A Low-Power Radar Imaging System

BYDR. GREGORY L. CHARVAT

EM Group

IntroductionThrough lossy dielectric slab imaging has received much attention recently.

Current research is diverse; using various types of frequencies, radar architectures, imaging algorithms, and antenna systems:

MMW radiometers, CW doppler at 900 MHz and 2.4 GHz, pulsed doppler at 5.8 GHz, Noise, stepped frequency CW, UWB impulse at 10 GHz, UWB impulse between 1-3 GHz.

Most of this work has been focused on UWB impulse operating at in the 1-3 GHz band with antennas placed directly up against the slab.

small spatially diverse antenna arrays facilitate the use of various types of beamforming algorithms.

Using specialized beam forming algorithms to minimize Snell’s effects of the slab on the antenna array.

Reasons for this are solid, and have to do with range gating out the ‘flash’ from the slab, and noise power budgeting.

Stepped frequency, FMCW, or CW doppler have been avoided because ‘flash’ from slab limits system dynamic range.

GEOMETRY:

Slab Model EM Properties!r = 5PERMITTIVITY OF THE SLAB

CONDUCTIVITY OF THE SLAB:

LOSSY DIELECTRIC SLAB MODELRANGE PROFILES

•MODELING OF RANGE PROFILES OF A 6 INCH DIAMETER CYLINDER BEHIND A 4 INCH THICK SLAB

•SLAB 20 FT DOWNRANGE•CYLINDER 30 FT DOWNRANGE

LOSSY SLAB

NO SLAB

GEOMETRY

Rail SAR ImagingSmall radar sensor is mounted on a mechanized linear rail

Rail SAR data is acquired using a chirped radar system, which produces data in frequency domain

Range profiles are acquired at evenly spaced increments down the length of the rail

Wide beamwidth antenna is used, so that the radar acquires over-lapping range profiles

Resulting chirped data is saved as a 2D data matrix:

s!xn,!(t)

"

EXAMPLES OF RAIL RAR IMAGINGUSING AN X-BAND FMCW RAIL SAR WITH 5 GHZ OF CHIRP BANDWIDTH

TARGETS LOCATED ON STYROFOAM TABLE

RAIL SAR

SAR IMAGE OF A 5.0 MUSTANG

SAR IMAGE OF GREG’S BIKE

THIS DIRECT CONVERSION FMCW RAIL SAR IMAGING SYSTEM WAS DEVELOPED DURING THE WINTER AND SPRING OF 2006

Through-Slab Imaging Geometry

Rail SAR is located at some stand-off distance form the slab

Slab has lossy dielectric properties

Some target is located behind the slab

Lossy dielectric slab and PEC cylinder model

SLAB AT 20 FT, 6 IN DIAMETER CYLINDER AT 30 FT, CENTERED ON RAIL

Lossy dielectric slab model using wave matrices

! = 0 IN THIS CASE, WILL BE CHANGED TO THE CYLINDER SCATTERING SOLUTION LATER

SLAB 20 FEET DOWNRANGE

Lossy dielectric slab and PEC cylinder model

stargets

!xn,!(t)

"= sscene

!xn,!(t)

"! sback

!xn,!(t)

"

sback

!xn,!(t)

"= dielectric slab model

sscene

!xn,!(t)

"= dielectric slab and cylinder model

SAR IMAGE OF THEORETICAL CYLINDER BEHIND A LOSSY SLAB USING COHERENT BACKGROUND SUBTRACTION:

From modeling to functional radar imaging systems

Development of a high sensitivity range gated FMCW radar architecture to address all design issues observed in simulation.

5 month time-frame (March ’07 to July ’07).

See through slabs at low cost and high performance

Design goal: to graduate

Budget: buried in the noise

Facilities: my basement and garage laboratory in East Lansing

Results:

S-band rail SAR through slab imaging system

X-band rail SAR

S-band Real-time through-slab imaging array

12

Design and Fabrication

1. ACQUIRE OLD JUNK FROM RADIO

SWAP MEET.

2. AFTER SOME WORK IN THE

BASEMENT LAB...

3. COMPLETE RADAR SYSTEM, READ TO

MAKE INTERESTING IMAGERY.

