }vidc limit s.
S \vit chcs of t he ga seous-discha rge t ype, ~ vhich a re commonly used in
t he line-t ype pulser , pla ce a st r ingent limit a t ion on t he minimum spa cing
bC t \ YC C I lulses. Aft er t h e pulse, t he net \ rork must n ot cha rge p t o a ny
a pprecia ble volt a ge unt il t h e deioniza t ion is complet e, ot her w se t he
slvit ch ]~ ill rema in in t he conduct ing st a te a nd t he po ver supply \ vill be
short -cirmlit cd. For t his rea son, t he int erpulsc int erva l must be severa l
t imes :1s long M t he slr it ch deioniza t ion t ime \ vhcn t he ga seous-discha rge
t ype is (MY1. ‘l’h e high-va cuum-t ube s\ vit ch in t he ha rd-t ube pulser does
not , prm ent a ny simila r limit a tions on t he int crpulsc int erva l, but in t his
ca se t he problcm bccomcs on e of designing t he circuit ~ vit h sma ll RC a nd
1./1/ t ime const a nt s. I t ha s been possible, for exa m ple, t o const r uct
ha r(l-t ube pulsers \ vit h 0,2-~ sec pulses spa cccl 0.8 ~ s ec bet ~ reen lea ding
edges,
I t ha s been st a t ed in t he preceding discussi n of ha rd-t ube pulsers
t ha t a high-volt a ge po\ vcr supply is necessa ry for highe t efficiency .
‘I ’his rcq uircr ncnt is somet im es a ver y ser ious limit a tion on t he design of
su ch pu lscr s for h igh -pu lse-polvcr ou tpu t.
Th e low -ir n pcd a n ce lin e-t y pe
pulser using resona n t cha rging of t he net w or k, on t he ot her ha nd, ca n be
designed w it h a much lolrer pow -er-supply vol a ge for a pulse-pow er
out put compa ra ble t o t ha t of a ha rd-t ube pulser . For exa mple, a ha rd-
t ubc p lscr \ vit h a pulse-po~ vcr out put of 3 MW ha s been built w it h a
3 -kv po~ r er sllpply, ~ vhcr ca s for a lin e-t ype pulser w it h d-c resona nt
cha rging of t he net \ vor k, t he sa me po\ \-er out put is obt a ined w it h only
a bout 14 kv from t he pofvcr supply if a st a nda rd 50-ohm n et vor k is used.
,~ line-t ype pulscr using a -c resona nt cha rging, on t he ot her ha nd, requires
a n a -c po\ ~ m source giving a pea k volt a ge of a bout 8 kv in order t o provid
a pulse-po\ rcr out put of 3 31w .
I t should bc st a t ed, h o~ vever , t ha t in
bot h of t he line-t ype pulscrs ment ioned here t he pulse-forming net w or ks
a rc cha rged t o a bout 25 kv, but t his volt a ge does n ot present such serious
design problem from t he engineering st andpoint a s t he design of a pow er
supply of equiva lent volt a ge. I t J vould ha ve been a dva nt a geous t o
ha ve a poi~ -cr-supp]y volt a ge gr ea t er t ha n 35 kv for t his 3-MJ v ha rd-t ube
pulsrr , I )llt a h igher volt a ge \ va s impra ct ica l beca use t he pulscr design
NW limit ed by t he a va ila ble com ponen t s, in pa r t icula r by t he s\ vit ch
tul)e.
[t is somct irncs desira ble t o ha ve a pulscr ca pa ble of producing pulses
 
by a simple sw it ching opera t ion.
The pulse dura tion is det ermined in
t he dr iver of t he ha rd-t ube pulser , w here t his t ype of pulse select ion is
ea sily ma de since t he sw it ching ca n be done in a lo~ v-volt a ge pa rt of t he
circuit . In t he line-t ype pulscr , holvcvcr , t he pulse dura tion is det er-
mined by t he net lvork a nd in order t o cha nge t he pulse dura t ion a different
net w or k must be connect ed int o t he circuit .
