IEEE TRANSACTIONS ON MICROWAVE THEORY ANDTECHNIQUES,MTT-34, NO, 12, DECEMBER 1986

VOL.

A Compact 4-GHz Linearize
RYUICHI

Abstract
TWTA’S—Acompact
is composeda limiting

ampfifier,packages,

respectively.

of a preamplifier,of two,It improvesby 3 dB and the required

C/Nsatellite

aging test were successfully

OGAWA,

fhtearizer

packages

SUSUMUfor Space Use

KITAZUME,

satellite

TWT 1TWTA.

and25X 12.5-mm
COUPLERsystem by 4.5 dB compared

A space environmental

GOW%ERGtest and anon the equipment.

INTRODUCTION

INPUT

cationsystemsfor

their

large

weightandpowerconsumption.

outputwill

significantlyperformance.
methodambiguities

affect the satelliteThe

forlinearizing

for

In

satellite

reducing

signals

communication

techniquethis degradation

isTWT 2

DELAY
(a)

power

in transmitting

a~v
FREDISTDRTICN TWT
LINEARIZE

andsystemaneffectiveof the TWTA

COUPLERI

communi-transponders,
it is desirable that the TWTA
be operated
near saturationlevel. However, the amplitude
and phase
distortion
degrade TWT performances,
as seen, for example, in AM/AM
conversion
and AM/PM
conversion.
These degradedparameterswill cause intermodulationand phase

DELAY

the noise power ratio for an FM systemused in satellite

noise

AND P. DESANTIS

chip devices.
Iinearizer,

and three

WT’S are most commonly

reasonableforwitha predistortion
three,

for a TDMA

performed

I.

T

4-GHz

by using MIC

consistingwith the conventional

HIROSHIand lightweight

has been developed

The linearize

INADA,

:1327

(b)
Fig.

1.

Block

diagramofthe(a) feedforward
methods.

and(b)

predistortion

re-sponse.
Thispaperformancedescribes

of a linearize

the design, construction,
for satellite

and per-TWT’S operatingbothin SCPC and in TDMA
modes. Space qualification
tests
includingaccelerated
aging tests were successfully
performed on the equipment
and the results are summarized
in Section

pensatedsignal. This method

closedHowever,loops.

passivelightweight,
II.

LINEARIZE

There are several methods
earity;ofthese,DESIGN

to compensate

feedforw~d[1],TWTA[2] andnonlin-that of TWT1.
The two signals
error-summing
coupler. The error
TWT2,

and the output

signalare comparedinsignal is amplifiedof TWT1

is delayedby atime equal to TWT2.

The two signals are then combined

ancoupler

error-injection

whoseoutput

isthedevices.

incom-Marmscript
received April 3, 1986; retised July 1, 1986. This work wassupported
in part by INTELSAT.
Any views expressed are not necessarily those of INTELSAT.
R. Inada, H. Ogawa, and S. Kitazume
are with the NEC Corporation,
Yokohama,
Japan.
P. DeSantis is with INTELSAT,
Washington,DC.
/IEEE Log Number 8610835.

andnotwocanbecompact,

predistortion

typewas selected

fordiagramof the 4-GHz

linearize.

thetransponders.

consists

itFor thesesatelliteItThus,

consumption.

Fig. 2 shows the block

thebyTWT’S

and have low power

reasons,predistortion[3]-[11] are widely used.
Fig. 1 shows the block diagram of the feedforward
andpredistortion
techniques. In the feedforward
method, theinput signal is divided into two paths: one for TWT1 andthe other for a reference path whose delay time is equal totwo

delay lines, which will increase the overall weight andpower consumption.
On the other hand, the predistortion
circuitcan be realized with low-power
amplifiers
andseveralIV.

is stable, since it contains

it requiresof 3 sections:a preamplifier,

usc ina predistortion

linearize,
and a limiting
amplifier.
In the preamplifier
section, the input signal is amplified
to the level required
to drive the predistortion
linearize.
Amplitude
and phlase
distortionis generated in the predistortion
linearize
sectionin

pensateamplifieration,

accordancewiththe input

the nonlinearity
section preventsand constantthe saturation

input

the limiting

amplifieroutput

power

level

to com-can be obtainedlevel. The predistortionand it can considerably[3].
Construction

powerof the TWTA.
The limiting
the TWTA from overdrive oper-is called
improvelinearize

abovewitha soft-limit-typelinearize,

the bit error

rate (BER)of the predistortion

linearize

sectionisshown in Fig. 2. The input signal is divided into two paths:
one is the linear route and the other is the distortion
route.
The signal in the linear path passes through the phase0018-9480/86/1200-1327$01.00

01986

IEEE

IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES, VOL. MTT-34, NO. 12, DECEMBER 19861328

PRE

PREDISTORTION LINEARIZE

AMPLIFIER1IIr -------= --LIMITINGAMPLIFIER

I

1iwi:: g;r ---.

