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INVITED PAPER
PHASED-ARRAY RADARS:PAST, ASTOUNDINGBREAKTHROUGHS ANDFUTURE
TRENDS
Phased-anmj radars Juwe seen ever increasingly wider use around
the wodd over the last five decades. Inrecent years, they have seen
breakthroughs that led to capabilities not possible in the past.
This isexemplified by the devehrpment ofGaAs integrated niicroivave
circuits called monolithic microwaveintegrated circuits (MMIC) that
make it pos.nble to build active electronically scanned arrays
(AESA) thathave lighter weight, smaller volume, higher reliability
and. lower cost. These developnwnts liave readied thepoint where it
is now possible to build a low-cosi 35 GHz phased airayfor a
missile seeker costing$30/element (total cost of array including
all electronics divided by the number of elements). This is
madepos.sible because integration allows the whole T/R module to be
put on a single chip. For some applications,it wiU soon be possible
to put multiple receivers or transmitters on a single chip. The
advances provided byMoore's Law have now made it feasible to do
digital beam forming with all its nmnerous advantages. Thisarticle
describes these advances and also covers the potential for GaN and
SiC chips that have thecapability of higher peak power by a factor
often than G
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Fig. 1 Example luhe (T) and salkl'ntate (SS)ssiff plitiscd
arrays having large
h
GRUNMMI e^DHAWKEYE
RAT31DL
APG-63
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COVER FEATURE: NOW
SHUTTLERADARTOTOGRAPHMISSION(SRTCISIR
/'Vg. .3 Other phused arraif siisivmHdeveloped or ttnder
development.
vd (see Figure 6).2 DARPA alsohindt 'd (lt'\('l(}pin('nl of;!
$10 X-l)aii[l, 10 iiiW. siiiule-cliip T/R niocl-ule.^ A 76 CM/,
photOL-tclifd Hdtnumlens arra)' costing only a few dollarsWHS
de\el()pe(l inr aiitoniotixi' cruise
l'
TABLE IBREAKTHROUGHS
Ffiased iirniy.s i'\
(SBX) nidur35 ( ; M / $19 K active pluiscd anny L()w-C(wl MKMS
])lia.sd
GaN.SiCSiGt', CMOS
Digila! bcaiiil'oriiiingk and iisscinlily
M!M
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45,056 Best-of Breed Tranimit/Receiver modulci
* 128 modules per lubarray(352 tubarrayi total)
Time-delay steering at thesubarray level tupportswideband
waveformi
* Nine luper-iubarrays - ctockodto tuppreif grating lobe
'> Xnii (iniiii (iirhUcrtiiri-.
Sure, we sell lots of microwaveand millimeter-wave
components.But, let's face it, sometimes you'renot looking for just
a component,you're looking to create an entiresystem. Come to us
for thecomplete solution. Give usa call and talk to one of
ourengineers. Together we'lldesign the system thatexactly meets
your needs.
ReceiversTransceivers/TransmittersSwitcii MatricesBlock
ConvertersRadar SubsystemsCoherent Converters i iCommunication
Systems ;Integrated Amplifiiar Ass
LOW-CO5T MEMS PHASED ARRAYIf only we had a low loss pliiLse
sliirter. Then we ooultl go
back to the passive-architecture electronically scannedphased
array with one mociule feeding many phase shifters(10, for
example). This could potentially reduce the eost ol'iUi
electronically scanned pluised array by a factor of aboutten.
Micro-electromechanical systems (MEMS) offer thispromise. MEMS
s\vitches have improved their reliability- bythree orders of
magnitiide over what was reported in Octo-ber 2003'' to a life of
6(X) billion switches.-^ -^ There is stillneed for improvement in
the loss. The loss through a fonr-bit phase shifter nsed in a 1-D
scanned radonie antenna^ ^ ^ ^ ^ space-fed lens (RADANT) is
-1.25
dB. Two lenses are needed for a 2-Dscan so tliat the two-way
loss for a 2-Dscanned RADANT array would be ~5clB. but proi^ress is
being made.*''
GaN AND SiC CHIPSWide bandgap GaN and SiC
MMIC chips offer the potential ofone to two orders inciease in
T/Rmodule power (see Figure 7).2"Table 2 summarizes the major
ad-vantages of GaN. Tables 3 and 4compare GaN with Gay\s. This
tech-nology would make it possible to up-grade an existing AESA by
replacingthe GaAs T/R modules with GaN orSiC T/R modules having ten
timesthe power. This provides either a tentimes improvement in
search volnme
Raytheon Buirt SI9KSeeker Array; -600 EL-$30/EL, -40mW/EL
l-'iii. 0 Su luw-cust \)fuised iiiratj-miltrue anymore.
