A Phase Noise Study on Coupled Oscillator Arrays

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A Phase Noise Study on Coupled Oscillator Arrays

• Summer 2002 SURE Program
• Jack Chao, Univ. of Michigan - Ann Arbor
• Advisors Dr. L. Wilson Pearson, Chris Tompkins

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Outline

• Basic concepts
• Circuit fabrication
• Phase noise measurements
• Conclusions
• Future work

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Beam Steering

• Rotate beam axis by changing phase delay between
  elements

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Motivation

• Beam steering currently uses phase shifter for
  each element
• Becomes complex for large arrays at millimeter
  wavelengths
• Coupled oscillator arrays less complex circuitry
  for beam steering

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Coupled Oscillator Array

• Phase difference between adjacent oscillators can
  be controlled
• Less complex circuitry for beam steering

Antennas
Oscillators
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A Problem Phase Noise

• Problem All oscillator signals have phase
  fluctuation (phase noise or jitter)
• Proposed solution Injection lock at multiple
  points in array

• Summer objective verify multi-point injection
  locking reduces phase noise

H.-C. Chang, et. al., Phase Noise in
Externally Injection-Locked Oscillator Arrays,
IEEE Trans. Microwave Theory Tech., vol. 45, pp.
2035-2042, Nov. 1997.
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Injection Locking
Injection Locking a Single Voltage-Controlled
Oscillator
Free Running
Signal Injection
Injection Locked
Oscillates at ?0 More Phase Noise
Oscillates at ?1 Less Phase Noise
External Signal at ?1 (?1 close to ?0)
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Fabrication

• Oscillator layer (oscillates 10 GHz)
• Non-overlapping oscillation ranges
• Settled on 5-element array instead of 9-element

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Fabrication (contd)

• Transmit layer

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Injection Locking Setup

• Elements 3,5,7 were injection locked in various
  combinations
• Antenna received arrays combined signal

Antennas
Oscillators
3
5
7
Phase-shifters
Clean Source Signal
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Measurement Process

• Find arrays free-running frequency
• Tune individual oscillators
• Injection lock desired oscillators
• Measure phase noise for each injection combination

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View from Spectrum Analyzer
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Results - Injection Schemes
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Results - Injection Power
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Conclusions

• Experimentally verified increasing number of
  injection ports decreases phase noise
• Diminishing returns with increase in ports
• Increasing injection power decreases phase noise
• Greater effect on phase noise with less ports

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Future Work

• Lower noise floor of measurement setup
• Measure phase noise for 5-element array under
  beam steering conditions
• Debug and test entire 9-element array
• Fabricate and test two-dimensional array

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Acknowledgements

• Dr. Jim Harriss
• Xing Wang

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Questions?