spatial combiners using dense finline arrays in oversized...
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Spatial Combiners using Dense Finline Arrays in Oversized Waveguides
Robert A. YorkVicki ChenP.C. JiaEric G. Erker
University of California, Santa Barbara
UCSBDepartment of Electrical and Computer Engineering
MURI
Project Goals and ProgressProject Goals and Progress
Broadband Power CombinersBroadband Power CombinersDense finline array architecture
Considerations for Large Combiner SystemsConsiderations for Large Combiner SystemsEfficiency, Noise, Statistical Errors
Scaling to mmScaling to mm--wave frequencieswave frequenciesOversized waveguide and implicationsDevice technologyK-band demo with flip-chip devicesKa-band MMIC system
MultiMulti--Octave DesignsOctave DesignsOversized coax4-16GHz Combiner demo
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Gradual transition Gradual transition from WR42 to the from WR42 to the oversized oversized waveguidewaveguide
Oversized waveguide
(TE10,TE20)
Active Devices
Tapered-FinlineAntennas
Scaling Scaling Finline Finline Combiner to mmCombiner to mm--wavewave
•• System is built in the oversized waveguide environment to System is built in the oversized waveguide environment to accommodate more devicesaccommodate more devices–– TE10, TE20 modesTE10, TE20 modes
•• Using Using finlinefinline to CPW line Transition to eliminate bondto CPW line Transition to eliminate bond--wires for high wires for high frequency applicationsfrequency applications
•• Monolithic Circuit Design with flipMonolithic Circuit Design with flip--chip bonding of the active devices chip bonding of the active devices --FCICFCIC
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Oversized WaveguideOversized WaveguideCharacterized by 6 cards measurementCharacterized by 6 cards measurement
Systems was built for Systems was built for 18GHz to 22GHz18GHz to 22GHz
TE10TE10 TE20TE20
XX
yy
Symmetrical loading is necessary to suppress the TE20 mode.
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0
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S11 Through [dB]S21 Through [dB]50 ohm load
Frequency [GHz]
TE30 mode starts TE30 mode starts to propagateto propagate
Only TE10 mode should Only TE10 mode should be propagatingbe propagating
2 cm2 cm
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Antenna (Antenna (Finline Finline Transition) DesignTransition) Design
Reference paper: Design of Waveguide Finline Arrays for Spatial Reference paper: Design of Waveguide Finline Arrays for Spatial Combining. Submitted to IEEE transaction on MTTsCombining. Submitted to IEEE transaction on MTTs
Klopfenstein TaperKlopfenstein Taper
CPW lineCPW line
••Design is based on the optimal Design is based on the optimal taper of the Xtaper of the X--band system.band system.
••Finline to CPW line transitions Finline to CPW line transitions ––Eliminate the bondEliminate the bond--wire for high wire for high frequency applications. frequency applications.
••The ground plane is attached The ground plane is attached directly to the waveguide walls to directly to the waveguide walls to provide a good Input/Output provide a good Input/Output isolation. isolation.
••Use HFSS for simulation.Use HFSS for simulation.Ground
signal
AlN substrate
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Combining EfficiencyCombining Efficiency
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0
18 18.5 19 19.5 20 20.5 21 21.5 22
S11-2 cards [dB]S21-2 cards [dB]S11-1 card [dB]S21-1 card [dB]
Frequency (GHz)
Measurement for one card (asymmetrical) and two cards (symmetrical) system
•• Symmetrical loading is necessarySymmetrical loading is necessaryto avoid TE20 mode and achieve to avoid TE20 mode and achieve efficient combining.efficient combining.
•• ~ 76% combining efficiency is ~ 76% combining efficiency is achieved.achieved.
•• Efficiency can be improved by Efficiency can be improved by further optimization of the taper further optimization of the taper shape to reduce reflection loss.shape to reduce reflection loss.
