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Low-Cost, High Resolution X-Band Laboratory Radar System

For Synthetic Aperture Radar Applications

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EM GroupEM Group

5/6/08

LOW-COST, HIGH RESOLUTION X-BAND

LABORATORY RADAR SYSTEM FOR

SYNTHETIC APERTURE RADAR APPLICATIONS

Electromagnetics Research Group

G.L. Charvat, Michigan State

University



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Motivation and Overview of

Presentation

• Motivation: To self-study SAR imaging technology by developing hardware and algorithmsfor the eventual application of through-lossy dielectric imaging.

• Synthetic Aperture Radar (SAR) Imaging

• Two Small Aperture Linear Rail SAR Imaging Systems

o The Unique Approach to Frequency Modulated Continuous Wave Radar

o The Low-Cost, High Resolution X-band Laboratory Radar System for Synthetic Aperture RadarApplications

• Image formation algorithms developed:o Range stacking, the polar format algorithm (PFA), and the range migration algorithm (RMA)

o Motion compensation (MOCOMP) algorithms, and the map drift (MD) autofocus algorithm

• A theoretical model of a lossy dielectric slab for the characterization of radar systemperformance specifications

o Expected dynamic range of a through lossy dielectric measurement system

• Conclusions and future work



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Synthetic Aperture Radar (SAR)

Imaging

• SAR in general: A radar system traverses a known path acquiring numerous rangeprofiles which are then applied to an image formation algorithm resulting in a highresolution radar image equivalent to a very large real aperture.

• Typical application: Airborne SAR reconnaissance imaging.

• Application discussed in this presentation: small aperture SAR.

Collection geometry.Airborne SAR: most common application

(image from Sandia National

Laboratory, Albuquerque

International Airport at Ku band)

Small aperture rail SAR: typical

application in measuring RCS

of aircraft.



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Principles of FMCW Radar

• Small linear rail SAR systems typically use FMCW, and this is the casefor the research presented in this paper.

• FMCW radar provides range to target information in the form of lowfrequency (near audio) beats.

o This is done by frequency modulating a transmit oscillator, and comparing thecurrent transmitted carrier to the carrier which is reflected from the target

o The closer a target, the lower the beat frequency

o The further a target, the higher the beat frequency



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The MA87127-1 ‘Gunnplexer’ and the

Unique Approach to FMCW Radar

This solution allowed for a very low cost FMCW

Radar design for high volume automotive

applications (pre-UWB).

Center frequency of 10.25 GHz, chirp BW of 70

MHz, transmit power 10 dBm, front end NF

= 10 dB



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5/6/08

The Unique Approach to FMCW

Radar



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5/6/08

The Unique Approach to FMCW:

Range Profile Results

30 dBsm trihedral corner reflector at 25 ft 30 dBsm trihedral corner reflector at 40 ft



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EM GroupEM Group

5/6/08

The Unique Approach to FMCW:

Data Collection Geometry



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5/6/08

Image Formation Algorithms

A range stacking algorithm. In this

experiment a 20 dBsm trihedral

corner reflector was placed 25 ft

down range from the rail, and a 30

dBsm trihedral corner reflector was

placed 40 ft downrange.

The PFA with narrow beamwidth and

narrow bandwidth assumptions. A

target scene was setup with a 20

dBsm trihedral corner reflector

located 25 ft downrange, and a 30

dBsm trihedral corner reflector

located 65 ft downrange.



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5/6/08

Image Formation Algorithms

Target scene: 20 dBsm trihedral corner reflector located 25 ft downrange, and a 30 dBsm trihedral

corner reflector located 65 ft downrange.

PFA:

RMA:



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5/6/08

The Low-Cost, High Resolution, X-Band

Laboratory Radar System for SAR Applications

Specifications:

TX: 15 dBm

RX dynamic range 60 db

Chirp: 8 GHz to 12.4 GHz



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5/6/08

The Low-Cost, High Resolution, X-Band

Laboratory Radar System for SAR Applications

Range Profile Data

Seven 0 dBsm cylinders

spaced ever 1 ft

Seven 0 dBsm cylinders

spaced ever 2 ftTarget scene in

February…

Only 2.4 GHz of chirp bandwidth used here:



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5/6/08

The Low-Cost, High Resolution, X-Band Laboratory

Radar System: Rail SAR Implementation (the $240

Genie garage door opener based rail SAR)



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5/6/08

Additional SAR Image Improvement

Algorithms

• Motion Compensation Algorithms (MOCOMP),

developed for data simulation only.

Downrange and cross range motion error

compensation developed.

Simulations conducted to determine mechanical

tolerances of the linear rail.

80 mils max downrange error.

• Map Drift (MD) autofocus algorithm



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5/6/08

SAR Imagery of Pushpins and

4.37mm Spheres

pushpin

row of 4.37mm

diameter spheres



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5/6/08

SAR Imagery of Model Airplanes

1:72 scale

model B52

1:48 TR1

1:32 F14

Model

airplane

airfield



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5/6/08

SAR Imagery of Unusual Objects

Greg’s bike on radar.



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A Theoretical Model of a Lossy Dielectric Slab for

the Characterization of Radar System

Performance Specifications

A ‘broad side of the barn’ scenario

The ultimate small aperture

SAR application: try to

image a target on the other

side of a lossy dielectric.

We first must examine the

‘broad side of the barn’

scenario to determine the

minimum system

performance specifications.



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5/6/08

Solving the Problem

Vector Magnetic Potential Solution:

)(4

),( 0

)2(

00 zkHj

IzyAx

!

µ= !

"

"#

+##

+

#+ y

yjktzjp

dkeY

Y

p

e

j

Iy

1

1

4

)2(

0

$

µ

Problem solved by spatial frequency

transforms, matching spatial frequency

boundary conditions on 5 layers, resulting in

7 equations and 7 unknowns, which were

solved for the fields directly next to the line

source.

Many tedious steps later……



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Theoretical Data

t = -5 feet

b = -5.3048 feet

d = -10 feet

observation point = {y = 0.1 feet, z = 0.1 feet}

The frequency sweep for the time

harmonic results was from 250

MHz to 3 GHz.

Logarithmic range profile Real valued range profile



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Minimum Dynamic Range

Requirements Determined

• Dynamic range requirements for a radar or S11 network analyzer were

determined using this model, it was found that a minimum of 28 dB of

dynamic range is required to detect ‘the broad side of a barn.’

• These results are driving the architecture of the radar system currently

under development (it is not homodyne FMCW with only 60 dB of

dynamic range as shown earlier).

• Future work on this theoretical model will include using targets other

than an infinite PEC plane, more complicated lossy dielectric models,

and more sophisticated source models.



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Conclusions and Future Work

• Two rail SAR imaging systems were developed.

• Four imaging algorithms were developed.

• Image improvement algorithms were developed.

• High resolution SAR imagery was created.

• A theoretical model of a lossy dielectric slab was developed todetermine through lossy dielectric radar system performancespecifications.

• Future work will include more complicated lossy dielectricmodels with different targets and more complicated lossydielectric models.

• Future work with through-lossy dielectric imaging will includethe development of a through lossy dielectric radar imagingsystem utilizing all knowledge gained from previous researchon radar imaging.

• For more information, please visit www.msu.edu/~charvatg

em group electromagnetics research groupglcharvat.com/website pdfs/charvat_phd_seminar.pdf ·...

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