10'to*
Ito*
Kiymofu
Twn
dubMBKT ;
SOUDIMTE
\
\
VACUUM
WOTRONJ
ElECTRONlAua
IMMTT
1 10 100FREQUENCY (GHiJ
A Fig. 7 Stute~()J-tlir-(in siiikl-ataic andtube devices.
36 Visit http://mw).hotlms.coin/16337-128 MICROWAVE JOURNAL
JANUARY 200S
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COVER FEATURE: NOW
or a 78 percent increase iti trackrange.^ '** CREE provides
commercialSiC hybrid devices putting out 10 to60 W'for lip to 4 GHz
luul GaN liy-hrid de\ices putting (iiit 15 to 120 Wfrom UHF to 40
GHz.'f^ Their goal isto provide in one package 550 Wpeak and 30 to
40 W average linearpower output using a single-stageFET. CREE
supports the design ofMMIC SiC and GaN cliips. For GaNMMIC tliey
provide 60 W saturated
from 2.5 to 4 GHz and 25 W saturat-ed from 5 to 6 GHz. See
References16-18 for detailed siin'ex'S of state-of-the-art on GaN
and SiG.'SiGe CHIPS
SiGe has tlie advantage of using Sias a su})strate. the
te'chnolog\' of thelow-cost, commercial integrated-cir-cuit
industry and whose exten.sive re-sources can be drawn upon. It
offersthe potential of liiglier performance
egraTECHNOLOGIES, INC.
TMP Rr PULSED POWER LEADER!
Integra's Miniaturized Power Amplifier (MPA) devices
arecompletely impedance matched to 50 ohms internal to thepackage.
The MPAL series utilizes gold metali2ed siliconLDMOS technology.
They are characterized for simple pulsedoperation (lOOus, 10%) with
low and constant quiescent current.They are capable of operating
under other pulsed operationalmodes and under other classes of
bias.
2.7 - 3.1 GHz and 3.0 3.5 GHz frequency bandsFlexible class of
operation: AB, B or AFlexible pulsed operational modes
Integra Technologies, Inc. 321 Coral Circle El Segundo, CA
902454620Telephone: (310) 606-0855 Fax:(310)606-0865
Copyr>glit 2007 All Righls Reserved ^."^
w w w . i n t e g r a t e c h . c o m ' ^ ^
at low cost. SiGe does not competewith GaAs with respect to
microwa\eoutput power or noise figure. It offerslow cost and the
ability to integratemany functions on a single chip. Inaddition to
microwave power ampli-fiers and a low-noise figure receiveron one
chip, it can have A/Ds anddigital circuitry. It can have CMOSon the
same chip. Si CMOS. GTRI is
TABLE IIGaN TECHNOLOGY ADVANTAGES
GaN lias the highest [xnu'r dciisih nlaiivexisting tec'hin)!og\'
enahlcs retiiEL-cil chip size - IDWI.T cost
tor a given power sni;il!er FET size enables broader
bantlwjdth because of higher impeditnceGaN capable nf higber
operating voltage
jn power systemGaN on SiC ha.s icondiicti\'ity eonipared
inaiiitain moderate efiiiiiriel ternps ;U high
TABLE IIIADVANTAGES OF MMIC GaN
OVER GaAi MMIC Provides .sy.steiii adMinlages re: weiglil,
coLiliiig. priiTie [lower, enst. sensitiviU', range 2H V vs. 10
Vat ix current (I) provides
5- Wx power witli - same gainiuid elik'ieniy as C.nAs
Iligl) voltage Ga/\s Pl'lEMT al 10 t(} 20 Vlit lower [ pro\ides
only ] .5 to 2x power.