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0
18 19 20 21 22 23 24 25 26
S21 MAG [dB] 2cardsS21 MAG [dB] 4cardsS21 MAG [dB] 6 cards
Frequency [GHz]
The effect of asymmetrical loadingThe effect of asymmetrical loading
Design Bandwidth
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KKKK----band SSPA Benchmark Databand SSPA Benchmark Databand SSPA Benchmark Databand SSPA Benchmark Data
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0.1 1 10
HRL K4 (Amplifier)HRL K4 (Load Pull)HRL K3TRWTIMartin mariettaAvantekMIT
Power Added Efficiency, %
Output Power, Watts
1996 Industry Trend
18 GHz Power Devices: Industry ComparisonSource: Mike Delaney, Hughes Space & Communications, El Segundo, CA
Path to Broadband Power• High efficiency favors small-area devices• Broad bandwidth favors small-area devices• Lower phase noise favors large number of devices
Conclusion:Conclusion:Use a large number of small devices for broadband power
Efficient broadband combining of many devices favors spatial combining
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10 100
Com
bini
ng E
ffic
ienc
y (%
)
Number of Amplifiers, N
Binary Corporate
Parallel (Spatial)
α =0.1dB
α =0.2dB
α =0.3dB
So=0.5dB
So=1.0dB
So=1.5dB
2 20
25
30
35
40
45
50
0.1 1 10
Sys
tem
PA
E, ηη ηη
sys %
Power, Pa [Watts]
So=0.5dB
So=1.0dB
So=1.5dB
α=0.3dB
α=0.1dB
α=0.2dB
Pout=40 Watt
Binary Corporate
Parallel (Spatial)
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One Stage Hybrid FlipOne Stage Hybrid Flip--ChipChipAmplifier DesignAmplifier Design
FiltronicSolidStateLP1500
ResistorUsed for low Frequencystabilization
Dielectric cross-over
Processing includes:Processing includes:•• TransmissionTransmission--line patterning (3um Au)line patterning (3um Au)•• Resistive layer etching Resistive layer etching •• ThinThin--film capacitor (Ti 200A, SiN/PECVD film capacitor (Ti 200A, SiN/PECVD
3000A) 3000A) •• Metalization for capacitors (Au 4000A)Metalization for capacitors (Au 4000A)•• Bonding Pads for pHEMT (Au 6um)Bonding Pads for pHEMT (Au 6um)•• Dielectric crossDielectric cross--over for CPW line ( over for CPW line (
PMGI underneath)PMGI underneath)•• FlipFlip--Chip Bonging of the pHEMT device. Chip Bonging of the pHEMT device.
Thin-film Cap
The amplifier is designed atThe amplifier is designed at
20GHz, using HP EESOF/ADS for simulation.20GHz, using HP EESOF/ADS for simulation.
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5
5.5
6
6.5
7
16
18
20
22
24
26
28
10 12 14 16 18 20 22
Gain-amplifier
Pout-amplifier
Pin (dBm)
0
2
4
6
8
10
Frequency (GHz)16 16.5 17 17.5 18 18.5 19
8 different amplifiers
One Stage AmplifierOne Stage Amplifier
Power measurement•• 6 dB power gain with 26dBm 6 dB power gain with 26dBm
output power.output power.•• 8 different amplifiers were 8 different amplifiers were
measured to show that they measured to show that they are identical.are identical.
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KK--band Active Antenna Tray Layoutband Active Antenna Tray Layout
TransitionTransition
Bias lineBias lineAmplifierAmplifier
8.6mm
13.7mm
•• 4 amplifiers per tray.4 amplifiers per tray.•• Amplifiers are biased in pairs.Amplifiers are biased in pairs.•• Single substrate monolithic designSingle substrate monolithic design
•• Heat conduct through substrate to Heat conduct through substrate to waveguide fixturewaveguide fixture
Problems encounteredProblems encountered•• Bias line is too lossy and needs to be reBias line is too lossy and needs to be re--designed.designed.•• Amplifiers should be biased individually to insure operating in Amplifiers should be biased individually to insure operating in the same conditions.the same conditions.•• A preA pre--amp is needed for higher gain and better efficiency.amp is needed for higher gain and better efficiency.
