Phase modulator with tuned variable length electrical lines including coupling and varactor diode circuit

Brown, K. H.

Fitting, R. C.

English

NASA Technical Reports Server

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NATIONAL AERONAUTICS AND SPACE ADMINISTRATION 1 
WASHINGTON, D.C. 20546 
us~/scientif  i c  61 Technical Inf onnation Divi~ion 
Attentions Miss Winnia M. Mozgan , 
~ ~ / o f f i c e  of A s s i s t - t  General Counsel for 
Patent Matters 
, 
SUBJECT: Announcement of NASA-~wned U. S. Patents i n  STAR 
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I n  accqrdance with the procedures agreed upen by Code GP 
and Code USI, the attached NASA-owned U. S. Patent is beinq 
forwarded Eor abstracting and announcenrent in  WASA STAR. 
The following infomation is prwidedt 
U. S. Patent No. 
Government or 
~or'porate Employee 
Supplementary Corporate . I  
Source (if  applicable) t 
NASA Patent Case No. t Awe -1 - ?2#/"/ 
NOTE - If th is  patent covers an invention made by a 
employee of a NASA Contractor, the following i s  
yes NO U 
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Space ~ c t ,  the name of the Administrator of NASA appears oil I 
the first page of the patent; however, the name of the actua 
inventor (author) appears a t  the heading of Column No. 1 of 
the Specification, following the words a. . . w i t h  respect t 
Enclosure 
u (NASA CR OR TM OR AD NUMBER) (CATEGORY) 2 
https://ntrs.nasa.gov/search.jsp?R=19710018953 2020-03-17T03:14:31+00:00Z
PATENTED HAT 1 8 I971 
l NVENTORS 
KENNETH H. BROWN 
ROBERT C. F ITTING 
BY 
q-/ 
United States Patent 
1721 inventors Kenneth HI. Brow 
mwix; 
Robert C .  F i w ,  b t M a l e ,  A&. 
12 1 1 Appl !Vo. 789.903 
[22] Filed Jan. 8, 1969 
1453 Patented Nlay 18,1971 
I731 Assignee The e'nited States of America as represented 
by the Wdmi&&ator of the Nationral 
Aeromutia and Space Administration 
(541 P H S E  MOEbULATOW 
4 Cl~aiens, 1 ma* Fig. 
k521 US. Cl .................................................... 332129, 
332136 
[5l]  lint.C1 ........................................................ W03c3/L2 [so] ~ i e i d  on Search ......................................... 33 1/36 (c), 
177 (V);  332/29,30,30 IV),  43; 333/31,70 (B) 
1561 Refemnms Cited 
D STATES PATENTS 
3,400,342 911968 Putnam ....................... 33.31'3 i 
......................... 3,440.570 411969 Kasper 333;11X 
Primary Examiner-Roy 1-alte 
ASsiSl~nt Examiner-Lawrence 9. I)%& 
Attormy-Mueller, Aichele and Raunex 
m m C T :  A pair of tuned lines are coupled t r ~  a c~r i i c r  
signal source and a load through a quarter-laawe codpler The 
electical length of the lines are electricalsBHy altered to p k ~ ~  
modulate the carrier supplied by the source through the cou- 
pler to the toad. Varzctor dlodes and a vdraabie lndaictancc in 
each of the lines vary the line electrical lengths s ~ b z  that there 
is a iinear modulation of the carrier. The arraqgenlerrt ss sercb 
that the energy reflected from the two hnes ha*e phases op 
posing at the source such that there is no povirn s~~ppiled at L ~ C  
input coupler p r t  while all of the reflectesli p,iwer from *IT-, 
twe, lines is sqplieed in phase through the coa~l;ker cpi~aout i i r  I r 
to the load. 
