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

Fabrication (cont’d)

Transmit layer

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

Acknowledgements

Dr. Jim HarrissXing Wang