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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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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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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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

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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

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22

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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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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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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

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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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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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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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Simulation Result of SDM and HFSS

S11_HFSS [dB]S11_SDM [dB]

Freqency [GHz]

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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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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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16 Tray Coaxial Combiner's Reflection Coefficient

S11 [dB] S22 [dB]

Frequency [GHz]

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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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Power Sweep @ 10 GHz

Output Power [dB] Gain [dB]

Input Power [dBm]

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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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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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