(A 3 STEP PROCESS)

Range gating (pulse width) and approximate receiver sensitivityMDSdBm = !174 + 10 log10 Bn + NF

Bn = 1/T = 25

SENSITIVITY: -96.7 dBm THEORETICAL

MHz Bn = 1/T = 50

SENSITIVITY: -93.7 dBm THEORETICAL

MHz

NF = 3.3 dBASSUME:

High sensitivity range gated FMCW radar architecture

BFO(t) = cos!2!fBFOt

"

LO(t) = cos!2!(2 · 109 + crt)t

"

TX(t) = LO(t) · BFO(t)

TX(t) = cos!2!(2 · 109 + crt)t + 2!fBFOt

"+ cos

!2!(2 · 109 + crt)t! 2!fBFOt

"

RX(t) = cos!2!(2 · 109 + crt)(t! tdelay) + 2!fBFO(t! tdelay)

"

+cos!2!(2 · 109 + crt)(t! tdelay)! 2!fBFO(t! tdelay)

"

High sensitivity range gated FMCW radar

architecture

IF (t) = LO(t) · RX(t)IF (t) =

cos!2!(2 · 109 + crt)(t! tdelay) + 2!fBFO(t! tdelay) + 2!(2 · 109 + crt)t

"

+cos!2!(2 · 109 + crt)(t! tdelay) + 2!fBFO(t! tdelay)! 2!(2 · 109 + crt)t

"

+cos!2!(2 · 109 + crt)(t! tdelay)! 2!fBFO(t! tdelay) + 2!(2 · 109 + crt)t

"

+cos!2!(2 · 109 + crt)(t! tdelay)! 2!fBFO(t! tdelay)! 2!(2 · 109 + crt)t

"

IF (t) =cos

!2!(2 · 109 + crt)(t! tdelay) + 2!fBFO(t! tdelay)! 2!(2 · 109 + crt)t

"

+cos!2!(2 · 109 + crt)(t! tdelay)! 2!fBFO(t! tdelay)! 2!(2 · 109 + crt)t

"

IF PORT ON MXR2 CAN NOT OUTPUT MICROWAVE FREQUENCIES, SO THE HIGH FREQUENCY TERMS DROP OUT:

IF (t) = cos!! 2!(2 · 109 + crt)tdelay + 2!fBFO(t! tdelay)

"

+cos!! 2!(2 · 109 + crt)tdelay ! 2!fBFO(t! tdelay)

"

IF (t) = cos!2!(fBFO ! crtdelay)t

"+ cos

!2!(fBFO + crtdelay)t

"AMP1 IS AN HF AMPLIFIER, SO IT DOES NOT PASS DC, THUS:

High sensitivity range gated FMCW radar

architecture

FIL(t) =!

cos"2!(fBFO ! crtdelay)t

#if !BW

2 + fc < fBFO ! crtdelay < BW2 + fc

0 for all other values

WHICH CAUSES THE OUTPUT OF FL1 TO FILTER OUT ONE OF THE SIDEBANDS FROM THE IF, RESULTING IN:

High sensitivity range gated FMCW radar

architecture

fBFO !BW

2+ fc

THE IF IS FED THROUGH FL1, WHICH IS A HI-Q COMMUNICATIONS FILTER (SUCH AS A CRYSTAL FILTER). OSC1 IS SET TO A FREQUENCY SUCH THAT:

SINCE THIS IS AN FMCW RADAR, AND RANGE TO TARGET IS IN THE FORM OF BEAT FREQUENCY TONES, FL1 EFFECTIVELY BECOMES A HARDWARE RANGE GATE

High sensitivity range gated FMCW radar

architectureTHE OUTPUT OF FL1 IS THEN CONVERTED DOWN TO BASE BAND VIA MXR3 AND OSC1:

V ideo(t) = BFO(t) · FIL(t)

V ideo(t) =!

cos"2!crtdelayt

#if !BW

2 + fc ! fBFO < crtdelay < BW2 + fc ! fBFO

0 for all other values

VIDEO AMP1 IS AN ACTIVE LPF, SO THE HIGH FREQUENCY TERMS DROP OUT, LEAVING A HIGH-Q BAND LIMITED BASE-BAND VIDEO. BAND LIMITING IN FMCW RADAR RESULTS IN RANGE GATING (ONLY LETTING IN A CERTAIN BANDWIDTH OF BEAT TONES):

FRONT END IS FAIRLY ROBUST, LEAVING THE IF TO PREVENT DIGITIZER SATURATION. THIS IS A VERY EFFECTIVE RANGE GATE, AND WILL BE SHOWN IN THE RESULTING IMAGERY.

