Lag Correlator Testing

Aria Meyhoefer

Carnegie Mellon University

Summer 2001

The Lag Correlator

• What it is

• How it works

• What I did with it

– Reflections

– Transmissions

– Signal Response

• Conclusions

17 Unit Lag Correlator

Diode Array

Inductor

Capacitor

Balun

How It Works Antennas read signals off the

sky with path difference depending on source angle

The correlator also allows measurement of the spectrum of any signal detected

Each element of mixer array in the correlator measures the power from a particular direction

Inside correlator delay lines remove signal path delays

Signals travel along paths of equal length to Correlator

Testing the Correlator

• Signal Response Test– Send same signal* into both inputs of correlator– Use different path lengths to create interference– Read response from oscilloscope

• Reflections Test– Send signal* into correlator through directional coupler– Terminate other input and output– Power reflects back though directional coupler to oscilloscope

• Transmissions Test– Send a signal* into one input of correlator– Read signal from other input of correlator– Find attenuation of correlator

* Same microwave signal of 9dBm from 0.01 to 26.5 GHz was always used

Signal Response Results

-30

-20

-10

0

10

20

30

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27

Frequency (GHz)

Voltage (mV)

1 2 3 4 5 6 7 8 9 11 12 14 15 16 Average

• Compared to mixer results

• Expected Response: One part in 158

• Measured Response: One part in 6000

• Correlator is only 2.6% effective

Reflections Results

• Left input reflects 21% of the power• Right input reflects 16% of the power

Transmission Results

• 0.03 mV from right to left

• 0.02 mV from left to right

• Sweep generator outputting 0.4 V

• Average attenuation of about 42 dB

10LOG10

V1

V2

⎛

⎝ ⎜ ⎞

⎠ ⎟ =dB

Summary

• Correlator Response only 2.6%

• Correlator Reflects about 18.5% power

• Attenuation of 42 dB

Thanks

• Jeff Peterson – Carnegie Mellon

• Jeff Rapadas – Device Technologies