CiiiN iu Hit)
- 1
47 390(Z)/490 (SiC)(WViii-K)
38 Visit http://niwj.hotims.coni/16337-65 MrCROWA\T. JOrRNAI.
JANl ABY 200S
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COVER FEATURE: NOW
CMOS CHIPSCMOS now operates at microwave
Ireqiiencies. It. too, uses a silicon suh-strate and is the
technology widely usedill the coinputtT iuthistrv. It Imlils
thfpromise of low cost and low powei' (orthe receiver parts of T/R
modules. LikeSiCe. it lias tlie advantage of allowinjjthe
integration of many functions on asiujrle chip, even more so than
SiGf.One ciiip can have RF, IF, haseljand.microprocessor, memory,
tunable filtersand A/Ds a .system on'a chip (SOC). Ittan be
c()ini)inetl with CaAs or GaN forthe microwave power amplifier and
lownoise flpue receiver. Using CaN has thead\antage oi beintj
robn.st euon^h that alimitrr may not be needed. Si to,tietlifrwith
CMOS offers the possibility- of theintegration of many receive
and/or tran.s-mit channels on a single chip.
DIGITAL BEAM FORMING (DBF)DBF hiLs am\ecl lor microwave .AESA
radars (see Figure
8). It provides many sipiificant advantages over anulojf
hramfomiing.' For large arrays I used to say DBF Is only being
DBF: Formt J beamipointing at jammerand one dt target
SLCOUTPUT
i) Addplivc-adaplive array (Brookner and Howell, Pro(\
developing a SiCk' single-chip T/R module for use in an.\I*;S.A
radar. Its initial design had a peak power of > 50inW using a
nvo-stage power amplifier (PA). Work is un-der way to achieve 1 W
peak by usingthree stages.'^ The cost per element ofan .AES.A using
such a module is expect-('
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COVER FEATURE: NOW
done at subarniy. This is no longer tnie.l-llta II;LS doiH' it
at thr element level tora 2.'5(X)-eIeinent iirray at S-band, a
nia-jor lireakthroitgh. Using DBF elimi-nates the analog
coinhinin
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COVER FEATURE: NOW
lobe. It is to adjust ndaptively the uin-plitiule aiul pliase
weisfhts of the arraySO as to put nulls in the directions oi"the
jammers while maintaining themain l)eam poiutin;[;in the reijuirt-d
di-rection. The.se amplitude and phaseweight adjustmeuts iire made
hitscd onthe jamming sigiKiIs recei\'eil b)' the ai'-ray and tlieir
ciJcnlated direction. Thissv'stem is kuouii as a luJly atlaptive
ar-ra)' processor". Here again it is useiul ttjview tlie fully
adaptive array froni an-
other physical point of \iew. Just as pre-viously we viewed the
SLX" as an arrav'that puts nulls in die direction of thejanuners.
we can now go the other wayand \ie\v the (ully adaptive
arrayprocessor iw a SLC.^'"
Fidiy adaptive arrays have beentoo (lifficiilt to implement for
largearrays up to uow. the luirdv\'iu-e andtile processing load
being too great,To reduce the complexity, eonsidera-tion lias been
given to doing fully
44 Visit http://mwj. hotims.com/16337-53
adaptive arniv proce.ssing at the sub-array level. This reduces
the numberoi elements from thousantis to a fewtens. This is what is
done on theUK's Multi-fuiictiou p]lectronit;LlIyScainied Adaptive
Hatlar (MESAIi)."