RANGE GATE IS ADJUSTABLE, SIMPLY INCREASE THE FREQUENCY OF OSC1 TO PUSH RANGE GATE FURTHER DOWN RANGE. CHANGING THE BANDWIDTH OF FL1 CHANGES THE LENGTH OF RANGE GATE

High sensitivity range gated FMCW radar

architectureFURTHERMORE: THE NARROW BAND HI-Q IF FILTER FL1 REDUCES THE EFFECTIVE NOISE BANDWIDTH OF THE RECEIVER, GREATLY INCREASING SENSITIVITY.

fc = 10.7BW = 7.5

A TYPICAL CRYSTAL FILTER HAS THE FOLLOWING SPECS:

MHz

KHz

WHICH WOULD WOULD PROVIDE A THEORETICAL RECEIVER SENSITIVITY OF -131.9 dBm

cr = 800 · 109FOR A CHIRP RATE OF Hz/Sec

THIS WOULD PROVIDE AN EFFECTIVE RANGE GATE OF APPROXIMATELY 9.375 nS

S-Band Rail SARA

A

B

B

C

C

D

D

E

E

1 1

2 2

3 3

4 4

I

BFO output to transmitter

front end

D

Input from BFO CLPR1

Output to radar IF

Input from radar IF

C

B

A

M

IF input from RX front end

Output to radar IF

ATTN1

ATTN2

ATTN3

1

2

3

1

2

3

A

A

B

B

C

C

D

D

E

E

1 1

2 2

3 3

4 4

N

L

J

LO Output to RX Front End

LO Output to TX Front EndRF Input from Yig Oscillator

-3dB

SPLTR1

DELAY1

1 1

2

A

A

B

B

C

C

D

D

E

E

1 1

2 2

3 3

4 4

G F

E

D

C

BA

BFO Input

Out to ATTN3

Input from ATTN2

Out to ATTN2

Video Output Video Output

IF Input

Xtal Filter Mux1

Xtal Filter Mux2

SEL1SEL2

1

FL11

FL13

FL12

FL6

SEL3SEL4

FL7

FL9

FL8

FL10

AMP3

AMP5

1

1

MXR3

CLPR1

VideoAmp1

2

1

34

A

A

B

B

C

C

D

D

E

E

1 1

2 2

3 3

4 4

ML

KK

LO in IF Out

Receive Ant Connection

to Rx in

RX inFL3FL4FL5

FL1MXR2 AMP2

LNA1

ANT2

11

2 2

A

A

B

B

C

C

D

D

E

E

1 1

2 2

3 3

4 4

JI

HH

To TX Out

BFO in LO in

TX Out

-20 dB Out

MXR1 AMP1 FL2

CLPR2

ANT1

1

2

1

23

A

A

B

B

C

C

D

D

E

E

1 1

2 2

3 3

4 4

E

BFO Output

F

N

LO Output to Power Splitter

Video Input to Digitizer

PC

Motor Controller

Ramp

Generator

Yig

Oscillator

PCI6014

NIDAQ Card

1

1

1D Linear Rail

Beat

Frequency

Oscillator

2

PCI Bus

RS232

CTR0 pin

AI0 pin

S-BAND RAIL SARRADAR IN ACTION

FREE-SPACE S-BAND IMAGERY OF 6 INCH RODSLOW POWER IMAGERY: 10 MILI-WATTS TO 5 PICO-WATTS

RODS AT 10 nano-watts

RODS AT 100 pico-watts RODS AT 5 pico-watts

RODS AT 10 mili-wattsRODS IN “S” CONFIGURATION

CLOSE-UP OF RODS

S-BAND RAIL SAR THROUGH SLAB IMAGINGEXPERIMENTAL SETUP

RAIL SAR LOCATED 30 FEET FROM SLAB, TARGETS APPROXIMATELY 10 FEET BEHIND SLAB, TRANSMIT POWER = +10 DBM

S-BAND RAIL SAR THROUGH SLAB IMAGERYMEASURED COMPARED TO THEORETICAL

simulated 6 in cylinder simulated 12 in cylinder

measured 6 in cylinder measured 12 in cylinder

CANS BEHIND CONCRETE12 OZ BEVERAGE CANS BEHIND 4 INCHES OF CONCRETE

6 INCH CYLINDER, ZOOMED OUT THREE 6 INCH TALL, 3/8 INCH RODS

S-BAND RAIL SAR: THROUGH SLAB IMAGERYVARIOUS TARGETS

X-Band front endA

A

B

B

C

C

D

D

E

E

1 1

2 2

3 3

4 4

-20 dB Out

BFO In

Yig Oscillator

LO Input

ThruAttenuator Or

PO

P

PO

O

N

I

M

IF Out

FL14

AMP6

LNA2

ANT4

2

CLPR3

MXR4

CLPR4

MXR5AMP7

ANT3

CIRC1

CIRC2

ATTN4

1

2

3

4 5

1 3

DELAY2

4 5