This ca n be a ccomplished
by a sw it ching opera tion, but beca use of t he higher volt a ge involved it is
not so simple a s in t he ha rd-t ube pulser .
A fur t her complica tion ma y
a rise in t he line-t ype pulser since a cha nge of net w or k a ffect s t he cha r a ct er -
ist ics of t he cha rging circuit , a ncl pra ct ica l considera t eions of induct a nt e
cha rging t herefore limit t he ra nges of pulse dura tion a nd pulse recur-
r ence freq uency t ha t ca n be covered. The ea se w it h w hich t he pulse
dura t ion ma y be cha nged in a ha rd-t ube pulser provides a flexibilit y t ha t
is difficult t o obt ain w it h a line-t ype pulser .
In ma ny pulser a pplica t ions it is impor t a nt t o ha ve t he int erpulse
in terva ls precisely determined .
In ha rd-t ube pulsers a nd some line-t ype
pulsers, const ant int erpulse int erva ls a re obt a ined by using a t rigger pulse
t o init ia t e t he oper a tion of t he pulser .
These t rigger pulses ca n be gener-
a ted in a low po~ rer circuit independent of t he pulser , a nd it is a simple
ma t t er t o design such a circuit so t ha t t he t r igger pulses occur a t pre-
cisely know n t ime int er va ls.
l~ hen t he successive out put pulses from
t he pulser st a r t w it h va rying t ime dela y a ft er t he st a r t of t he t r igger
pulse, t her e is sa id t o be t ime jit t er in t he out put pulses. I f t he t r igger
pulses a re used t o init ia t e t he opera t ion of ot her a ppa ra t us, w hich is
a uxilia ry t o t he pulser , t his t ime jit t er result s in unsa t isfa ct ory over-a ll
opera tion ot ’ t he eq uipment . H a rd-t ube pulsers ca n be ea sily designed
t o ma ke t his t ime jit t er negligible, t ha t is, = 0.02 gsec or less. The t ime
jit t er is a lso sma ll in line-t ype pulsers t ha t ma ke use of a hydrogen t yra -
t r on a s t he s vit ch. lVit h line-t ype pulsers using t he t r igger ed spa rk
ga ps (ser ies ga ps), how ever , t he t ime jit ter is considera bly grea t er , a bout
0. t o 3 K scc depending on t he ga p design. Recent development of a
t riggered spa rk ga p ha ving a ca thode consist ing of spongy iron sa tura ted
w it h mercury ha s ma de it possibl t o obt a in t ime jit t er a s sma ll a s 0.02
ps ec w it h t h e s er ies-g a p sw it ch .
t Vhen a rot a ry spa rk ga p is used a s t he
sw it ch in a line-t ype puker , t he int erpulse int e va ls a re det ermined by
t he rot a t iona l speed a nd t he number of spa rking elect rodes. In t his
ca se t ime jit t er refers t o t he ir regula rit y of t he int erpulse int erva ls a nd
ma y a mount t o a s much a s 20 t o 80 ysec.
B eca use t he circuit for t he ha rd-t ube pulser is somew ha t more com-
plex a nd req uires a la rger number of sepa ra t e component s t ha n t ha t of
t he line-t ype pulser , bot h t he problem of servicing a nd t he dia gnosis
of fa ult y beha vior of t he ha rd-t u e pulser a re more difficult . B eca use of
 
[S E C .I 5
I inc-t ype pukw r ca n genera lly be designed fo sma ller size a nd w eight t ha n
a ha rd-t ube pulser \ vit h eq uiva lent pulse- a nd a vera ge-po\ ~ er out put a nd
w it h compa ra ble sa fet y fa ct ors in t he individua l component s.
TAB LE1 1.—C OMP ARI S ONF THETw o P U L S E RTYP E S
Characterist ics
J Miciency. . . . . . . . .
P u l s e s h a p e . . . . . . . . .
