The University Of Cincinnati College of Engineering

WidebandReconfigurableHarmonicallyTunedGaN SSPAforCognitiveRadios

Seth W. WaldsteinThe University of Cincinnati-Main Campus

Miguel A. Barbosa KortrightUniversity of Puerto Rico, Mayagüez Campus

Rainee N. SimonsNASA Glenn Research Center

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Introduction - MotivationBenefits&ChallengesWide-BandReconfigurableHarmonically TunedPowerAmplifier

• InverseClass-FDesign• AmplifierFabricationandResults• ThermalManagement• Dual-BandMulti-NetworkDesign

PowerVariability• HybridCoupler• BalancedAmplifier

Conclusions andAcknowledgements

Outline

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Whatcapabilities doweneedfromatransmitpoweramplifiertoenableacognitivecommunication system?I. Re-configurability

• Highoutputpower;withoutsacrificing efficiency• Operatingfrequency;withoutsacrificing efficiency

II. Linearity

Introduction- Motivation• Congestion,causedbyagrowingusercommunity attheX-Bandspace-to-grounddatalinkfrequencyrange,iscreatingtheneedforcognitiveradiocapabilities.

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BenefitsHigherEfficiencyMeans

• SavedDCpower• DecreasedExcessHeat

• Efficiency islostprimarilythroughpowerdissipationwithinthetransistorjunctionandconductorlosses.

• ImprovedThermalReliabilityOurproposedinnovationhasthepotentialtoenablelowcostCognitiveCommunicationSystems:

• AvoidstheneedformultipleTx andRx modulesApplicationsinclude:

• NASAMissions• SmallSatellitesandSpacecraft• MilitaryUnmannedAirVehicles• Commercial/AmateurCubesats

DecreaseinHeatSinkMass

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Challenges

WidebandDevices• Class-FtypewidebandharmonictuningtechniquesusedatlowerfrequenciesareunrealizableatX-band

PowerVariability• Amplifiersefficiencydropswhenbackedofffromsaturation

GaN TransistorFrequencyLimitation• AchievingmaxPAEwithClass-FtypeamplifiersrequiresFT >3rd harmonic• CurrentcommerciallyavailabletransistorshaveanFT of18GHz(≈ 2nd Harmonic at X-Band)

• HighFT ofGaN HEMTscomesattheexpenseoffeaturesizeandpowerdensity

Efficiency• HighEfficiencySSPA’srequireharmonictuning- suchasClass-FandInverseClass-Fdesigns.Matchingcircuitiscomplexandinherentlynarrowband.

CircuitWithinthisareacanberealizedusinglowcostCMOS

technology

*IMN(InputMatchingNetwork)*OMN(OutputMatchingNetwork)*ISW(InputSwitch)*OSW(OutputSwitch)

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Wide-BandReconfigurableHarmonicallyTunedPA

Lowfrequencydampingcircuit

2nd harmonicshort

λ/4@fundamental

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InverseClass-FGaN SSPAatX-Band

Harmonicsarereflectedtoreshapethevoltageandcurrentwaveformatthedrain

Current(mA)

Voltage(V

)

Transistor

X-Bandisselectedbecausethe8.0-8.5GHzfrequencyrangeisdesignatedforNEN

space-groundlinks

OurtargetisPout >4-WwithPAE>35%

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FabricatedInverseClass-FAmplifier

Substrate height, h = 0.02 inch & 𝝴r = 3.0

Tran

sist

or: C

ree

CG

HV1

F006

S 6W

, DC

-18

GH

z, 4

0V, G

aNH

EMT

RF Output

Low Freq. Stability Circuit

Parallel RL Gate Bias

Choke

GaNTransistor

RF Input

DC Drain Bias

DC Gate Bias

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TuningofInverseClass-FAmplifier

SchematicoftheinverseClass-Famplifierdesign.

SimulatedandMeasured(Γopt-in)parametersofIMNaftertuningfrom8.4to16.8GHz.

