Experiments to measure the direction of arrival (DOA ...nehorai/MURI/publications/APSIS06_Elnour.pdfElnour, Lo Monte, Hurtado, Erricolo, Nehorai–Experiments to measure the direction

Department of ECE, University of Illinois at ChicagoChicago, IL 60607 USA

Presented at the

2006 IEEE AP-S International Symposium, USNC/URSINational Radio Science Meeting, AMEREM Meeting

July 09-14, Albuquerque, NM, USA

supported by NRL/DARPA Grant #N00173-06-1-G006

Experiments to measure the direction of arrival (DOA) using a Vector Antenna

B. Elnour, L. Lo Monte, M. Hurtado,

D. Erricolo, A. Nehorai

Elnour, Lo Monte, Hurtado, Erricolo, Nehorai– Experiments to measure the direction of arrival (DOA) using a Ve ctor Antenna

Outline

§ Motivation

§ Vector Antenna Background

§ Antenna design

§ Goals and assumptions

§ Measurements

§ Conclusion


Motivationn In Radar applications direction of arrival (DOA) of the target echoes

is usually estimated using an array antenna.

n Conventional scalar array antennas measure only one component ofthe electromagnetic field.

n A six element vector antenna (SAVA) is an antenna that measuresall six components of the electromagnetic field.

n In a SAVA all available degrees of freedom are exploited, hence all available information of the received signal.

n Demonstrated by theoretical results of:Nehorai and Paldi (A. Nehorai and E. Paldi, “Vector-sensor array processing for electromagnetic source localization”, IEEE Trans. Signal Process., Vol. 42(2), Feb. 1994, pp.376-398).

vector antenna should outperform the scalar array antenna, in the accuracy of DOA estimation.


Antenna Background

Fig 1: An ideal vector antenna with all six channels [1]

Fig 2: Vector antenna by Orbit FR

§ There has been few attempts to design a six element vector antenna.

§ Orbit FR (Flam & Russell Inc.) designed a six element VA at 30MHz to 75MHz, with poor isolation between elements.[2]


Antenna Designn Basic elements: loop and dipole antennas are designed at 2.65

GHz.

n Loop and dipole design is based on the design of a three element Vector (2.25 GHz) Antenna by:A. Konanur, K. Gosalia, S. Krishnamurthy, B. Hughes, and G. Lazzi,“Increasing Wireless Channel Capacity Through MIMO Systems EmployingCo-located Antennas”, IEEE Transactions on Microwave Theory and Techniques, vol. 53, pp. 1837 – 1844, June 2005

n Design and simulation tool: HFSS 10.

n Layout tool: Agilent ADS.

n Results were confirmed with measurements.


Loop:

n Substrate Material: Rogers 4003, er=3.38, H=1.5mmn Board dimensions = 90mm x 90mmn Optimized radius of loop = 30.5mm, 2mm wide traces.n Bottom Ground Patch = 22mm x 22mm, Top Ground Arms= 4mm wide


Loop:


Dipole:

n Substrate Material: Rogers 4003, er=3.38, H=1.5mmn Board dimensions = 41mm x 10mmn Optimized total length of dipole = 41mm, 0.5mm wide traces.


Dipole:


Goals and Assumptions

n In this presentation we will demonstrate that using a vector antenna is superior to the use of an array antenna in DOA estimation.

n A six element Vector antenna will be simulated with the use of a loop antenna and dipole antenna in all three axes for each element, to demonstrate proof of concept with measurements.

n The DOA of the target echo is computed using MUSIC (Multiple Signal Classification) algorithm. When implementing the algorithm, we have assumed no cross coupling between antenna elements and ideal antenna patterns [3].

n For comparison we computed the Spatial Spectrum of both VA and array antenna.

n Object: Cylinder of copper; L=61cm, D=10.5cm. Placed vertically along z-axis, with zero azimuth and zero elevation angles with respect to Transmitter and receiver antennas.

n Frequency of operation is 2.65 GHz.


Measurementsn Transmitter :

Agilent Signal Generator PSG E8267C-520RF output bandwidth: 250KHz-20GHz Modulation bandwidth 80MHz

n Receiver: Agilent Spectrum Analyzer PSA E4440AFrequency bandwidth 3Hz-26.5GHzDigitizer Bandwidth 80HMz

n Antennas:Transmit: Horn AntennaReceive: Vector Antenna and Array antenna

n Data Processing:PC with Matlab and Visual Basic.


Measurements


Measurements

Lambda/2

Receive Array Antenna:

2-Elements: Loop antennas

Receive Vector Antenna:

Loop and dipoleZ-axis

Y-axis

Z-axis

X-axis

Y-axis

X-axis

Y-axis

X-axis

Y-axis

X-axis


Measurements

Anechoic Chamber: Measurements setup


Measurements

n Transmitter and Receiver side of the chamber

n Other end holds the Object under test. Cylinder.


Results:

2D image of the spatial spectrum of vector antenna

Spatial spectrum is not a true spectrum in any sense.It is a measure, used in digital signal processing to exhibit peaks in the vicinity of the true DOA. [4]


Results:

1D plot of the spatial spectrum of vector antenna vs. scalar array


Conclusion

n Measurement results show superiority of using a vector antenna (VA) vs. a scalar array antenna in estimating the direction of arrival.

n VA fully exploits the polarization information of signal improving the DOA estimation.

n Further work will be carried in a multi-path environment using different algorithms.


References

[1] M.R. Andrews,P.P Mitra,and R. DeCarvalho, “Tripling the capacity of wireless communications using electromagnetic polarisation,” Nature, vol. 409, 18 Jan. 2001

[2] “Performance analysis of the superCART antenna array” , MIT Lincoln Lab., Lexington,MA, Project Rep. AST-22, Mar. 1992.

[3] P. Stoica and A. Nehorai, "Performance comparison of sub space rotation and MUSIC methods for direction estimation," IEEE Trans. on Signal Processing, Vol. ASSP-39, pp. 446-453, Feb. 1991.

[4] H. Krim and M. Viberg, "Two decades of array signal processing research," IEEE Signal Processing Magazine, vol. 13, pp. 67-94, Jul. 1996.


Appendix: Coherency Issue

n This system has coherency issue between the signal generator and the signal analyzer, hence the system is incoherent.

n Coherency issue is due to the fact that transmitter and the receiver are not using the same local oscillator hence a phase difference between them.

n Coherency has been corrected for the system mathematically using a training signal.


Appendix: Coherency Issue

I-Q training pulse added to the original waveform. It is used to calculate phase incoherency in the received signal.

Documents

Experiments to measure the direction of arrival (DOA ...nehorai/MURI/publications/APSIS06_Elnour.pdfElnour, Lo Monte, Hurtado, Erricolo, Nehorai–Experiments to measure the direction