Impedarl{:c-rllatching
Cha ngeof pulseclura.
voltage
requiredfor the driver ,ca th-
ode-hea t ing,a nd for dissipa .
t ion in t h e s w it ch t u be
Betterrectangularpulses
missible
Ma y be ver y s hor t ; a s for cod
in g bea con s (i.e., < 1 ps cc)
High-vol tage supply usual ly
necessary
circuit
S omew ha t ea sier t o obt a in
n egl g ible t im e jit t er (i.e.,
< 0.02 psec) t ha n w it h a
line-typepulser
~ r ea t cr , lea ding t o grea t er
diff iculty in servicing
F or d es ig n h a vin g m a xim um
cfficicncy, (AP /P ) output =
ficingefficiencyin t he design,
(t i’/~ ) ou t pu t = 0.5(AV/V
in pu t ca n be ob t a in ed
Line-ty pe pulser
t figh , pa r t icula r ly w h en t he
pulse-po,verout put is high
per missible ( + 20 t o 3070).
P ulset ra nsformerwill ma tch
a n y loa d , but pow er in put t o
nonlinea r loa d ca nnot be
va r ied ov er a w id e r a n ge
Must be severa l t imes t he
deioniza tion t ime of dis-
char getube (i.e. , > 100@cc)
Low-volta ge supply , par t icu-
la r ly w it h in du ct a n ce ch a r g -
in g
Requires high-volta ge sw itch-
in g t o n ew n et w or k
lligh-pOw er line-type pulsers
w it h r ot a r y -ga p s w it ch h a ve
a n inherent lyla rgetimejit ter;
w it h ca re in design a nd t he
use of a h ydr ogen t hy ra t ron
or en clos ed g a ps of m er cu r y -
spon ge t ype, a t im e jit t er of
0.02 ~ ec is obt a in a ble
L es s, per m it t i ng s m a ller s iz e
a n d w e ig ht
B et t e r t h a n a h a r d -t u be pu ls er
d es ig ned for m a xim um effi-
cien cy s in ce (A~ /~ ) ou t pu t
= 2(AV/V) in put for a lin e-
t y pe pu ls er , in depen den t of
the des ign
The effect on t he pow er out put of pulser result ing from a cha nge in
t he input volt a ge is somet imes of considera ble impor t a nce t o t he pa rt icu-
la r a pplica tion. F or a line-t ype pulser , t he percent a ge cha nge in out put
 
S E C .1.5]
lit t le ca n be done t o cha nge
COlfPA RISON
17
.
ha r d-t ube pulser , hoir evw , t his ra t io m~ y be cont ro led by t he pr oper
choice of t he s vit cb t ube a nd it s opera t ing condit ion s.
Th e per cen t a g e
cha nge in out put polver from a ha rd-t ube pulser ma y be va ried over t he
ra nge of 0.5 t o 6 t imes t he per cent a ge cha nge in input line olt a ge.
This
a dv nt a ge w it h t he h a rd-t ube pulser is ga ined only a t t he expense of
low er efficiency , hoircver , a nd t he ra tio is la rge w hen t he discha rging
cir cu it is design ed for m a xim um efficien cy .
These compa r isons bet w een ha r d-t ube a nd line-t ype pulsers a re
summ arized in Ta ble 1’1.
I t should be eviden from t h ese genera l rem a rks con cernin g t he rela -
t ive mer t s of ha rd-t u e a nd line-t ype pulsers t ha t a per fun ct or y a na lysis
of t he req uir ement s for a pa rt icula r a pplica t ion ca nn ot lea d t o a n int el-
ligent ch oice of t he pulser t ype t o be used.
A det a iled a na lysis r eq uires a
t horough underst a ndin g of t he cha ra ct er ist ics of pulsersin gener a l, a nd
of t he t w o t ypes in pa rt icula r .
I t is t he pur pose of t he follow ing cha pt ers,
t h er efore, t o pr esen t t h e a va ila ble informa tion on ha rd-t ube a d line-
t ype pulsers in considera ble det a il in or der t ha t it m a y be of t he grea t -
est possible a id in t h e design of h igh-pow er pulse genera t ors for a ny
application.