I

Ly’JErdgr-------------;? HI

lr--------l!

IIII
1- -------.

..-,!
IiI

IJISTURII! UN--, ,7=J------

H.-----Fig.

2.

““”

ATT

8.

Block diagram

iof the 4-GHz

l___=L_J

J---------

linearize.

o-. 120- 11.5GAIN

10 -.—

Gs%~/~- 10.5\~NpuT\- 10.0 sg/’-.—I—.\.
OUTPUT
RETURN LOSS

30 -—-1.

?

\RETuRN LOSS

20z
E2&,*;,\\,- 11,09.0=,.
\.
~._+&lP,o~

3.5

3.3(b)

3.7

3.9

4,1

43

4.5

4.7

FREQUENCY (GHz)

Fig.

3.

Vectordiagram of the predistortion
linearize
nal level and (b) higher signal level.

for (a) small-sig-Fig.

4.

Gain

and returnloss of the balanced-typeamplifier,5-shifter

and the amplifier,path passes throughand the signal in the distortion

the amplifier

The signals are combined

and the p-i-nby a hybrid.

attenuator.

of the predistortion
linearize
is shown in Fig. 3. Vectors Aand B show the gain of the linear route and the distortion
route, respectively. Vector C, which is the vector sum of Aand B, is the gain of the output signal. A phase difference
betweenthe two vectors of about 180° is required
toobtain

the desired predistortion.

For small-signal

level, thegain of the linear

route and that of the distortion

route areconstant.

the gain of C is constantThus,

4-SATURATION

The vector diagram
32-

SMALL SIGNAL

1,n3,85,7

3.9

4,04,14,2

and no phase

distortionis generated, as shown in Fig. 3(a). When theinput power increases to a higher level, the input level ofthe amplifierof the distortion route approaches the saturation input level; hence, the gain of the distortion
route isdecreased. On the other hand, the linear route is still at thesmall-signallevel; hence, the linear route gain is constant.
Therefore,
the gain of C is changed to C’, and the phase
distortionrp is generated, as shown in Fig. 2(b). The angle
f3 between A and B can be adjusted by the phase shifter,
and the gain of B can be adjusted by the p-i-n attenuator.
Therefore,
the linearize
can be adjusted for various typesof TWTA’S.
The linearize
consists of eight MIC packages, as shownby the dotted line in Fig. 2. The first two packages form
the preamplifier.
The predistortion
linearize
is composed

FREQUENCYFig.

5.

@AZ

Gain and gain variationof the linearize.

of three packages that follow. The last three packages are
the limiting
amplifier.
The size of each package is 25x 12.5 mm, wtich
includes MIC’S of 0.381-mm alumina substrate and several
chip devices such as GaAs FET’s, p-i-n diodes, and varactor diodes. The metal caps are laser welded.

Balanced-typeamplifiers,
p-i-n attenuators,
and a phase shifter are used
to provide wide-band
performancesfrom 3.3 GHz to 4.7
GHz, Fig. 4 shows the typical gain and return loss data of
thebalanced-typeamplifier.
Theisolators
can beeliminated,
and a compact and lightweightlinearize
isrealized.

et a[. : 4-GHzLINEARIZE

FOR SPACE USE

Frequency

3950 MHz,.
0/+50 ~
TWTA+40 t>–--e--c-..
73+30s= +20

1329-0-..

—O-$=

10c1CENTER FREQ. 3950 MHz—Power‘“;~‘----phase././%’’’.O.,,

TWTA/Linearized#P”/,;

20 -25+100*;_+._”’’’..,
Linearized TWTAa*..-+-’>,.’ ,“

T30, j /’10’J,.,

o—o Af

5 MHz%,//–20

35

2015Input

6.

x~A‘~~:---..:;[$<.

Fig.

&J%:#/’

15 -#Input/output

10Backoff

5(dB)

0–340

power and phase transfer characteristics
TWTA and the linearized TWTA.

of theA—Adf 5Mffz❑ -O Af 20 MHzx-x

Af 50 MHz45

5--1oOUTPUT

20 Fig.

8.

Third-order

BACKOFF(dB)

intermodulationof the TWTA
TWTA.

10 -andthe linearized0 –~ .,0:

5%
$-20

10 -

Frequencytslot

1248kHz/:5~’Aa-30-40-50-TWTA
g 20 --IIII

15

1050INPUT

7.

