ARO

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ARO MURI
K-band Spatial Power Combiner Using Active Array
Modules
LY. Vicki Chen, PengCheng Jia, Robert A. York
PA Workshop, San Diego 2002
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Presentation Outline

• Passive System
• Antenna array, Higher order mode problem,
  Performance
• Amplifier Design
• Two-stage Amplifier, Flip-Chip IC, CPW-line
• Power Combiner
• Design considerations, Performance
• Conclusions

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Spatial Power Combining
ARO MURI

• Normal incident/outgoing waves
• Limited bandwidth in general
• Easier for monolithic design
• Challenge in thermal management

Tile Approach

• Parallel incident/outgoing waves
• Broadband characteristics
• Good heat-sinking property
• Consuming more substrate area

Tray Approach
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System Overview
ARO MURI

• Extended work from the X-Band Spatial Combiner
  Design
• Oversized Waveguide Environment TE10, TE20 from
  18 to 22GHz
• Fin-line to CPW line Transition
• Monolithic Circuit Design Flip-Chip IC

Oversized waveguide (TE10,TE20)
Gradual transition from WR42 to the oversized
waveguide
Active Devices
Tapered-Finline Antennas
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ARO MURI
Antenna Design
Finline to CPW line transitions

• Design is based on the optimal taper design of
  the X-band system.
• Finline to CPW line transitions Eliminate the
  bond-wires.
• Air-bridges are needed to provide good grounding
  in the middle ground plane.
• Use HFSS for simulation.

Klopfenstein Taper
Ground
Signal
Ground
Signal
Ground
CPW line
AlN substrate
Reference paper Design of Waveguide Finline
Arrays for Spatial Combining. Submitted to IEEE
transaction on MTTs
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HFSS Simulation
By forcing the PMC boundary condition, the even
mode does not exist in the system.
PEC
PEC
metal
air
Et
Et
metal
PEC
Fin-line
Metal
PMC
PMC
Dielectric

• Simulate for 2x4 system.
• Simplify the problem by applying the boundary
  conditions.
• Impedance Gamma vs. Gap-size
• Finline CPW Transition
• Reflection coefficient for the taper design.

Et
Waveguide Wall
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Effects of Mounting Grooves
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Single mode unilateral finline
The mounting grooves affect the optimal values of
many parameters
d

• Operating frequency
• Effective dielectric constant
• Substrate thickness

b
Small slots are affected more severely than
broader slots.
Reflection Coefficient (dB)
short circuit grooves
The depth of the short circuit grooves has huge
effect on the return loss
d?/5 d2?/15
d
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Combining Efficiency
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• Symmetrical loading is necessary to avoid TE20
  mode and achieve efficient combining.
• 76 combining efficiency is achieved.

6 cards (4x6 system) 50ohm Termination
Through-line measurement
Measurement for one card (asymmetrical) and two
cards (symmetrical) system
Frequency (GHz)
Frequency (GHz)
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Two-Stage Amplifier Design Flip-Chip Technology
using CPW-line
ARO MURI

• Thermal Management FCIC
• Gain Enhancement pre-amplifier
• Optimal load matching
• ADS/Momentum Simulations

Power device
Pre-amp

• Design Challenges
• Substrate modes are excited easily.
• Biasing circuitry is complicated.
• Good grounding should be maintained.

13.5mm
Ground
Signal
8.56mm
Ground
Signal
Ground
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Two-Stage Amplifier Design CPW-line Substrate Mode
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Substrate mode is excited easily!
Increasing the substrate thickness or reducing
the width of the CPW-line could reduce the effect
of the substrate mode.
?AlN gt ?eff gt ?Air
?eff
?AlN
Quasi-TEM
S21(dB) of the Two-stage Amplifier
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Two-Stage Amplifier Performance
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• Return loss lt-10dB for the operating frequencies.
  
• 27.3dBm output power with 20 PAE and 9.5dB power
  gain was obtained.
• Thin film (on-chip) and chip capacitors were both
  needed for biasing circuitry.

Pout
PAE
Gain
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Combiner Performance Two Cards Measurement
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• Small Signal Performance Power Measurement _at_
  18GHz
• Two cards system (8 amplifiers) with 34dBm output
  power.
• 12.5 PAE 62 Combining Efficiency (optimal
  76)
• Phase difference between cards degrades the
  output performance the most.

Pout (dBm)
PAE
Gain (dB)
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Measurement
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Statistical Errors in Arrays
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Output voltage
G1
Bout
A
G2
Splitter
Combiner
Probability of device survival
ri 0 or 1
GN
Output Power
Change in power due to errors
Ensemble average
Phase errors and device failures are most
important in large combiners
Ref R. York, Some considerations for Optimal
Efficiency and Low Noise in Large Power
Combiners, IEEE Trans. Microwave Theory Tech.
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Combiner Performance 6 Cards Measurement
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• Six Cards System (6x4) 2 devices failed.
• 10dB small signal gain.
• Absorbing material were added to prevent the
  in-band oscillations.
• Each cards was biased individually.
• Improper grounding could result in oscillations.
  
• Some chip resistors were added to prevent
  bias-line oscillations.

Signal cross-talk between bond-wires could induce
in-band oscillations
Absorbing Material
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Phase Noise Reduction
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G
Amplifiers degrade phase noise due to internal
nonlineariities which up convert low-frequency
amplitude and phase noise to the carrier
G
Splitter
Combiner
G
Noise contributed by the ensemble is reduced by
1/N (-13.4dB) compared with a single amplifier
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Power Measurement
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Non-uniform excitation profile

• 37.3dBm output power _at_18GHz was obtained.
• Non-uniform excitation.
• Chip resistors were added for bias-line
  stabilization.
• Combining Efficiency 53.7.

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Conclusion
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• Passive combiner achieved 76 combining
  efficiency.
• 34dBm output power has been obtained for 2-tray
  system.
• 62 combining efficiency was obtained.
• 37.3dBm output power has been obtained for 6-tray
  system.
• 53.7 combining efficiency was obtained.
• Phase noise reduction compared with single
  amplifier.
• Stabilization should be maintained for all
  frequencies.