C H AP TE R 2
TH E OU TP U T C IRC U I T OF A H ARD -TU B E P U L S E R
B Y G . X. G I ,.+ SOE
2.1. Th e B a sic Out put C ircuit . —Asst a t ed in C h a p. l, pulse-gen era t or
drsign a nd opera tion a re discussed h ere from t h e st a ndpoint of t h e ba sic
cir cuit sh oiy n in I ~ ig. 1.1, t he essen tia l elem en ts of }Vh ich a r e t he r eser voir
forclcct r ica l crw rgy , t h e sin-it ch , a nd t h e loa d. Th ese com pon en t s con -
st it ut e t he o[lt put circuit of t he pulser, a n dt heir iuh eren t cha ra ct er ist ics,
t ogct hm \ vit ht he circuit beh a vior , a lmost exclusively det erm in e t he pulse
sha pe a nd a mplit ude. Th e pow er out put from a pulser is usua lly
rrq nired t o be a succession of pulses occurr in ga t m or e orless regula r t im e
int erva ls w it h a specified t im e dura tion for ea ch pulse.
Th e com plet e
pulser circuit must t her efore cont a in , in a ddit ion t o t he out put circuit , a
mums of con t rollin g t h e ura t ion of t h e pulse a nd of replen ishing t h e
dect rica ] rn crgy in t he reser voir durin g t he int erpulse int erva ls.
Since
t he plI lsc s ha pe a nd a mplit ude a re usua lly t he m ost import a nt ch a ra ct er-
ist ics of t h e pulscr out put , it is logica l t o begin t h e discussion w it h a con -
sidera t ion of t he out put circuit .
‘1’hch a rd-t ube pn lser der ives it s na me from t he fa ct t ha t t he sw it ch is a
lligh-vt icn~ lmt ulw , t he con duct ion t h rough ~ r hich ca n b con t rolled by
t h o a ppli~ a tion of t h e pr oper volt a ge t o a gr id. In it s simplest form such
:1sjr it ch is a t rioflc, l)llt , a s is sllo\ rn la tcrl a t et rode or pen t ode ca n oft en
pcrfn rm t h e s\ vit ching flln ct ion m or e sa tisfa ct orily . The ch oice of t h e
t llhc t o bc usrd a s t h e slr it ch in a pulser designed for high pulse-pow er
on t put drpcn(ls on t h e ca p~ bi]it y of t h e t ubc t o pa ss high pea k current s
a nd t o st a nd off high volt a grs. Th e volt a ge drop a cross t h e sw it ch t ube
must a lso be con si(lcrcd in con n ect ion w it h over-a ll pulser efficiency
w rd a llo\ ra lllc p ow er dissipa t ion in t he t ube, pa rt icula rly if t he dut y ra t io
for t hr pn lscr is high. Th e cliscussion of t he design of h a rd-t ube pulsers is
t h er efore influen ced t o a considera ble ext en t by t h e cha ra ct er ist ics of
t he high-va cuum t ubes t ha t a ve been a va ila ble.
Condm,wr as the Energy Rrsm’oir.-The r eser voir for elect rica l en er gy
in a t ,a rd-t U be pulser ma y be eit h r a con den ser or a n in duct a nce.
Th e
h :m l-t llbr pulser s for m icr o va ~ ’e-r a da r a pplica t ion s h a ve m ost com mon ly
hrcn of t h r con den ser t ype.
The t w o possibilit ies ma y be represen t ed
sch ema t ica lly a s sh ow n in F ig. 2.1, w her e t h e loa d is in dica ted a s a pure
resistance.
In F ig. 2. la s]vit ch (1) is in t roduced on ly for con ven ien ce
21
THE OUTPUT CIRCUIT OF A HARD-TUBE PULSER [SEC.21
in t he present discussion a nd is repla ced by a high-impeda nce element in
t he m or e clet a iled discussion in t he follo~ v in g sect ions.