3,579,147 
1 2 
P W E  MODULATOR Since the sngnals at port 12D are an-phiasc. qnan mum p,r2~~ - 
modulated RF energy IS supplied to ioc?d 11 11: m3j 5-c ni:glb~~td 
BBCKGROUND OF THE BMVEmBON that the configuratnon is syrnrnetrtcal In accocoarice t$z:ew~ib 
mns inQentjon relates to a phm mdulator and pafiicularsnfy RF source 10 may be connc~ted to eainer ports 1ZX or S2d 
to a phae mdUBatoP utij&ang tuned va~abBe len@h electrBcaj 5 and lad 11 connected lo the other p a t ,  I :: gorPi >2A i W  
lnnes B2B may be rnterchanged wrth successful operili-csu 
Phase ivodulzikom are used In many FM transmntters and Coupbed2 can be of any mncnossrW En wher:lr be 
recenvers Generally, the hlgher the frequency at which such a  couple"^ a quarter-waveiengbh of I J ' ~ O  WuencY 
modulator aaprate, the smller the of componentb are signal Such couplers are well knowl mtd wsik not i:e fuflPecr 
Lapi;lzxd such compxmess is hig$lly desired in eiecrronic ap- described for that reason In the illustratrv:: emboi5nn en? I *  - 
paratus. ne phw modulator should have a large isnear phase desired that a 3DB qudner-waveiengrh cauzker be used r 
shnft, such as up to a b u t  a radian peak mo8ulation. At lower cQnnection thetwotuned hnes li4md 
frequencies, of course, the modulatron rndex can be smaller Lines 14 and 15 have an electracal length detern r-ed an rcii? 
Therekbre, at the hagher frequencies of phase modulation, Q 1s , by the varactors 20,2B and inductor 24 fo- hne 15, and v a ~ i r i -  
a nn that d l  of the ComponenB must be carefully tom 22 and 23 and inductur 25 for lam 14 The ejectrlc~' 
selected and cmefully %embled to ensure that Q is main- length of lines 14 and BS as also affected by the phy\1ca/ Ieng~h 
ran& for egmhng linear phase Insenion losses of the structure (not shown) supposing rhc vdgik6tOi mad srq 
must be kept to a ~ n i m u m  in all instances. ductor elements as is well-known rn the art The 4F ene-fy 
20 reflected to ports 12C and 12D has a phase detetrnr.;ea by ..P- 
OF THE I N V E m O N  electrical length of lines 14 and rnad~~zi$~nc. .h& 
Ee is an object of this invenhon to provide a low loss phase 
mde~!ator of improved design. 
.4 feature ofthe invention is the connection of two electrical 
lines having an indudive element and a varactor diode which 
linearize phase mdulation through use of reflected energy to 
a qumer-wave coupler. 
A quafler-wavelenagh four PI% coupler connects an RF 
source e6, a load respctively &rough input and output ports. 
The two other ports of the coupler are refemed to as quadra- 
ture ports, meming that the signals thereat received from the 
input port have a 9P phase relationship. A pair of tuned lines 
are respec~vely connected to the quadrature ports. A source 
of modulahon signals elect~cdly varies the electrical length of 
the lines such that the energy reflected from the lines into the 
qudrature prts for tmsmission to the load v a ~ e s  in phase in 
accordance with the electrical tine len@h varialion. The elec- 
trical line reaamce is formed by capacitos and inductors. In 
one emwiment ,  the capacitors consist of varactor diodes 
which are reverse biased and have their reverse bias modu- 
lated by the mdulation source to thereby vary the 
capacitmce *and hence the electrical length of the line. The in- 
ductors are selected to compenmte for the nonlinearities in- 
troduced into the p b  middabon because of the nonlinear 
phase electrical line length relahonship as well as the non- 
linear capacihannce reverse bias voltage relationship of the 
varaictor dides. Inductors are preferably made variable such 
that the lines can be tuned to form a linear modulator. The 
v x z t o r  diodes are connected such %hat all diodes are in 
padie$ circuit relalionship with respect to the modulation 
source such that all capacimces of the various diodes vary 
simuEbneousEy in an identicd manner. The diodes are 
preferably clmely makhed and have a gmd Q. 
