a phase noise study on coupled oscillator arrays summer 2002 sure program jack chao, univ. of...
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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
Beam Steering
Rotate beam axis by changing phase delay between elements
Equal-Phase Planes
Phase-DelayedInput Signals
AntennaArray
Beam Axis
Broadside(if all phases
equal)
Antennas
Oscillators
Coupled Oscillator Array
Phase difference between adjacent oscillators can be controlled
Less complex circuitry for beam steering
*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.
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
Injection Locking
Injection Locking a Single Voltage-Controlled Oscillator
Free Running Signal Injection Injection Locked
Oscillates at 0
More Phase Noise
External Signal at 1
(1 close to 0)
Oscillates at 1
Less Phase Noise
Fabrication
Oscillator layer (oscillates ~10 GHz)Non-overlapping oscillation ranges
Settled on 5-element array instead of 9-element
Injection Locking Setup
Antennas
Oscillators
Clean Source Signal
Phase-shifters
Elements 3,5,7 were injection locked in various combinations
Antenna received array’s combined signal
3 5 7
View from Spectrum Analyzer
Free running at 0
Phase noise appears asnumerous spikes
Injection Locked at 1
Cleaned spectrum byreducing phase noise
Results - Injection Schemes
Phase Noise for Different Injection Schemes (-4 dBm)
-140
-120
-100
-80
-60
-40
-20
0
1.E+03 1.E+04 1.E+05 1.E+06Frequency Offset from Carrier (Hz)
Lf (
dB
c/H
z)
No injection 1-port (middle)2-port (both ends) 3-port (all)Instrumentation noise
Results - Injection Power
Phase Noise at 1 kHz Offset vs. Injection Power
-70
-60
-50
-40
-30
-20
-10
0
1-port 2-port 3-port
Lf (
dB
c/H
z)
-4 dBm Injected 1 dBm Injected
Conclusions
Experimentally verified increasing number of injection ports decreases phase noise Diminishing returns with increase in
portsIncreasing injection power decreases
phase noise Greater effect on phase noise with less
ports