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A Concept for an Advanced Reflector-Based

Space Surveillance Radar

A. Patyuchenko, M. Younis, G. Krieger, M. Weigel

German Aerospace Center (DLR)

European Space Surveillance Conference07-09 June, 2011

Madrid, Spain

Slide 2

Outline

Introduction

Conventional Radar for Space Debris Detection

Concept of the Reflector-Based DBF Radar System

Aspects of the Improved DBF Radar Performance

Prototype Development

Conclusion


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Slide 3

Outline

Introduction





Conclusion

Slide 4

Space Debris Environment

Space debris orbital man-made space junk is a many-sided problem becoming more

and more critical nowadays.

Low Earth Orbit (LEO)

debris population

SSA has to guarantee the safe and stable space environment.

Reliable and operationally flexible source of information for SSA are required.

Technical requirements for the measurement systems are becoming more stringent.


3/13

Slide 5

Detection of Space Debris

Various ground based radar systems are used to detect space debris at LEO:

Reflector systems are chosen for their high directivity and a low side lobe level.

Classical radar measuring systems have limitations of physical and technical nature.

In particular, reflector systems performance is limited in terms of a mechanical

steering of an antenna and a search volume.

HAX, USMU Radar, Japan

TIRA, Germany

TRADEX, US

Slide 6

Outline

Introduction





Conclusion


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Slide 7

Earth rotation

Operational Modes I

Antenna elevation angle is fixed.

Volume density of space objects is observed

as the Earth rotates.Information on non-cataloged objects is

obtained:

Objects size

Orbit data

Observation methods are translated into two main operational modes:

Beam-Park Mode and Tracking Mode

Beam-Park Mode

Data precision is poor.

Slide 8

Operational Modes II

Antenna pointing direction follows a target.

Target directed observation is performed.

Accurate information on cataloged

objects is obtained:

Tracking Mode

Object characteristics

and orbit data

Initial orbit data are required.


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Slide 9

Elevation view Azimuth view

1c

Lp

1c

Lp

Performance Aspects: Capture Probability

Geometrical representation of the tracking operational mode:

- Cross-Track Orbit Uncertainty

Probability of a target capture depends on the HPBW of the antenna and a slantrange to the target and thus, it is proportional to the observation volume.

Slide 10

Performance Aspects: Antenna Elevation Angle Impact

Peak transmit power = P1

Peak transmit power = P2P1 > P2

Antenna elevation angle [deg.]

Increase of the antenna elevation angle leads to:

- decrease of the beam spatial extension => capture probability decreases;

- decrease of the free space attenuation => detection probability increases.

L-Band

S-Band

X-Band

Ku-Band

Orbit height: 1000 km


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Slide 11

Performance Aspects: Operational Frequency Impact

Capture probability is directly proportional to the HPBW.

Detection probability is directly proportional to the gain.

G2

G1

3dB2

3dB1

G1 < G2

3dB1>3dB2

L-Band

X-Band

03dB

c

Df

2

0

DfG

c

D

- antenna shape and illumination parameter

- antenna diameter

- frequency

- net efficiency

HPBW and gain are inversely dependent in terms of frequency.

Slide 12

Conventional System Performance

3200

Sphere

(10 cm diameter)

30m/L

30m/S

30m/X

Target is orbiting the Erath at 1000 km height.

The slant range of 3200 km is equivalent to the 5 antenna elevation angle for theconsidered system

1/ 42 2

max 3

min(4 )

t

s

G PR

kT L SNR

Maximum detection range:

G

tP

sT

L

- pulse length

- gain

- RCS

- wavelength

- Tx peak power

- loss factor

- system noise temp.

min 11dBSNR

0.99dp

0.01fap

The largest maximum detection range is achieved at X-Band.

Cross-track beam extension at 1000 km distance:

X-Band: 0.96 km, S-Band: 5.3 km, L-Band: 9.38 km.

X-Band system allows the lowest probability of capture.


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Slide 13

Outline

Introduction





Conclusion

Slide 14

Reflector Based DBF Radar Structure

The concept originates from the spaceborne system [1].

Multiple independent digital channels with ADCs.Application of innovative DBF techniques.

Reflector antenna: high directivity and a low side lobe level.

[1] G. Krieger, el al., Advanced concepts for ultra-wide swath SAR imaging, in Proceedings of the 7th European

Conference on Synthetic Aperture Radar (EUSAR 08), Friedrichshafen, Germany, June 2008.

Feed System


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Slide 15

12

1

2

Indicesofthefee

delements

1

2

1

2

Wide Tx low-gain beam illuminates the volume in space.

Narrow Rx high-gain beams follow targets digitally by combining weighted data from

signal channels.

Reflector Based DBF SAR Operation

Slide 16

Outline

Introduction





Conclusion


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Slide 17

Relaxed Requirements for Mechanical Steering

=16

TxRx

16

The corresponding classical radar has a HPBW of 0.36 only and thus needs to be

mechanically steered in the tracking mode.

The DBF system requires no mechanical steering over the angular range of 16(example) and can perform tracking digitally.

L-Band system using 30 m reflector dish and 34 digital channels:

Slide 18

Advanced Operational Modes

Multiple independent digital channels:

Advanced operational modes are possible:

- Track While Scan mode with enhanced efficiency.

- Effective tracking of several targets over a large angular range.

The measurement time can be considerably reduced.

Catalogued and non-catalogued objects: simultaneous capability.


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Slide 19

Improved Capture Probability I

X-Band DBF Radar

30 m

48 channels

Cross-track beam extension at 1000 km is larger by a factor of 45 compared to the

classical X-Band radar.

However the detection probability and thus the maximum detection range is lower

for the DBF Radar due to the decreased gain on transmit.

0.08

3.5

Conventional system

Slide 20

Improved Capture Probability II

The detection probability can be improved by increasing transmit power, using multiple

PAs or by means of sequential switching of channels:

1 2 3

2

1

2

max ( )

t

average

t

P P u t dt

- pulse train waveform( )u t

tavP

receive window

P

1t 2t

P

tmaxP

receive window


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Slide 21

Outline

Introduction





Conclusion

Slide 22


1 personal computer, 2 data storage device, 3 analog-to-digital

converters with an embedded PC, 4 analog signal generator, 5 arbitrary

waveform generator, 6 coupler, 7 reflector antenna.

Multichannel DBF Radar Demonstrator based on the cPCI architecture.

Development and test of the advanced operational modes.


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Slide 23

Outline

Introduction




Conclusion

Slide 24

The new concept allows better performance in terms of a search area and has

relaxed requirements imposed on the mechanical steering of the antenna.

Advanced operational Track While Scan mode with efficient tracking of several

targets simultaneously is possible.

DBF radar system allows high detection probability and large search volume

at higher frequencies.

The prototype system is under development.

The suggested concept has a high operational flexibility and an improved

performance. It opens a wide range of problems which must be further

considered and solved.

Conclusion


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Slide 25

Thank you!

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