The akmhed HGUW shows in diagrammaP;;c form an illus- 
trative embdiment of the present invention. 
DETAILED D E E R B m O N  OF THE ILLUSTIRATIVE 
EMBODIMENT 
Refersing to the drawing, a source 10 of radio frequency 
signals supplies RF enegy to load 18 through coupler 12 
wherein the W signal is modulated by modula~on source 13 
supplied silgads. The RF signals are supplied to input port l2A 
and thence .axe $Hmnasmitted to a set of lines 114 and 15 wherein 
the electrical iiine length is varied as will be explained. 
Reflected energy is supplied through pa- 12C and 12D 
whnch then is coupld to ougksut port 12B to supply load 11 a 
p h m - m d u l a t d  signal. The arrangement is such that the 
reflected energy suppiid firou@ ports B2C and 12D are in 
phase at output p a  12B and out-of phase at input port 12A. 
In zwr&nce therewith, the s i ~ d s  are cancelled at input 
p r t  12A, thereby supplying no reflected energy to source 110. 
" '. 
capacitance ofthe varactors sn these lanss the -le~tr,:;nt lenigth 
of the lines are modulated, therefore, toe phase of the RF 
signal is phase-mdulated 
The var~ation of electrrcal line lzngr rs by imcauEde e7r 
signals on line 26 supplled fmnl wurce 13 thrcugh DC sdac- 
ing capacitor 27. The four varactor dndes KO, 21, 22 and 23 
are in parallel c~rcuat relatntionsh~p between ~r;acd~~:atin7 qorfrc I 
line 26 and ground reference potential Tilt mod~~Bd:io? it 
capacitance of all the varactor dsodes ns tIae same Tbe vdrdc- 
tor diodes are reverse blased by Hswpply connected t7~trplgg!i 
voltage dlv~ders 28 and 29 to msdu'ataon wurce Else 26 $11 ?L- 
cordance therewlth the electrical llrrc length of Elries 14 an d 15 
is symmetrically Atered by mdulatiow so7brcr 113 <ag~als 
L~nes 14 and 15 present an electrncdl line Eengh to pant 
12C and B2D whsch length as modulated by the va natzosa of 
capacitance of the varactor daodes 20 and 21 by eh. rroc3f~- 
rion source signals. The electnsm! line Ees.ay1? causes r ch.~-gc 
rn phase of the PF sagnal auppraed tilereto bs Ir ~ v r * ! ,  k.rakr? xq 
the art. The reflected slgnals are phhe n;at>duld$e~ anc; 4s . i . i e ~ ~ -  
pled to input pea 12A are out-of-phase when ihc rmpcdwcei 
of the lines 114 and 115 are equal That as, the refiececd eneigq 
at port 128 1s 180" out-ofphase wath respect to the eneag 
suppiled to input port 121% from port li2C Uov~ewi:  because 
of the coupler action, the reflected energy at north 126: aqd 
12D are Bn phase at output port B2B. However, if the cle,ir,ca 
impedances of lines 14 and 15 are somewhat ~ I ? u ( ~ u ~ P ,  :PI\ 
phase relatronshnp is altered such that the p b a s  re ationshnp h r  
~npuh port 12A is not 180" Snmalarly, there 1.; siyht  out-4- 
phase relatlonshlp at output port BPB Thns ~ R E I c ~  CA~SCP. bee 
relationshnp causes diston?non an the phase mouu)ato: wave 
and reduces the power throughout Therefc%re, *P -9 quite ~ m -  
portant that the electrid impedances of arnrs 14 araci 15 b2 
made equal Accordingly, for optimum I w a s  aperapon, thL 
varactor diodes 20,2B, 22 and 23 should be c;d~ef~~lFy matchx 
as to their voltage capacikance character~strcs 
It is well known that tihe varlatson of capacttsxx w el? 