SimulatedandMeasured(Γopt-out)parametersofOMNaftertuningfrom8.4to16.8GHz.

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Maximum Pout = 5.14-W, PAE = 38.6% with DE = 48.9%

MeasuredPout andPAEvs.Pin VDS=40V,VGS=-3.2Vandfrequency=8.45GHz.

MeasuredgainandVSWRvs.Pin ;VDS=40V,VGS=-3.2V,andfrequency=8.45GHz

InverseClass-FPout,PAE,GainandVSWR

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InverseClass-FBandwidth

70 MHz bandwidth where Pout > 36 dBm and PAE >

35%8.315 - 8.385 GHz

PAE and Pout vs. Frequency VDS = 40 V, VGS = -3.2 V; Pin ranges 21.5-30.35 dBm, VSWR ranges 2.4 -33

70 MHz

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Freq. (GHz) Pin (dBm) VDS (V) Gain(dB) PAE(%) Temp(°C) Pout (W)8.36 29.9 32 6.3 37.3 95 4.2

ThermalManagement

CW operation required direct contact between

transistor belly and heat sink

Operating conditions of measured package temp = 95°C :DC Power Dissipation ≈ 7 W

• Data sheet indicates for package temperature of 95°C, the max allowed power dissipation is ≈ 9 W.

Hence, achieved thermal safety margin of ≈ 22%.

Operating conditions observed

through thermal imaging

Switch1(GaAs)

X-BandMN

S-BandMN

Switch#2(PIN

Diode)

X-BandMN

S-BandMN

DiplexerInputPort

⊪

GaNHEMT

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DualBandMulti-NetworkDesign

Reconfigurableconceptcanbeappliedtodual-band transmitters

Diplexer

DualBandAntenna

CONTROLLER

COGNITIVERADIO

PROCESSOR

DC BIAS SUPPLY

Amp#1

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Amp#2

3-dB Hybrid Coupler 3-dB Hybrid Coupler

Output

Isolated

Input

Isolated

Port#1

Port#2

Port#3

Port#4

PowerVariability- BalancedAmplifier

BalancedAmplifierCircuitTopology

Microstrip Branch Line 3-dB Hybrid Coupler

InputPort #1

IsolatedPort #2

OutputPort #3

OutputPort #4

Substrate height, h = 0.02 inch & 𝝴r = 3.0

Measured vs Simulated Results

InputPort #1

OutputPort #4

IsolatedPort #3

IsolatedPort #2

MMICAmplifiers

Substrate height, h = 0.02 inch & 𝝴r = 3.0 16

Hybrid Couplers

FabricatedBalancedAmplifier

Mini-Circuits GVA-123+, GaAs

HBTs

Pin vs. Pout for Single & Balanced MMIC Amplifiers

-10

-5

0

5

10

15

20

25

-19.

3-1

7.3

-15.

3-1

3.3

-11.

3-9

.3-7

.3-5

.3-3

.3-1

.3 0.7

2.7

4.7

6.7

8.7

10.7

12.7

14.7

Pou

t(d

Bm

)

Pin (dBm)

Frequency = 8.546 GHz

Balanced Amplifer Single Amplifier

+3dB

Balanced amplifier provides a 3dB increase in output power over a single

MMIC

MeasuredPout vs.Pin withVD=5 Vandfrequency =8.546GHz.

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Conclusion• Challenges have been presented for achieving the desiredhigh efficiency wide-band operation of a transmit poweramplifier at X-band

• A reconfigurable harmonically tuned SSPA has beenproposed as being a solution to enabling wideband highefficiency needed for a cognitive system

• An inverse Class-F GaN SSPA operating at 8.4 GHz has beenshown to achieve 5.14-W of output power with 38.6% PAEand a 70 MHz bandwidth of Pout > 36 dBm and PAE >35%.

• A balanced amplifier has been presented for additionalconsideration in reconfigurable power topologies.