Development and Operation of a Noise-Correlation Based Antenna Measurement System

1. Development and Operation of a Noise-Correlation Based Antenna Measurement System A Thesis by David A. Dieter Under the Supervision of Eric K. Walton and Advisement of Walter D. Burnside

2. February 23, 1978 Born: East Cleveland, Ohio. 1996 Diploma: Solon High School, Solon Ohio Graduation with Honors 1996 Begin Undergraduate Work: The Ohio State University 1998 - 99 Co-op: Ericsson, Research Triangle Park, North Carolina 1999 Begin Research at the Electroscience Lab 2001 Bachelor Degree: The Ohio State University with Honors and Distinction 2002 Masters Degree: The Ohio State University [expected] VITA

3. Defense Presentation Overview • Introduction • System Theory • Performance Issues • Implementation • Experimentation • Measurement Setup and Results • Conclusion • QUESTIONS??

4. Introduction • Noise Correlation Antenna Measurement System (NCAMS) • Project Goal • Key Step = Derivation of the Impulse Response • Measure Success = Network Analyzer Data Comparisons • Final Experimental Goal

5. Theoretical Approach • * Use Noise Correlation, Find the System Impulse Response * • Transform Time-Domain Response into Frequency-Domain Response • Normalize System Response with AUT to System Response with Standard-Gain Antenna

6. TX hRX(t) N(t) NOISE N(t) RX N(t-) Entire System Impulse Response = h(t) R(t) LPF y() Noise Correlation Device (NCD)

7. Impulse Response Explanation A1 cos(1*t+1) A cos(1*t) A cos(2*t) A2 cos(2*t+2) System A3 cos(3*t+3) A cos(3*t) A cos(*t) A4 cos(*t+)

8. NCD Derivation of Impulse Response N(t)  h(t) h()  RNN() N(t) h(t) Cross Correlation N(t - ) Delay =  …where RNN(t) is the autocorrelation of the noise

9. Frequency Domain Translation Fourier Transform = F { h(t)  RNN (t) } = H(f)  PSD(f) = H'(f) = Bandlimited Frequency Response

10. Normalizing Data Recall that h(t) is really a combination of many impulse responses h(t) = hrx(t)  htx(t)  hcable(t)  hsystem(t) H'(f) = H'rx(f)  H'tx(f)  H'cable(f)  H'system(f)

11. Normalizing Data (cont'd) So if we perform the same measurement twice with different receive antennas... H1'(f) H'AUT(f)H'tx(f)H'cable(f)H'system(f) H2'(f) H'stan(f)H'tx(f)H'cable(f)H'system(f) H'AUT_relative(f) = H'AUT(f) / H'stan(f) H'AUT_absolute(f) = H'AUT_relative(f)  H'stan(f) = H'AUT(f) =

12. Theory Conclusions • Noise correlation can determine the frequency response of an AUT normalized to a standard antenna • The final normalized term is independent of the system response • SO... we can use another measurement system to verify the NCAMS results

13. Performance Issues • SNRo is same for any such device • UWB noise systems are not susceptible to common interference problems • Interfering energy is divided by Processing Gain Gmax = B / fc

14. Implementation • Hardware = Ex-Noise Radar • Performs Correlation as Explained • Uses External and Variable Delay • Operates 1.0 - 2.0GHz w/ fc = 10Hz • Processing Gain = 80dB • A/D Converter for Data Acquisition and Variable Delay Control • RS-232 Serial Communication Port

15. Serially Controlled Variable Delay • Can be adjusted in 12ps to any arbitrary delay value from: 0.0 to 31.75ns in 0.25ns steps 1 / 0.25ns = 4.0GHz = 2  2.0GHz Nyquist Theory Satisfied

16. Comments on Delay • NCD can record an impulse response as long as all transients die within the 32ns variable delay window. • Fixed delay coils are added in series with variable, to move impulse response into that window. • Due to variable delay step, response must be bandlimited to 2.0GHz

17. Sample Impulse Waveform from NCD V 0.0ns 31.75ns nT (n * .025)

18. Software • Main Design Portion of Thesis • Requirements • All Signal Processing Done in One Package • Provide Immediate Frequency-Domain Results • Save, Plot, Recall, Print Options • Intuitive / User Friendly • Portable • Labview (National Instruments)

20. Data Acquisition Process

21. Notable Program Items • Simultaneous Display of up to three data scans to show repeatability • Option of AUT, CAL, or AUT/CAL data display with one click • "Save" option produces spreadsheet of data readable by Excel or Lotus • Can be compiled to PC executable

22. Experimentation • Three experiments performed to verify NCAMS data against Network Analyzer data • Preliminary: Four antennas tested before software was developed • Secondary: Approximation to Final Measurement • Final: Azimuth Pattern of Auto-Antenna

23. Spectral Characteristics of NCD

24. Preliminary Experiment Setup

25. Preliminary Results

26. Preliminary Results (cont'd)

27. Secondary Experiment • Build a model of antenna to be used on car in final experiment • Test it under same conditions as final measurement without the rotating car • Measure phase and magnitude and compare, again, to Network Analyzer

28. Car-Antenna Design Scheme • Use tuning stub to set resonance

29. Secondary Experiment Setup

30. Secondary Experimental Results

31. Final Experiment • Build loop antenna on car • Rotate car and record data in 10 degree increments • Plot gain pattern at antenna operating frequency • Compare NCAMS and Network Analyzer data

32. Final Experimental Setup

33. Final Normalized Results

34. Final Absolute Results

35. Conclusion • Noise Correlation can be used to measure complex frequency response of an AUT within decibels of the same network analyzer results • It's suitable for outdoor measurements • The usability of results may decrease as bandwidth of AUT decreases • Dispersive Antennas?