RFMTC11GÄVLE OCTOBER 4–5th 2011

Industrial radar sensor arrays and their applications

October 04, 2011

P. Vainikainen, V. Mikhnev, Ye. Maksimovitch, M.-K. OlkkonenAalto University School of Electrical Engineering

SMARAD Dept. of Radio Science and EngineeringP.O. Box 13000, FI-00076 AALTO Finland

valeri.mikhnev@aalto.fi

Outline

• Wideband technologies• UWB antennas and antenna arrays• Signal processing techniques• Experimental examples• Summary

2011-10-04

Wideband technologies• Impulse technology

– georadar– subsurface radar– level gauges

• Frequency-swept sine-wave technology– moisture sensors– level gauges– thickness gauges– sensors for material characterization– anti-collision radar

• M-sequence technology– attempts to combine advantages of the both technologies above– very high speed of data acquisition

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Tapered-slot UWB antenna

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Antenna width 120 mmAntenna length 230 mm

Substrate FR-4R-cards 200 Ω/

Elliptical form of flares

Width of microstrip 1.8 mm stub length 10 mm

Slotline width 0.5 mmstub length 13 mm

The both stubs are circular 85º sectors.

R-cards

Tapered-slot UWB antenna

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-150 -100 -50 0 50 100 150

-40

-30

-20

-10

0

10

solid flares

corrugated edges

corrugated edges and R-cards

Angle, [deg]

Ga

in, d

B

E-plane

Unloaded antenna

Loaded antenna

E-field

Tapered-slot UWB antenna

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0 1 2 3 4 5 6 7 Frequency [GHz]

-10

-5

0

5

10

15

Gai

n V

SW

R

wsvr 0

5

10

15

UWB antenna arrays

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direction of scan

transmitting antenna

receiving antenna

Double-ladder Zigzag array array

3 cm

UWB antenna arrays

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H–V V–H

V–V H–H

G. Alli et al, “Data processing for mine-detection polarimetric ground penetrating radar array,” in Proc. of the 10th Int. Conf. on Ground Penetrating Radar, 2004, Delft, 4p.

Signal processing

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Two subtasks of interest:•Detection of reflecting targets by the sensor•Evaluation of parameters of the target and its discrimination

Signal component

...........................

Time-frequency analysis

Natural complex resonances

Wigner-Ville transform

Evaluation and discrimination

Set of features

Signal processingfor the case of GPR

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Extraction of amplitude vs time

Extraction of phase vs time

Removal of the phase due propagation

Intensity of pixel

Color of pixel

B-SCAN

Phase profile retrieval

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1. Determination of dominant peak by magnitude in every A-scan and its filtering by the one-dimensional Gaussian filter yielding partial range profile by amplitude.

2. Derivation of the phase profile corresponding to the peak using

where L is position of the peak.

3. Calculation of the residual of the signal after subtracting the filtered dominant peak.

4. Return to the step 1 until given number of peaks is reached or all peaks above given threshold are processed.

5. Summing up obtained profiles. Derivation of both amplitude and phase versus time.

cLtffitXanglet 2exp 21

Building GPR image

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90

180 0

270

B-scan in phase

Image

B-scan in amplitude Threshold

Final image

Color map

Experimental results

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Experimental setup:

• Network analyzer Agilent E5071B

• Frequency range 1.3 – 6.5 GHz

• Tapered-slot antennas

T-R antenna pair

Network analyzer

Conventional grayscale image Pure phase image Amplitude-phase image

Metal rods

In sand

Experimental results

2011-10-04Distance along track [cm]

De

pth

[cm

]

0 10 20 30 40 50

0

10

20

30

40

Distance along track [cm]

De

pth

[cm

]

10 20 30 40 50

0

10

20

30

40

Void in sand PMN mine simulant in sand

Metal rod (orthogonal polarization) Plastic pipe (parallel polarization)

Summary• A modified UWB tapered-slot antenna exhibiting high wideband

gain and low level of sidelobes has been developed.

• A novel microwave imaging method based on separate determination and representation of amplitude and phase profiles has been proposed.

• Subsurface objects can be detected by amplitude and discriminated by phase in a common color image.

• The retrieval of the phase profile can be applied to other tasks of microwave sensing. So, air gaps between shotcrete and rocks in tunnels can be detected and recognized by this method.

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