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Combiner System During MeasurementCombiner System During MeasurementAROMURI
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-5
0
5
10
18 18.5 19 19.5 20
S11 MAG [dB]S21 MAG [dB]S22 MAG [dB]
Frequency [GHz]
Results for 2x4 System
Small signal result for 2x4 systemSmall signal result for 2x4 system
•• Preliminary result for 2x4 systemPreliminary result for 2x4 system•• 2.4dB of system loss in through2.4dB of system loss in through--
line measurementline measurement•• 2 Watts output power2 Watts output power
Power measurementPower measurement
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0
2
4
15
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30
35
10 15 20 25 30 35 40
Gain-8vGain-8.5vGain-9v
Pout-8vPout-8.5vPout-9v
Pin (dBm)
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Amp4Amp3Amp2Amp1
16 17 18 19 20 21 22Frequency (GHz)
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100
50
0
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Phase Errors due to Processing
Amp1
Amp2
Amp3
Amp4
Processed on different substrates
•• For circuits processed on the For circuits processed on the same substrate, the phase same substrate, the phase difference are negligible.difference are negligible.
•• For circuits built on different For circuits built on different substrates, the phase substrates, the phase difference is about 35 degree difference is about 35 degree which could cause severe which could cause severe problems for the combiner.problems for the combiner.
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Statistical Errors in ArraysStatistical Errors in Arrays
G
G
G
Input Output
Amplifiers
Ain Bout
Split
ter
Com
bine
r
ain,1 bout,1
ain,2 bout,2
ain,N bout,N
GG
GG
GG
Input Output
Amplifiers
Ain Bout
Split
ter
Com
bine
r
ain,1 bout,1
ain,2 bout,2
ain,N bout,N
0
1
(1 ) i
Nj
out i ii
AGB r G eN
δϕδ=
= +∑
( )2
1 10
1 (1 )(1 ) i jN N
ji j i j
i j
P rr G G eP N
δϕ δϕδ δ −
= =
= + +∑∑
( )2 22 2 2
0
1 1e e e
PP e P G P e
P Nδϕ δϕδ− − = + + −
Output voltage:
Output Power: 20 0( )P AG=2
outP B=
Change in power due to errors:
Ensemble average:
Ref: R. York, “Some considerations for Optimal Efficiency and Low Noise in Large Power Combiners”, submittedto IEEE Trans. Microwave Theory Tech.
Phase errors and device failures are most important in large combiners
i er P=ri = 0 or 1Probability of device survival
Loss, Gain, PAELoss, Gain, PAELoss, Gain, PAELoss, Gain, PAE
dca
ia
dca
iaoaa P
PGP
PP )1( −=−=η
Single Amplifier Cell
N-way Combiner System
Splitter CombinerPia
G
Poa
Pdca
Li Lo
Pi Po
ai
oi
dca
ioi
dc
iosys GL
GLLNP
PGLLP
PP ηη)1()1()1(
−−=−=−=
Pia
G
Poa
Pdcagainhigh for oasys Lηη →
Conclusions: →→→→ Output losses alone determine ultimate performance of a combiner→→→→ Input losses can be overcome by high-gain pre-amplification
PAE of pre-amplified system can easily approach combining efficiency based on output losses only
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4 6 8 10 12 14 16 18 20
Nor
mal
ized
Sys
tem
PA
E (
%),
ηsy
s/ηa
Power Amplifier Gain (linear), G
Li = L
o=-0.2 dB
Li = L
o=-0.5 dB
Li = L
o=-1.0 dB
Eqn (3)
Eqn (4)
(3)
(4)
Two Stage Amplifier DesignTwo Stage Amplifier DesignFor High Efficiency combiningFor High Efficiency combining
Input matchingInter-stage matching network Output matching
LP6836LP1500
Vd1 Vd2
Vg1 Vg2
•• A preA pre--amp is added to amp is added to provide higher gain.provide higher gain.
•• The output power should The output power should remain the same as the remain the same as the oneone--stage amplifier. stage amplifier.