,/’

1/-Linearized.~

Input/output

power

and phaselinearize.

BACKOFFtransfer

TWTA./

30-1 J7“/025–#‘3.2dB/“’

IFig.

/./:/

15 -\1./(dB)

characteristics

35 /./
1of thedo~

10Output

The Iinearizer contains the RF section, a voltage regulator, and bias circuits in one housing. In the RF section,
the MICpackagesusing Teflon

length,by microstrip

glass substrates. The shielding

to get adequate
amplifier.

are connectedisolation

The dimensions
110 mm in width,

between input

Fig.

9.

walls are madeand outputof the linearizeof each10-4

Uplinkthe weightPERFORMANCE OF LINEARIZE
LINEARIZED TWTA

The linearize

is adjustablebias voltage

and current

attenuatorsin order to compensateof the phase shiftertheand the p-i-nfor the nonlinearity

10-7ofthe TWTA. The TWTA used in the experiment is a Hughesmodel 249H, which is the same as the on-board type TWTINTELSAT-V.

pensatedThelinearize

over the range fromsensistors in the bias circuits
the phase shifter.

10”Cis temperatureattenuators

andTWTA \.\“ 1.

----i10-0 ~14com-to 40°C by using theof the p-i-n

O~O<WTA\Linearized

1o-6

controlling

C/N=18dB‘\*=%o_oKumAND

by externallyTWTA\\

10-5

III.

and the linearized:\.

are 160 mm inand 23 mm in height;of the TWTAo(dB)

10-3 rline circuit

is 461 g.

forNPRB~ckoff

Fig.

10.

16

18 20 22 24 26
Downlink C/N [d8}BER of the TWTA

28

and the linearized

30

TWTA.

The gain and gain variation at small signal and saturation are shown in Fig. 5. The gain variationof the linearize is less than 1 dB p-p from 3.7 GHz to 4.2 GHz.
The input/output
power and phase transfer characteris-saturation
output power of the TWTA,
and O-dB input
backoff corresponds
to the saturation input power of theTWTA
and linearizedTWTA.
The power transfer characteristicof the linearized TWTA
is almost linear up totics of the TWTA and the linearized TWTA are shown inFig. 6. An output backoff of O dB corresponds
to thesaturation,and constanttransfercharacteristicofabove saturation.
The phasethe linearizedTWTA
is sup-1330

IEEE TRANSACTIONS ON MICROWAvE THEoRY AND Techniques,F1=3947,5MHZ

10Reference

Performance

voL. MTT-34, NO. 12, DECEMBER 1986

Testx

F2=3952.5MHz

A1/[[ThermalCycling

Five cycles
overtemp.
range

survivsi!

Power

Aging

168

hours

at 40”CI

InitialPerformance

Test[IThreeAxis

Vibrationa.

Sinsoidalb.

Random.50 ~10Fig.

Thermala.

VacuumTen12

Third-order‘OFF”

oversurvival

temp.

range

A—A10C.—.

2YC

140C

TestanIFig.

pressedreduced

1 monthI
FinalPerformance111.

linearize

Test flow of the qualification

conversion
input/output

The

gainofthe linearize

The phase variation
versus the input power is about 40°
opposite to the phase variationof the TWTA.
Thus, thephase characteristicof the linearized TWTA is reduced, as
shown in Fig. 8, compared with the linearize.
The third-orderintermodulationof the TWTA and linearized TWTA are shown in Fig. 8. The center frequency is3950 MHz, and separation frequencies of 5 MHz, 20 MHz,and 50 MHz are used. The amount of improvement
due tolinearization
is 23 dB at 4-dB output backoff.
The noise power ratio (NPR) responses are shown inFig. 9. The linearized
TWTAimproves 11.6 dB at 7-dBbackoff.

Alternatively,

the effective

creased more than 3 dB compared
the TWTA
7-dB output backoff.

#/’/’

10withpoweris in-the same NPRofFig.

13.

off.

An NECBackoff(dB)

NPR data at thermal

Fig. 10 shows downlink
and the linearized05
Outputexpands as the input power increases. The output power islimited since the linearize
has a limiting amplifier
section.

outputx.%’

40 ~

is

input
power of the saturationof the linearized
An output backoff of O dB corresponds
to theoutput.

*/

tests.

to less than 50 p-p. The AM/PM
to 0.5 O/dB from 3.0 °/dB.
The

saturation

test

Test

power and phase transfer characteristicsof the linearize
are shown in Fig. 7. An input backoff of O dB corresponds
to theTWTA.