respect to the vanation of reverse bias vai,ag., ~ C T ~ ? S B  the 
varactor d ~ d e  1s nonlnnear Further. B B  BS knov+"i tCIr& !he p i l w  
variation of a signal caused by a va~atron In -1ectncai &eng?ir 
of a line 1s a tangential funct~on That ns, 11 as quate nonls~e  21
To linearize the phase modulation of tb- present modulafo~ 
inductors 24 and 25, both vanable, are c2-i-rccted iv *enes c,s 
cuit relationsllip to electrical Innes 14 and 15 I F  one CCPS 
structed embdment  operating at a 5630 megahei-t-. racl~ 
signal frequency, inductors 24 and 25 -ere m~cr.sstyr;, Irres 
The length thereof was adjusted an accordasce w t h  Sinosvr 
microsdrap techniques At lower frequen~cte.a the nnductmcer 
24 and 25 may be lumped components, sur:!;! as a sldg tua:d 
inductor. It 1s known that the inductave ~ r ~ p a n n c e  vanes on- 
versely wrth respect to varhatnon of capacrpve lin*,~edance Ir- 
ductors 2A and 25 are carefully seiected r9?, to eongen- 
sate for the voltage versus capacnhnce cl?a~acfe-sst~c\ of t5e 
diodes in the respectwe lines as well as the t, ngent dl varyatnor 
3,579,147 
3 4 
ol- phase with iespect io 3 vanation of eiecirizzi line length. By radians as afunction o fa  series ~nduceancc L 1s. 
so carefuily selecting inductor; 24 and 25 and adjusting them 
after assembly. a linear phase inoduiator is provided. R o 8 -  2 - - I  -. .-. - -- 
Radio frequency chckcs 35 a i d  36 are added to RF isolate OJi-- IT7/,.'. >: <5 j 
lines 14 and 13 respeciiveiy from the bias source and the 5 
modulallcjn qouTce 13. .rhe radio frequency chokes 37 and 38 wherein Ro is the hybrid characteristic ~mpecla~~cu, pi IS :hi. 
arc provided complete a between the & voltage across the diode o is the frequency in radi:iili; ard M 
ft>r reb.erse biasing ?he dic;des 20 and 22. These chokes, by ;Re varactor reactance (center, i.e., for nc rnodti'ation). '%6 
proiiiuinq a DC rer;~m to ground, prevent the DC: from af first derivative of 0 with respect no voltage i:? radiarls Tser .vo!- 
f eiting : opcrallon of ?,>lircc 10 aild load I I via coupier 12. lc is: 
Diodes 28 2nd Z2 in addition :r, providing a variable (LIB %Ro7'Vr-i . - - -- -- d 17 -- capacitance lo lines 14 atrd 15, serve as blocking capacitors to 
isolate the DC source from dividers 28 and 29 from supplying 
DC current to W' source 110 and RF load 1 1. Diodes 20 and 22 
could be rt:piaced by fixed DC blocking capacitors. Aitema- 15 From the above equations a phase :nociuhioi :sn i.;i 
lively. diodes 20 and 22 could be eliminated with fixed designed using known microstrip teehsiquec. 
blocking capacitors being connected ai RF source 10 and load At half-radian peak variation in phase :hew is n r i g  ?XO":L)' 
11 :errnirals. In this lattcr alternative connection, W chokes minus i percent error in the illustrated modulator in L ~ C -  
37 and 38 ma) bi: disperwd with. Alternatively, diodes 20 and cordance therewith cascading two nr nrore ni these phasab 
22 may be left in with diodes 21 and 23 being replaced by modulators can result in improved iineiiriq at th.2 experirc of 
f xed i.ap;zcitoi-s. additional circuits. For exampie, a 0.5 radizn peak ~i"".tii3.:? i? 
'K'hc r p-;.ation orthe coupler 12 with respect to iincs 64 and phase only a 0.6 percent disfortior :ern lae ct-tair.,ee 3q 
15 acts as a four pork device where an incoming signal at port cascading two identical phase modulators ofthis ii~vciltlon. 