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0
10
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30
0 5 10 15 20 25 30
S21 MAG [dB] - thin SubstrateS21 MAG [dB] - 2 layers sub
Frequency [Hz]
Two-Stage Amplifier Measurements
• The quasi-TEM mode is excited by discontinuities in the circuit. • The increase of complexity of the circuit may increase the possibility of the
mode excitation. • The glitches are eliminated by adding a spacer underneath the AlN. • Reducing the size of the CPW-line could reduce the mode excitation, but
increase the insertion loss.
Quasi-TEM
εεεεeff
εεεεAlN
εεεεAlN > εεεεeff > εεεεAir
εεεεeff
εεεεAlN
εεεεspacerεεεε’
εεεε’ > εεεεeff The Quasi-TEM mode is forbidden
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Amplifier arrayAmplifier array••powerpower••bandwidthbandwidth••efficiencyefficiency••stabilitystability
TriplersTriplers••bandwidthbandwidth••efficiencyefficiency
EnclosureEnclosure••thermal managementthermal management••modingmoding
AntennasAntennas••Impedance matchingImpedance matching••Field distributionField distribution
ff00
MMMM--wave Power Modules using wave Power Modules using Combiner/Tripler StructureCombiner/Tripler Structure
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3f3f00
Coaxial Combiner Concept
OuterConductor
InnerConductor
Type N(DC-18 GHz)Connector
1.77''6.067'' Inner Conductor Diameter 0.092 ' 'Outer Conductor Diameter 0.210 ''
1.2 ''
0.4 ''
Tap ere d Tap ere d Sloten na
MM IC Amplifier
SlotAnt en na
MM IC Amplifier
line
•• Broadband tray schemeBroadband tray scheme•• OverisizedOverisized coax coax accomodates accomodates
more devicesmore devices•• No lower cut off frequencyNo lower cut off frequency•• Easier for modeling and Easier for modeling and
optimizationoptimization•• Symmetric structure, uniform Symmetric structure, uniform
power drive, good linearitypower drive, good linearity
Modeling of Coaxial Slotline Array
•• WaveguideWaveguide is divided into 32 is divided into 32 sections due to symmetry, and sections due to symmetry, and Perfect Magnetic condition (PMC) Perfect Magnetic condition (PMC) is applied at both sideis applied at both side
•• A Perfect Electric Condition A Perfect Electric Condition (PEC) is applied to divide each (PEC) is applied to divide each section into 2 unit cells, section into 2 unit cells, each one each one has the same outer radius to has the same outer radius to inner radius ratioinner radius ratio
•• Conformal mapping maps unit Conformal mapping maps unit cell to an equivalent parallel plate cell to an equivalent parallel plate waveguidewaveguide
11.25o
11.25o
PEC
PEC
PMC PMC
PEC
PEC
PMC PMC
50 Ohm termination
Lt
Slotlinetaper
y
b
ad
y
x
z
SDM Simulation ResultSDM Simulation Result
0 .2 0.4 0 .6 0 .8 1n o rm a lize d s lo t
0 .5
1
1 .5
2
2 .5
3
3 .5
evitceffeytivitti
mrep
0.2 0.4 0.6 0.8 1 normalized slot
0.5 1
1.5 2
2.5 3
e v i t c e f f e
y t i v i t t i m r e p
(a)
7GHz
12GHz
b
g
0 ac
x
y
16GHz
4 GHz
εr
εr
Normalized slot
3.5
(b)
•2x2 finline array in standard WR-90 waveguide
•Coaxial waveguide structure show little dispersion
•Propagation constant (effective permittivity) calculated for expected slot widths and frequencies using SDM
AgilentAgilent HFSS Simulation ResultHFSS Simulation Result
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0 5 10 15
Simulation Result of SDM and HFSS
S11_HFSS [dB]S11_SDM [dB]
Freqency [GHz]
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0
0 6 12 18
Second and Third Harmonics
S11_2nd [dB]S11_3rd [dB]
Freqency [GHz]
•• Unit cell analysis with PMC sidewallUnit cell analysis with PMC sidewall•• Simulation shows bandwidth from 4 to 18 GHzSimulation shows bandwidth from 4 to 18 GHz•• The high order modes are The high order modes are surpressedsurpressed by the by the