Assume t ha t t he sivit ch (1) in F ig. 2. la is closed long enough t o a llow ,
t he condenser t o be ome cha rged t o t he po~ ver-supply volt a ge. An
a mount of energy ~ CJ l~ is t hen a va ila ble t o be discha rged in t o t he loa d
‘EEfa
a)
(b)
I’,,., ?.l. -– lhic ha rd -t ubepula ercircuits .
(a) TI ,c CCI , ICICIMETy pe. (h ) Th e i ,d uct m ce
type.
l)y ,J p,,ning s~ r it ch (1) a nd closing s\ vit ch (2). D uring t his condenser dis-
t ,l):t rgc, t he volt a ge a cross t he loa d decrea ses \ rit h t ime a ccording t o t he
]{,l:ttion
~ 1 = E bbe– (R I + ~ P J C - – VP ,
ivh er c t is mea sured from t he inst a nt t he sw it ch is closed, a nd Vp = Zpr p is
t he volt a ge drop in t he s\ ritch. I f t he s\ vit ch is closed for a t ime sma ll
cl)rnp:w cd Irit h t he t imc const a nt (R+ rP )C ~ , only a sma ll pa rt of t he
t t ka l energy st ored in t he condenser is removed, a nd t he volt a ge a cross
t h c loa d a nd t he current t hrough t he slvit ch a rc very nea rly const a nt .
‘1’he loa d is t herefore subject ed t o a volt a ge pulse of dura t ion correspond-
ing t o t }m engt h of t ime t he s\ vit ch is kept closed. The ca pa cit a nce t ha t
is nec(w a ry t o keep t he pulse volt age bet lveen t he limit s VI and VJ — AVI
(,:111(,a sily be ca lcula ted if t he pulse current a nd t he pulse dura tion a re
s l)ccil i(, (l.
I f t he puke dura t ion T is a ssumed t o be sma ll compa red Wit h
t ,lw fW t ime const a nt of t he discha rging circuit , t he cha nge in volt a ge of
t llc ooudenser during t he pulse ma y be w rit t en
AV1 = T.
w
If s\ ~ it ch (1) is closed a ga in for t he t ime bet ween pulses, a ft er opening
in t he condenser is replenished from t he pof~ er
Sllpply.
.1 repet it ion of t his sw it ch ing procedure produces a succession
of ident ica l pulses.
The import a nt point of t his discussion is t ha t t he
sir it ch t ube, represent ed by s~ vit ch (2), ca rr ies curren t only during t he
pulse int erva l. H ence t he a vera ge po~ ver dissipa t ed in t he sw it ch t ube is
 
23
t he pulse dur a tion , a n d T , = 1/, is t he recurren ce int erva l. The pow er
dissipa ted in t he sw it ch t ube is a ugment ed slight ly by repla cing sw it ch
(1) by a high-impeda nce element , but f r t he present considera t ions this
increa se ma y be neglect ed. Figure 2.2 show s a sket ch of t he conden-
ser v olt a ge a s a funct ion of t ime w hen sw it ch (1) is repla ced by a high
resistance.
F I G .22.-Ideal ized sketchof the t imeva ria t ionof the vol tageon the stora gecondenser
in a ha rd-tubepulser.
Inductan e as t he E ner gy Reser voir .—C on sider n ext t he pulser r epr e-
sen ted in F ig. 2. lb, in w hich a n induct a nce serves a s t he elect rica l-energy
reservoir . When t he sw it ch is closed, a current builds up in t he induct -
a n ce a ccor din g t o t h e r ela t ion
w here rP , t he effect ive resist a nce of t he sw it c , is considered t o be sma ll
com pa r e d w i t h R~, a nd t he resist a nce of t he induct a nce is a ssumed t o be
negligibly sma ll. I f t he sw it ch is opened a t a t ime t1,he init ia l cur ren t
in t he loa d resist ance is iL(~l) a nd decrea ses w it h t ime a ccording t o t he
relation
–3’
il(t ’) = iL(t l)e ‘w
w heret is mea sured from t he inst ant of opening t he sw it ch.