1213 Is divided into t~vo ewtputs at ports IZC and 12D which Another characteristic of the i'liustratcd pl~ase mc:dulseor i s  
are in ph:%e qi.ladrature (91)" out-of-phase) al:d are JDB below th;rl there is amplitude modulation present ctn the atitput for i 
ihi: inpir'c p:?wer !eve] ?or a 3DB ceitpler. A ~ p i c a l  insertion constant voltage modul;ating signal. Such ;m]7!iti;ii;e ~ariatioa: 
loss is about c.5 db. with the two quadrature outputs at B2C arise? if the <jio& QIP vary over the dyr:am:c rai.ge of t)sc 
;md E2D being balanced within 0.5 db. Output port 628 is This can b: a problem [hecause p.esz.?r 
connected to ?oad 11 which has a icsistive impedance which 311 varacecrs do nor have a sufficiently high 0 at. 509 imcgel.~e~';~. 
should be eqcai to tlre hybrid characteristic impedance and with the varying Q soniewhat with reverse .,::;~l~;~:. i13crcfL>';lre 
v ~ I E  r.?ceive no pou,er urliess h e s  3.4 and 15 have a VSWR ;t is important to have very high () v:;racri;r dii.dei. 
o.r%cr t?an i?ne. Is\Izticn belweerI input port 1211; and output We claim: 
pokq 1 XZB of 30 to 50 db. is achievable. 1. A phase modulator, including in comb;r:aron: 
When lines 14 and 15 have equal Lmpcdanccs, the input 35 a coupler having input, c?utput and n p l r -  :?h-:~.a3rai.~re 
VSW? port 1114 ~elaazr~s Low. If &!IS lines 14 and 15 api?ear p m s .  
i;l.?omtl, ihe RF pjwer rirfzcted at port 12C di4des between firs: and secor:d tra;..snrission lines respzcriveiy ::?nneci::e 
poCs 82A and i23  "*;-.;I- rcfiect~xi power frnrn part 32D dm to said quadrature ports, said transrpiiss:on iilr.rs fach ha.!- 
divides eynially beiuzir~ pogis 12% and & l A i  !-iowever. it can ing an Ernpdursce rneans inciilding se-i-r; co~r:?ct~d :.-,I+- 
be shown rnat.h-t-t,;~t~:'.i~I> which i s  beyand the nece"""Q1 ii.0 of the cavaci:ibc a;ld jrlglicliVZ- 
r.aca.?.g fcp. t h ~ s  ~nvmtion, that the reflected power corn.. 
'.-- . - " ' C  tYP" 
t i i i ! r ;  ar2 O U I - O ~ - P E ~ J ? ; ~  at the ir1put port 1% but are in . . modulation means connected rcb 5186 :..p sci.ii~c rtactailcil 
p h a c  at outpat port 12B. instead of shorting the lines 14 and means for eiectricdlji varying same fc,; ijlte-i:~~; the  tic-:- 
15, the ! i x s  ar,: terninnatel; in the variable reactances 
. " ,  . 
crical 1engtI-i of said lireeh. said lines being syqrimetricaitr' 
pr.;s.;,tr: " y:!e var,.,::c,r d;oaeb a;id & v ~  <,!Lir:aaar in.. 4-j cnisposed with respect to said i ~ ~ u l a i i o c  source ~dc i l i  :bar 
dkcianzes. Since p; wi.:. is &so:Sr,: in a pbre rearane-.,, the electricai Feagt"raf btreh iines varies i3c:iticaIiv. and 
iilost of thc input power is reflected to be supplied t11rougi-1 the impedance means of said lines being matched as Ic' tnci: 
output port 'ZB thence to Ra" Eoad i I .  The phase relationship respective impedances and vioiatioo of ~cac.;lve ir:- 
betuee:: the ;igm;si i:t l : ~ p ' i :  121% a n d  Cht cutput port 828 pedances with respect to said signais Crorr? sEd "?3ci::iz is d;-per!dezl cri me ,jri A; S Z ~ - , , I ~  . . L G r . ~ ~  ;resented i.: lines I4 and 50 iron sotirce. 1:s. 