20z

vacuum

Il,700KHzt
10x—..

forslot

515

Test

data at thermal

Frequency

tAging(dB)[b.
Ten cycles‘ON”
over temperature
range
from IO”C to 40”C.
Test at four temperaturesuch as 23 “C, 10 “C,In addition,
maaauredat O “C40”Cand 23”c.
and 50°C for reference
only.

Performance

Backoff

intermodulationoTest

cycles05Output

TWTA

120-Mbit/s

C/N

vacuumtest

versus BER of the TWTA

operating
QPSKat O-dB output

modem

back-was used in theexperiment.
The values C/N = 25 dB and BER = 7 x 10 – G
were chosen as a reference. The resulting downlink
CNRof the linearized TWTA is 4.5 dB less than that of TWTA
to achieve the identical
BER at downlink
C/N=25 dB.
Alternatively,
the effective power can be increased by 4.5dB.
IV.
Qualification

SPACE QUALIFICATION
tests

forthe linearize

TESTS
wereperformed

accordingto the test flow shown in Fig. 11. Before thequalification
test, thermal cycling (from – 40°C to 75°C,
five cycles) and power aging (168 h at 40°C) were performed.
The linearize
tion,

randomwas subjectedvibration

to sinusoidal

tests, and thermal

sweep vibra-vacuum

tests atet al.: 4-GHz LINEARIZER FOR SPACE USE

INADA

1331,~-z

NOISE
BIT

ERROR

CARRIER[ \RATEFREQUENCY=3950

RATIO

MHZ

“\*\,.-3POWER

NPR

40,~-4uwm

A—AIo”c“–*—X

23-C

*...

_____

CL.-.-.------3

10,~-5●I

7_ DAB________ ~.. __-___x. --–-*____*.

5DB

20 t4o”c—————

9DB

I*30d1°

E 6-.---C--

U---------Q----D

0oBO: IDB

Ot-;

10100

1610
TIME

Frequency,.-6Fig.

16.

Trend

slot

data of NPR(H)

1248kHzof linearizedTWTA.

BIT ERROR RATE
BER
to-z,0-3

10121416-

1824

2220

14.

,0-4

BER data at thermal

vacuum

test.
10-5

TWO
lM

TONE

1°

C/Nt: IODB
‘1m --------------

C/Nt
Fig.

-1

INTERMODULATION

(DB]

10-6

I

o---.

-x

*--------.~---_._.x-~---

10-7

L
140aA

IA

160S

x-----a----14DB~_-_____ -_. _-----x-50 ,-Q___

12DB- __ -.*--.--*

II

10100

--- -x
1TIME

4DB
OUTPUT
30-20m------3~;-------.

-s------------

e----aFig.

: 2DB

environmental
The linearize

FI=3947.5MHZ
10F2=3952.5MHz
110o;

Fig.

15.

Trend

the vibration
satellites.

75 ‘C),

intermodulationlevels and temperatures

was performed;
performed

1100

data of third-order

During

Trend

:

ODB

data of BER of linearized

TWTA.

o0OBO

17.

BACKOFF

liloo(H)thermalvacuum

ten cycles withover the survival

1000
TIME (H)of linearized

TWTA

experienced

in actualtests, thermal

cycling

power

temperatureturnedoffwererange (– 40°C toalong with ten cycles with power turned

on over thetests, thermal vacuum tests, and aging tests.
improves
the third-order
IM, NPR, andBER of a TWTA.
It has been shown that the effective
power can be increased by as much as 4.5 dB for SCPC
and TDMA
systems. The linearize
is adjustable for various types of TWT’S.

ACKNOWLEDG~NTTheauthors

Betaharon

wish

toof INTELSAT

encouragement.

thankDr.

P. Nuspl

and Dr.

for their useful discussions

The authors

also thankK.
andDr. T. Muratani

temperature
range from 10°C to 40”C. The test results ofthe linearize
in the thermal vacuum test (TVT) are presented in Figs. 12–14.
The aging test was continued for 720 h at 40°C in room.

and G. Satoh of KDD

This condition[1]

D. Chakraborty,[2]transmission
through bandlimited
satellite channels,”IEEE Trans.
Commun., vol. COM-25, pp. 1233-1237,
Oct. 1977.
M. Sidel, “A microwave feed-forwardexperiment,”
Bell S)Jst. Tech.

performance
Trendlinearize

is equivalent
was measured

to 4320 h at 23°C.

Electricalwhichshow that theis stable with time.
[3]
[4]
V.

CONCLUSIONS

A compact, lightweight,
and stable linearize
for satellite
applications
has been developed using MIC packages. It
has been shown that the linearize
is stable throughout
thediscussions.

