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

B. Elnour, L. Lo Monte, M. Hurtado, D. Erricolo, A. Nehorai

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

Presented at the 2006 IEEE AP-S International Symposium, USNC/URSI National Radio Science Meeting, AMEREM Meeting July 09-14, Albuquerque, NM, USA

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

Outline

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Motivation Vector Antenna Background Antenna design Goals and assumptions Measurements Conclusion

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

Motivation

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In Radar applications direction of arrival (DOA) of the target echoes is usually estimated using an array antenna. Conventional scalar array antennas measure only one component of the electromagnetic field. A six element vector antenna (SAVA) is an antenna that measures all six components of the electromagnetic field. In a SAVA all available degrees of freedom are exploited, hence all available information of the received signal. 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).

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

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

Antenna Background

Fig 2: Vector antenna by Orbit FR Fig 1: An ideal vector antenna with all six channels [1]

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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]

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

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Antenna Design

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Basic elements: loop and dipole antennas are designed at 2.65 GHz. 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 Employing Co-located Antennas", IEEE Transactions on Microwave Theory and Techniques, vol. 53, pp. 1837 ­ 1844, June 2005

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Design and simulation tool: HFSS 10. Layout tool: Agilent ADS. Results were confirmed with measurements.

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

Loop:

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

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

Loop:

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

Dipole:

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

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

Dipole:

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

Goals and Assumptions

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In this presentation we will demonstrate that using a vector antenna is superior to the use of an array antenna in DOA estimation. 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. 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]. For comparison we computed the Spatial Spectrum of both VA and array antenna. 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. Frequency of operation is 2.65 GHz.

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

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Measurements

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Transmitter : Agilent Signal Generator PSG E8267C-520 RF output bandwidth: 250KHz-20GHz Modulation bandwidth 80MHz Receiver: Agilent Spectrum Analyzer PSA E4440A Frequency bandwidth 3Hz-26.5GHz Digitizer Bandwidth 80HMz

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Antennas: Transmit: Horn Antenna Receive: Vector Antenna and Array antenna Data Processing: PC with Matlab and Visual Basic.

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

Measurements

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

Measurements

Receive Array Antenna: 2-Elements: Loop antennas

Y-axis X-axis X-axis Y-axis

Receive Vector Antenna: Loop and dipole

Z-axis

Lambda/2 Z-axis

Y-axis

Y-axis X-axis X-axis

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

Measurements

Anechoic Chamber: Measurements setup

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

Measurements

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Transmitter and Receiver side of the chamber Other end holds the Object under test. Cylinder.

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

Results:

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]

2D image of the spatial spectrum of vector antenna

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

Results:

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

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

Conclusion

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Measurement results show superiority of using a vector antenna (VA) vs. a scalar array antenna in estimating the direction of arrival. VA fully exploits the polarization information of signal improving the DOA estimation. Further work will be carried in a multi-path environment using different algorithms.

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

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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.

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

Appendix: Coherency Issue

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This system has coherency issue between the signal generator and the signal analyzer, hence the system is incoherent. 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. Coherency has been corrected for the system mathematically using a training signal.

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

Appendix: Coherency Issue

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

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

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