intense loading and lower than intense loading and lower than ––22 dB22 dB
50 Ohm Termination50 Ohm Termination
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0
5
0 6 12 18
Reflection Coefficient of 32 Tray and 16 Tray Combiner
S11 _16 Tray [dB]S11_32 Tray [dB]
Frequency [GHz]
•• 2 slots in each taper2 slots in each taper•• 50 Ohm resistors are bonded at 50 Ohm resistors are bonded at each end of the tapereach end of the taper
•• Taper Length is 20 mmTaper Length is 20 mm•• Bandwidth is from 4 to 18 GHzBandwidth is from 4 to 18 GHz•• Both 16 tray and 32 tray Both 16 tray and 32 tray systems have the same systems have the same reflectionreflection
•• Dominated by the reflection Dominated by the reflection from bond wirefrom bond wire
50 Ohm Single Wrap Resistor
Coaxial Waveguide Power Combiner Coaxial Waveguide Power Combiner Loaded with 32 Loaded with 32 MMICsMMICs
Input Waveguide Transition
Output Waveguide Transition
Loaded Section
Circuit Tray
Bias Lines
Output TaperMMIC
Bias Capacitor
Input Taper
Bias Pads
Connector to Power Supply
Coaxial Power Combiner PerformanceCoaxial Power Combiner Performance
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0
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0
5 10 15
16 Tray Coaxial Combiner's Reflection Coefficient
S11 [dB] S22 [dB]
Frequency [GHz]
0
5
10
15
20
0
5
10
15
20
5 10 15
Gain of the 16 Tray Combiner and MMIC
S21_Combiner [dB] S21_MMIC [dB]
Frequency [GHz]
••16 Tray (32 MMIC) coaxial combiner for testing16 Tray (32 MMIC) coaxial combiner for testing••3dB Bandwidth from 3.5 3dB Bandwidth from 3.5 -- 15 GHz15 GHz••S11 lower than S11 lower than ––8dB over the whole band8dB over the whole band••Loss consistent with the passive structureLoss consistent with the passive structure••Lower cutoff set by antenna designLower cutoff set by antenna design••Upper cutoff due the MMIC responseUpper cutoff due the MMIC response
Power MeasurementPower Measurement
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0
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15
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5 10 15 20 25
Power Sweep @ 10 GHz
Output Power [dB] Gain [dB]
Input Power [dBm]
15
20
25
30
35
-5
0
5
10
15
2 4 6 8 10 12 14 16
Output Power and Gain @ Pin=20 dBm
Frequency [GHz]
••1 W output at 10 GHz at 1 dB compression1 W output at 10 GHz at 1 dB compression••32 MMICs in total32 MMICs in total••MMIC output 16 dBm at 1 dB compressionMMIC output 16 dBm at 1 dB compression••<1 dB output loss<1 dB output loss••~80% combining efficiency~80% combining efficiency
Phase Noise Measurement SetupPhase Noise Measurement Setup
UCSB AmplifierUCSB Amplifier
Courtesy Will Caraway, AMCOMCourtesy Will Caraway, AMCOM
SourceSource
TWTTWT
PowerPowerSupplySupply Noise Noise
Test SetTest Set
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-60
-40
102 103 104 105 106
SSB
Noi
se P
ower
, dB
/Hz
Frequency Offset, Hz
Phase Noise MeasurementPhase Noise Measurement
40W X40W X--band Combiner Systemband Combiner System
Courtesy Will Caraway, AMCOMCourtesy Will Caraway, AMCOM
• Measurements in progress• Awaiting single-device measurement
Conclusions• Scaling to mm-wave frequencies
Dense loading suppresses high order modeSymmetric loading suppresses odd modesPhase errors
• K-band PrototypeDemo with flip-chip amplifiersMMIC version under development
• Coaxial PrototypeUniform drive, incorporate many devicesTwo-octave Demo with low-power TWA MMICs
• Some “fundamental” issues exploredInfluence of device size and gainInfluence of statistical errors
• Future workNoise & Linearity characterization underwayIncreased power densityIncorporate triplers/phase shiftersIncorporate GaN devices (ONR MURI)
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