The French Aerospace Lab HYCAM : A Radar Cross Section Measurement and Analysis System for Time-Varying Targets Yoann Paichard.

The French Aerospace Labwww.onera.fr

HYCAM : A Radar Cross Section Measurement and Analysis System for Time-Varying Targets

HYCAM : A Radar Cross Section Measurement and Analysis System for Time-Varying Targets

Yoann Paichard

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ContentsContents

1. Introduction to Radar Cross Section measurement of time varying targets

2. Overview of the HYCAM system

3. Experimental results

4. Conclusion

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Introduction to the Radar Cross Section

measurement of time varying targets

Introduction to RCS meas. of time varying targets Overview of the HYCAM systemExperimental resultsConclusion

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Radar Cross Section (RCS)Radar Cross Section (RCS)

Introduction to RCS meas. of time varying targets Overview of the HYCAM systemExperimental resultsConclusion

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2

24i

s

R E

E.RlimRCS

unit  : m²

Ei,Hi Es,Hs

turntableNetwork Analyser

Frequency Synthesizer

H

V

H

V

reference channel

test channel

Conventional measurement method (indoor measurements):Emission of several successive frequencies for different angles

RCS depends on :

- Shape and material of the target

- Incident frequency

- Direction of incident and scattered signals

- Polarization

- ...

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Scattering coefficients  : ρ (F, φ, )

Time varying targetsTime varying targets

RCS is time - dependant

Modulation of the emitted signal

t

Target submitted to mechanical or radio-electrical deformations

Example : helicopter blades, jet engines, electronic devices

Introduction to RCS meas. of time varying targets Overview of the HYCAM systemExperimental resultsConclusion

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Measurements constraints Measurements constraints

2.B

cδx

c: wave velocity

x: range resolution

B: frequency bandwidth

The measurement must be performed on a wide frequency bandwidth to obtain a fine range resolution

maxm2.f

1T : highest modulation frequency of the target

maxmf

The measurement time must be short enough so that the target can be considered as stationary

Introduction to RCS meas. of time varying targets Overview of the HYCAM systemExperimental resultsConclusion

= 100 kHzmax

mf T < 5 μs

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Overview of the HYCAM system

Introduction to RCS meas. of time varying targets Overview of the HYCAM systemExperimental resultsConclusion

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Wideband architecture (> 1 GHz) with a high dynamic range (~ 50-60 dB)

Emission and reception of the whole range of frequencies during a time lower

than the stationary time (~ μs)

Real – time computation and display of the RCS (camera mode)

Use of digital technologies

HYCAM (HYperfrequence-CAMera) system featuresHYCAM (HYperfrequence-CAMera) system features

Introduction to RCS meas. of time varying targets Overview of the HYCAM systemExperimental resultsConclusion

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Transmitted waveformTransmitted waveform

Step frequency

Multi-carrier signal

Coded multi-carrier signal (OFDM)

Introduction to RCS meas. of time varying targets Overview of the HYCAM systemExperimental resultsConclusion

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Benefits of a multicarrier signalBenefits of a multicarrier signal

Computation of the scattering coefficients by FFT

Decrease of the cost of the receiver

Possibility of interleaving the test and the reference channel

Resistance against the linearity imperfections of the components

Introduction to RCS meas. of time varying targets Overview of the HYCAM systemExperimental resultsConclusion

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Computation of the scattering coefficientsComputation of the scattering coefficients

Computation of the scattering coefficients on each frequency during a time lower than 5 s

High input data rate : 14.4 GB/s

How to transfert the digitized data to the imaging unit ?

Introduction to RCS meas. of time varying targets Overview of the HYCAM systemExperimental resultsConclusion

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Real-time decimationReal-time decimation

Use of polyphase filters + FFT to process the data

Reduction of the data flow

Holes or " zeros " in the frequency spectrum

Frequencies of interest = carrier frequencies of the scattering coefficient.