I f t l >> L ~ /Tp,
t he init ia l volt a ge a cross t he loa d is E M RI / T p. A pulse is produced by
keeping t he sw it ch open for t he t ime int erva l desired for t he pulse dura -
t ion. I f this t ime is sma ll compa red w it h L ~/ R t, t he current in t he induct -
a nce, a nd hence t ha t in t he loa d, decrea ses only slight ly during t he pulse,
a nd a la rge fra ct ion of t he energy init ia lly st ored h t he induct a nce is
st ill t here a t t he insta nt t he sw it ch is clo ed. As a result , t he current in
t he sw it ch a t t he st a r t of t he int erpulse int erva l is a lmost a s la rge a s it
w a s a t t he st a r t f t he pulse. I f a succession of pulses is obt a ined by
repea t ing t he sw it ching procedure, t he a vera ge current t hrough t he
sw it ch t ube is n ea rly eq ua l t o t he pulse curr en t.
Com par i son of a Condenser and an I nductanc~ as the Ener gy Reser -
voir .—The pulse curre t t hrough t he sw it ch t ube for a given pulse pow er
int o a loa d is t he sa me w het her t he elect rica l en ergy is st or ed in a n in duct -
 
[S E C .2.1
I
t ube is com pa ra ble in t h e t w o ca ses.
Th e a vera ge pow er dissipa ted in
t h e sw it ch t ube, h ow ever , is much h igh er w h en a n induct a n ce is used
beca use t h e t ube is on duct in g durin g t h e in t erpulse int erva l, w herea s,
w hen a ca pa cit a nce is used, it is con duct in g on ly durin g t he pulse in t erva l.
Th e idea lized sket ch sh ow n in F ig. 2.3 in dica tes t he cur ren t in t he in duct -
- —-----------
- .---—---- .
-
FIG .2.3.—Idealizedsketchof th e time varia t ionof currentin th e storageinducta nceof e.
ha rd -t ubepulser.
Alt hough t h e pow er-supply volt a ge req uired for a pulser w it h a n
in duct a nce for en er gy st or a ge is considera bly less t ha n t h e desired pulse
volt a ge a cross t h e loa d, t h e sw it ch t ube must be ca pa ble of w it hst a ndin g
a pproxim a t ely t h e sa me volt a ge a s w h en a ca pa cit a n ce is used. I n a
pulser of t h e t y pe sh ow n in F ig. 2. la , t h e ma ximum volt a ge a cross t h e
sw it ch t ube is eq ua l t o t h e pow er-supply volt a ge, w h ich m ust be grea ter
t ha n t h e loa d pulse volt a ge by a n a moun t eq ua l t o t h e volt a ge d op in
t h e t ube. Th e ma ximum volt a ge a cross t h e sw it ch t ube in t h e circuit
of F ig. 2“ lb is eq ua l t o t h e m a gnit ude of t h e pulse volt a ge plus t h e pow er -
supply volt a ge. P ulsers of t h e t w o t y pes t ha t a r e design ed t o give t h e
sa me out put volt a ge a nd curren t for a pa rt icula r loa d t h er efor e req uir e
a pproxim a tely t he sa me ch a ra ct er ist ics for t he sw it ch t ube.
I f t h e effect ive resist a nce of t h e sw it ch t ube is r educed, t h e a vera ge
pow er dissipa t ion in t h e in duct a n ce pulser becom es a less ser ious m a t t er .
A t ube of t h e ga seous-discha rge t y pe is ca pa ble of con duct in g a high
curr en t w it h a ver y sma ll volt a ge drop a cross t h e t ube, a n d h en ce int ro-
duces a low effect ive resist a nce in t o t he circuit . Wit h con ven t ion a l t ubes
of t h is t ype, h ow ever , on ce t h e ga seous disch a rge is init ia ted it ca nnot be
xt in guish ed by a pplica t ion of volt a ge t o a gr id.
F or t his rea son , t h e
kn ow n ga seous-discha rge t ubes a r e n ot pra ct ica ble sw it ch es for t he induct -
a n ce pu lser .