ILf3FEWNCES

at 24 h, 96 h, 288 h, and 720 h.

data are shown in Figs. 15-17,

for their technical

[5]
[6]

“Considerationof a 8-phase CPSK-TDMA

signalJ., vol. 50, pp. 2879-2961,
Sept. 1971.
G. Satoh, “ MIC linearize
for satellite communications,”Tram.
I,EC.E, vol. 67-B, no. 6, June 1984.
Cr. Satoh, “Linearizefor high-power
traveling
wave tube amplifier;’ Tram. IECE, vol. 62-B, no. 10, Oct. 1979.
CT. Satoh et al., “A linearize
for satellite communications,”in Int.
Conf. Commun. Conf. Rec. (Seattle, WA), June 8-12, 1980.
L. F. Gray et al., “Applicationsof broadbandlinearizes
to satellite
earth stations, “ in Int. Conf. Commun. Rec. (Seattle, WA), June
8–12, 1980.

1332

[7]

[8]

[9]

[10]

[11]

IEEE TRANSACTIOI’JS ON tvUcROWAvE THEoRY AND TEcHNIQu%Hiroshi

G. Satoh and T. Mizuno, “Nonlinearsatellite communication,”
inSth Int. Conf. Digital Satellite Communications(Genoa, Italy), Mar.
23–26, 1981, pp. 47–54.
M. Kumar,J. C. Whartenby,
and H. J. Wolkstein,“ Predistortion
linearize
using GaAs dual-gate MESFET
for TWTA
and SSPAIEEE
Trans. Microwave
Theoryused in satellite
transponders,”
Tech., vol. MIT-33,
pp. 1479-1488,
Dec. 1985.
A. Katz,
R. Sudarsarram,and D. Aubert,“A reflective
diodelinearize
for spacecraft
applications,”in IEEE
A4TT-S Syrnp.
Dig., 1985, pp. 661–664.
D. Cabana, J. R. Potukuchi,
R. G. Marshalek,and D. K. Paul,“Linearizedtransponder
technology
for satellite communications
Part I: Linearize
circuit development
and experimental
characteri-vOL. Mn-34,

Ogawa

was bornin Gunma,

Japan,

on

September9, 1947. He received the B.E. andM.E.
degrees fromthe Waseda
University,
Tokyo, Japan, in 1972 and 1974, respectively.
He joined the Space and Laser Communications Development
Divisionof the NEC Corporationin 1974. He has been engaged in the
research and developmentof microwave components and equipment
for communications
satellites.
Mr.

Ogawa

is a member

Instituteof Aeronautics
and Astronautics
and Communication
Engineers of Japan.

zation,”COMSA T Tech. Rev., vol. 15, no. 2A, pp. 277-308,
Fall1985.
Y. S. Lee, I. Brelkm, and A. Atia, “Linearizedtransponder . technol—..
ogy for satellite communications
Part 11: System slmulatlon~dperformanceassessment:
COMSA T Tech. Rev., vol. 15, no. 2A,
pp. 309-341,
Fall 1985.

ofand the InstitutetheAmericau

of Electronics

Susumu Kitazume
received the B.S. degree inelectrical engineeringfrom Tokyo Metropolitan
University,Tokyo, Japan, in 1960.
He joined NEC in 1960 and has been engagedin the research

TELSAT

Ryuichi Inada was born in 1958. He received theB.E. and M.E. degrees from Osaka University,
Osaka, Japan, in 1980 and 1982, respectively.
In 1982, he joined
the NEC
Corporation,
Yokohama,
Japan. He works in the Space Laser
Communication
Development
Division,and hasbeen engaged in the research and development
ofmicrowave equipment.
Mr. Inada is a member of the InstituteofElectronics
and Communication
EngineersofJapan.

NO. 12, DECEMBER 1986

VI,and developmentof microwave

communications
equipment,
especially
microwave devices. He is engaged in research anddevelopmentof the transponder
for the JapaneseCommunicationsSatellite-2 (CS-2), Commercial
Communications
Satellite(CS-3), AeronauticalMaritime
Engineering
Satellite ‘ (AMEX),
INand millimeter-wave
communications
equipment.

Mr. Kitazume
is a member of the American
Instituteof Aeronautics
and Astronautics
and of the Institute of Electronics
and Communication
Engineersof Japan. In 1971, he won the “Invention
EncouragementPrice” from the Society of Invention
for his investigationof the temperature-compensatedmultielement
waveguide device having susceptance elements. He also won the “ Ichimura Specird Prize” from the New Technology Development
Foundationforequipment
for satellites” in 1986.

P. Desautis,lication.

photographand biography

the“Development

unavailableofon-board

at the time of pub-