Decimation is performed without losing information

Introduction to RCS meas. of time varying targets Overview of the HYCAM systemExperimental resultsConclusion

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Polyphase Filter BankPolyphase Filter Bank

Decimation of the data before the FFT

Polyphase Filter

ADC 2

ADC 1

FFT 2048

CONCATENATION

Polyphase Filter

No computation of the “zeros” Same resolution than a 8192-points FFT in the frequency domain

Introduction to RCS meas. of time varying targets Overview of the HYCAM systemExperimental resultsConclusion

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Hardware implementationHardware implementation

Use commercial IP Cores for the polyphase filters – FFT structure

• Implantation on the FPGA

• Maximal computation power of

640 GMACS [Xilinx, Virtex 5]

Use of the new Vita 41 (VXS) standard for the

data links:

• Max throuhput of 2.5 GB/s

Introduction to RCS meas. of time varying targets Overview of the HYCAM systemExperimental resultsConclusion

Acquisition board :

• 2 ADC 10 bits, 2.2 Gsps• 1 FPGA Virtex 2 Pro -> Evolution towards

Virtex 5

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Experimental results

Introduction to RCS meas. of time varying targets Overview of the HYCAM systemExperimental resultsConclusion

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Frequency bandwidth  : B = 800 MHz

(10.8-11.6 GHz)

HYCAM experimental systemHYCAM experimental system

Range resolution  : x = 19 cm

Emission of a multicarrier signal

Test and reference channels are interleaved

Introduction to RCS meas. of time varying targets Overview of the HYCAM systemExperimental resultsConclusion

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RCS measurement of a time-varying targetRCS measurement of a time-varying target

Modulating signal

Active transponder

VEGA

HYCAM system

VEGA’s receiving antenna

VEGA’s transmitting antenna

Receiving antenna

Transmitting antenna

x0

first echo Active response of the transponder

Introduction to RCS meas. of time varying targets Overview of the HYCAM systemExperimental resultsConclusion

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Extraction of an arbitrary modulation in anechoic chamberExtraction of an arbitrary modulation in anechoic chamber

at x = 0.7 m

Filtering

Modulating signal  : period = 25 s

Sampling time for the modulation  : Te = 1 s

Introduction to RCS meas. of time varying targets Overview of the HYCAM systemExperimental resultsConclusion

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Outdoor measurements on moving targetsOutdoor measurements on moving targets

Frequency shift  : fm = 100 Hz

Range and cross resolutions  : x = y = 19 cm

Doppler resolution  : 5 Hz

dist

ance

Doppler

Introduction to RCS meas. of time varying targets Overview of the HYCAM systemExperimental resultsConclusion

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ConclusionConclusion

An innovative digital system has been designed :• Very short measurement time (a few μs)

• Wideband measurement (several GHz)

• High dynamic range (> 50 dB)

• RCS display in real-time

A new waveform has been used for the measurement and the analysis of the RCS of time-varying targets

• Instantaneous measurement of the scattering coefficients

An experimental system has been built• Extraction of an arbitrary modulation in anechoic chamber

• Implementation of the "microwave camera“ mode (off-line processing)

• Extraction of an electronic modulation on a moving target

Introduction to RCS meas. of time varying targets Overview of the HYCAM systemExperimental resultsConclusion

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PublicationsPublications

Journals• Y. Paichard, J.C. Castelli, P. Dreuillet, G. Bobillot, A. Mérigot, HYCAM : Un Moyen de Mesure et

D’Analyse Fine de la SER des Cibles Scintillantes, in « la revue d’Electricité et d’Electronique (REE) » (in French), janvier 2006.

• Y. Paichard, J.C. Castelli, P. Dreuillet, G. Bobillot, A. Mérigot, "HYCAM : A RCS Measurement and Analysis System for Time-Varying Targets", to be published in IEEE Transaction on Instrumentations and Measurements.

Conference• Y. Paichard, J.C. Castelli, P. Dreuillet, G. Bobillot, "HYCAM: A RCS Measurement and Analysis System

for Time-Varying Targets", IEEE Instrumentation and Measurement Technology Conference, Sorrento, April 2006.

“Giorgio Savastano” award for the best doctoral student paper.

• Y. Paichard, J.C. Castelli, P. Dreuillet, G. Bobillot, A. Mérigot, "First RCS Measurements Results on a Time-Varying Target with a Microwave Digital Camera “HYCAM”", AMTA European Symposium, Munich, May 2006.

Best student paper award in the RCS Measurement session.

Introduction to RCS meas. of time varying targets Overview of the HYCAM systemExperimental resultsConclusion