Th er e is a m et h od by w h ich t h e en er gy dissipa t ed in t h e sw it ch t ube
ca n be r educed t o a rea sona ble va lue in spit e of t h e rela tively high effec-
t ive resist a nce of h igh -va cuum t ubes. Th e m et h od is t o a llow a ll t h e
en er gy st ored in t h e induct a nce t o be disch a rged in t o t h e loa d before t h e
sw it ch is closed a ga in . As a result , t h e pulse cur ren t drops t o zer o a nd
t h e pulse sha pe, in st ea d of bein g rect a ngula r, ha s t h e form
–3’
23
Th e a ver a ge pow er dissipa tion in t he sw it ch t ube is kept sma ll by closin g
t h e sw it ch for on ly a sh ort t im e int erva l befor e t h e st a r t of t h e pulse.
Th e curr en t in t h e in duct a n ce a s a __
fun ct ion of t im e is sh ow n in F ig. 2.4.
Th e undesira ble n on rect a ngula r
puke ca n be t ra nsformed in t o a r ec-
t a ngula r pulse by m a king t h e in-
duct a n ce a pa r t of a cur ren t -fed
g
S w it chube
S w it chube
nonconducting
conducting
sibilit y is d iscu ssed in d et a il in C h a p.
FI G .2.4.—In ductmcecurr enta s a func-
6, w here it is sh ow n t h a t w it h such
t i on of t im e w h e n a l l t h e en er g ys t or ed in
a n a rra ngem en t t h e pulse cur ren t
th e inducta nceis discha rgedinto th e loa d.
in t h e loa d is on ly on e ha lf of t h e curr en t built up in t h e in duct a nce.
Th e a ver a ge pow er dissipa tion in t h e sw it ch t ube is t h er efor e reduced a t
t he expen se of a h igh er pulse-curren t r eq uirem en t on t he t ube.
B eca use of t h e pr ecedin g con sidera tions a nd t h e cha ra ct r st ics of
conven t ion a l h igh -va cuum t ubes, t h e con den ser w a s ch osen a s t h e elec-
t r ica l-en ergy r eservoir for a ha rd-t ube pulser . A det a iled discussion of
t he pulse sh a pe obt a ina ble w it h such a pulser must in volve t he pa rt icula r
ch a ra ct erist ics of t h e loa d a nd of t h e sw it ch t ube.
Th er e is in va r ia bly
som e dist ribut ed ca pa cit a nce a cross t h e loa d w h ich m ust be t a ken in t o
a ccoun t w hen con sider ing t h e sh a pe of t h e lea din g a nd t ra ilin g edges of
t h e pulse. I f, for exa m ple, t h e loa d is a bia sed diode, a con duct in g pa t h
must be p ovided in pa ra llel w it h t h e loa d in or der t o a llow t h e st ora ge
con den ser t o be r ech a r ged .
In t h e follow in g sect ions t h e possible a rra ngem ent s for t h e pulser
out put circuit a xe discussed, w it h empha sis on t h e effect of t h e va rious
circuit pa ra met ers on t h e sha pe of
I I
T
t h e out put pulse a nd on t h e effi-
Cw
1
RI
TH E D IS CH ARG I NG OF TH E
S TO RAG E C O ND E N S E R
Vg
=
+
 
Fm 2.&-Ha rd-tube pulserw i th a tr iodem
era t or ha s been em pha sized a nd
theswi tchtube.
rea son s h a ve been given for ch oos-
in g a con den ser t o ser ve a s such a
r eser voir in a h a rd -t ube pulser .
A pulser of t h is t y pe is a ct ua lly a C la ss C
a m plifier w h ose cou plin g con den ser is con sid er ed t o be t h e en er gy r es er voir ,
a s becom es eviden t w hen t h e circuit of F ig. 1.2 is r edra w n w it h a t h ree-
 
THE OUTPUT CIRCUIT OF A HARD-TUBE PULSER [SEC.2.