Tile reflection coefficient in tcrms of terminating im- 
pedance is a tangentid function of the variation of electrical 
length of lines 14 and 15. Ef B is the: rrf:ectiozm angle, i.c., the 
phase si:iR, Z,, :k: char~.ctci.iscl; imped;mce and Z, the ter- 
minating irnpedailce an; angle 0 is: 
@==2tannZ,i&. ( 8 )  
Onc known formula f ~ r  varactor diode capacitance versus 
voltage characteristics is: C=.#8/' -? ( 2 )  
<;hertic 7 ,it be'cu,.:t:n oce third aimd one half deperading upon 
the hnanufacturing process of the particuiar diode, ie. .  the 
junction characteristics; C is the capacitance: K i s  a conslant 
and V is the reverse voltage. 
To determine the value of the inductors 24 and 25 for 
linearizing p"r, modulation operations; one must take the 
first derivative of 0 with respect ?o voltage to detemine the 
percentage nonlinearity of any desired phase modulation 
operation. Bnductons can be either a series inductance or shunt 
inductance for linearization. The illustrated embodiment uses 
a series inductor. Tests have shown that a series inductance 
works much better than a shunt inductance En lineawzation of 
the illustrated mdulator.  This is desirable even though a 
shorted transmission line can be used to make a good shunt in- 
ductance 
Accordlnely, dcugn crlterrd for a senes xnduceor only 1s 
gaven laerc~n WI* respect to the phase rnoaularnon sndex 8 in 
2 A phase modulator ~ncludrns the co-niirva iLr 
a quarter wave coupler havrng rnpsnt anu cil*pi~, r, xrk ;l 
pair of quadrature ports fop recerclqg rrPcctec er ere< e 
be supplred to saad outpot port?, 
firs1 asad second transmnssson iianec resp cePve, : nrccf 
to s a d  quadrature ports, s a d  trans-nrssko? 1 nec \bet- 
ldentlcally constructed and each in i iudl~a f ,  iswr >e e 
snducror and capacvtor eleirrent for ier.nlr,aI,rg $3 LI: 6u 
a mduiaklon sagnal source conne~;Bed to b,iii- .;ad :, ;ci LC- 
cornplet~ng a pair of pardie1 clrcults seV/Je?- ,, ,> \e ,. 
~,)nnected znductor cicnlerits and e,i,,ac *or c c t,-a:-, 
czch saad llne for applying h a s  voltdg* there, cro*i a , c 
cordance with mdula~hraon sngnds, mzii ~ d p d - ~ i a i  ~12: P* i 
being responsive to modulataon slgnzls 'or v c ,  ---,o r 3 %  
capacrtive reactance thereof for thereby vdrj ng )he 
fectlve electrical length of both s a d  iines ~ d e ~ t  c ~ ' I j  t i -  
fect phase modulat~on of the SEpSI3La 91:rag *I PFILC, 
through s a d  coupler 
3 The subject matter of clarm 2 f ~ r t h e r  mclua n, : 11-0 3 -, 
fourth capacltrve reactance elements intcr powd 1-e \i;rcq , r ,  
, " ' ' "lep'lc US$ quadrature ports and s a d  serres coalnecreC Lay7&r i a  . 
and rmductor elenre~~ts and bcled to be retlrs\: P ?-\el idti, 
modulatnon sngnais 
4 -1%~ subject matter o l  ciaam 3 whcrt sn %?I\: c~~sa,. t 
rcacttve elements are connected an ~ornrli in :> <,*id ~ i o t  wl; 
tlon sngnal points thmugh radlri freu ~ C P ;  rho p\ 


Phase modulator Patent

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