Witli ttie advaueti-s of DBF, it is nowpossible to think ol
aehieving the per-formance ot fully adaptive proci'ssiugwithout its
couiplexity. In fact, tlieequiviJent jammer suppressi(jn of a
ful-ly adaptive array without its computa-tion and transient
penalties can heachieved. This can be accomplishedwith
adaptive-adaptive array pnK*ess-irig.' This involves no more than
Itx-at-ing digitally where the jamnu'rs are.then ]K)intiug lieains
at tliesc jainiucrs(these beams are effectively
eigen-l)eams)^-'"-"* luid using these lu-iims asside lobe
cancellers for the uiaiu beam(see Figure 9). For a U)(K)-cleuit'iit
ar-ra\' having to cope with 10 jammers, wenow have to invert a 10 x
10 matrix in-stead of a KXX) X KXK) niatiix and thetransient time
is reduced iiy a factor ot100. lu a elas.siciJ full)' adaptive
arra),one does not make use of" tlie loctitionof the jammers. But
we can eiLsily de-termine their hjcation rather than toput on
biiudei's. Tliis method i.s e(julva-leut to the method of Principal
C o^tnjx)-nents.^ The jammers c;ui easily be lo-cated by doing a
Fast Fourier Trans-form aeross [he array This vvil[ notlocate
jammers less tliaii a Ix^anivvidthapart, but fbr uiany applications
it maybe g(K)d enough. If lietter jamuier VAU-ci'llation is needed,
then two stjuintedbeiuns about .'3/4 of a beamvvitlth apartcan be
used fbr each located jammer.Tliis is betmise for closely spaci'd
jam-mers, less tlian a beamvvidth apart, liteeigen}>eams are sum
and differencebeams."' Alternately the Music algo-ritlim can be
used.''^ Adaptive-adaptiveanay pnx-essing is in the .same spirit
iH.sthe knowledge aided techniquesDAHPA has been recently
fundingknown as Knowledge Aided SensorSignal Processor & Expert
System(K.\SSPFR).^^ which they have appliedto Space-time Adaptive
Proces.siug(STAP) discussed in the next section.
STAPSTAP is adaptive-an ay proee.s.siiip;
of a piil.se Doppler vvavefbrui. It pro-vides adaptive nulling
of ground clut-ter and jammers on a moving plat-(oriu. On a ino\ing
platfbrui it placesa 2-D Doppler-angle null where the
MICBOWAVE JOURNAL JANUARY 2008
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cluttfv is.^ STAP is being used on thenew carrier-based E2-D
AdvancedHawkeyes AN/APY-9 radar sliown inFignre l.'^ ^ It is used
in tlie littoralLTivironnifint.'''^ It can also be nsed tocancel
ont ground clutter tor agiound-based pulse Doppler radar.^'
PACKAGING AND ASSEMBLYIt is now possible to package and
assemble active pbascd arrays havinglow cost, li"hf weitiiit and
small \-ol-
nnie. The technique involves the useof coinniercial printed
wiring boards(PCB) and no packages for indi\idnalT/R modules. An
X-band building-block ana\' of" 128 elements and T/Rmodules was
built having a size of" 7.4X 10.1 X 0.21 in.2
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COVER FEATURE: NOW
to 18 GHz.3>-i'' The Georgia TeclinicalKesearch Institute
{GTRI) is devel-oping an urniy luiviniT; 33:1 instantii-nt'Oii.s
haiKKvicltli witli potential oi100: l.'^ "^TUBE ADVANCEMENTS
Tubes arc niakijig major ad-\ances. '- ' '-^ 2 Tlu'
a\'ailaliilily ofpovv-orful software now allows tlie
designt()ber20
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l.T. G.J. Frazer, Y.I. Ahraniii\ilc-li and B.A. 24.Joliiison,
"Spatially Wavcrorni DiverseUadar: Pcrspct-tives lor Ilifih
Fre(]iient:y 2.5.OTIIH." 0(17 lERR Radar Conferenoe,April 17-20.
2(XI7. Boston. MA. 26.
l(i. Vlilligmi, cl ;J., HnilarC'.on-2007.17. Kopp,/Wi3S. (.
:TH1. Hoiiziw Magazine. 2()6.39. Machine Design. Maaii 22. 2007.40.
R..^ , Moiiziiigo and T.W. Miller. Inlnxluc-
tion to Adaptive .-\rrr/(/.v. Jolin Wiley &Sons Inc..
I9SII.
41. M.f:. WVlls. "MK.SAH Arlapliv.- Nnlllng,"lEECiilloijuinni.
jnm-, 1990.
42. J. (iiifiri and J. Hrrpn. "Military- Hadar,"Jiinf 2.5-27.
2(X)7.
43. K. Tmt and li. Cnnirninjf.s. ct al.. Inti'nia-liorial
SynipcKsinni iiri Pila.scd-array Sys-tems anrl Technology, OttobL-r
2003,Boston. MA.
41. S. Brierle); Raj'thcon Co.Eli BrookfMr nv-rtiM't/
ltl\tii:ii: '/-ij/.v fi-fi Til,' citiiC