ATTN5

ATTN6

CIRC3

7.8 -12.8 GHz, plugs directly into existing IF

X-BAND FRONT ENDPLUGS DIRECTLY INTO EXISTING IF, MOUNTS ON EXISTING RAIL SYSTEM

X-BAND IMAGERY COMPARISONFULL POWER AND LOW POWER IMAGERY COMPARED TO DIRECT CONVERSION SYSTEM

pushpins 100 nano-watts

pushpins 10 nano-watts

pushpins 10 milli-watts

DIRECT CONVERSION FMCW VS. HIGH SENSITIVITY1:38 SCALE MODEL F14 MODEL IMAGED USING TWO DIFFERENT RAIL SAR SYSTEMS

F14 model on an direct conversion system F14 model

X-BAND RAIL SAR COMPARISONRANGE GATE IN OPERATION

VERY LITTLE DOWNRANGE CLUTTER NOTICEABLE DOWNRANGE CLUTTER

S-Band Antenna Array8 Receive Elements

44 Evenly Spaced Phase Centers

13 Evenly Spaced Transmit Elements

ANT1 ANT2 ANT3 ANT4 ANT5 ANT6 ANT7 ANT8 ANT9 ANT10 ANT11 ANT12 ANT13

ANT14 ANT15 ANT16 ANT17 ANT18 ANT19 ANT20 ANT21

4.00 20.00 4.0020.004.0020.004.00

5.75

5.75

12.00

2.00

96.00

86.008.00

Copper

Copper

Antenna Feed

FR4 Dielectric

0.14 inch Diameter Mounting Holes

4.00

1.81

1.81

10.0

0

6.38

22.00

LOW-COST LTSA ARRAY ELEMENT

ARRAY IS FUNCTIONALLY EQUIVALENT TO A RAIL SAR OF EQUAL LENGTH

THE S-BAND REAL TIME IMAGING ARRAY ELEMENT LAYOUT

S-Band Antenna Array

A

A

B

B

C

C

D

D

E

E

1 1

2 2

3 3

4 4

32 Bit Hex Code Out to

Array Switch Matrix

E

BFO Output

F

N

LO Output to Power Splitter

Video Input to Digitizer

PC

Ramp

Generator

Yig

Oscillator

PCI6014

NIDAQ Card

1

1

Beat

Frequency

Oscillator

2

PCI-6509

NIDAQ Card3PCI Bus

PCI Bus

CTR0 pin

AI0 pin

32 Lines of DIO

A

A

B

B

C

C

D

D

E

E

1 1

2 2

3 3

4 4

Out to S-band Receiver

Front End RX in Port

K

P2,3

P2,2

P2,1

P2,0

P3,0

P2,7

P2,6

P2,5

P2,4

4

52

3RFout3

RFout4

RFout2

RFout1

RFin

C5

C3

C4

C6

Mini-Circuits

ZX60-

6013E-S+

1

SW7

4

52

3RFout3

RFout4

RFout2

RFout1

RFin

C5

C3

C4

C6

Mini-Circuits

ZX60-

6013E-S+

1

SW6

LNA1LNA2

LNA3LNA4

LNA5LNA6

LNA7LNA8

ANT21 ANT20 ANT19 ANT18 ANT17 ANT16 ANT15 ANT14

RF2 RF1

Com

Mini-Circuits

ZSDR-230

TTL

SW5

1

2

3

4

5

6

7

8

9

1

A

A

B

B

C

C

D

D

E

E

1 1

2 2

3 3

4 4

Input from S-band

Front End TX Out

H

P0,7

P0,6

P0,5

P0,4

-10 dB OutP0,1

P0,3

P0,2

P0,0

P1,3

P1,2

P1,1

P1,0

P1,7

P1,6

P1,5

P1,4

4

52

3RFout3

RFout4

RFout2

RFout1

RFin

C5

C3

C4

C6

Mini-Circuits

ZX60-

6013E-S+

1

SW1

4

52

3RFout3

RFout4

RFout2

RFout1

RFin

C5

C3

C4

C6

Mini-Circuits

ZX60-

6013E-S+

1

SW2

4

52

3RFout3

RFout4

RFout2

RFout1

RFin

C5

C3

C4

C6

Mini-Circuits

ZX60-

6013E-S+

1

SW3

4

52

3RFout3

RFout4

RFout2

RFout1

RFin

C5

C3

C4

C6

Mini-Circuits

ZX60-

6013E-S+

1

SW4

ANT1ANT2ANT3ANT4ANT5ANT6ANT7ANT8ANT9ANT10ANT11ANT12ANT13

CLPR1

1

2

1

2

3

4

5

6

7

8

9

1

2

3

4

5

6

7

IT PLUGS DIRECTLY INTO EXISTING S-BAND RAIL SAR EQUIPMENT

THE S-BAND ANTENNA ARRAYHIGH SPEED ARRAY, CAPABLE OF DISPLAYING 1 SAR IMAGE EVERY 1.9 SECONDS

S-BAND ARRAY FREE-SPACE IMAGERYIMAGERY OF SMALL OBJECTS

6 inch tall rods

3 inch tall nails

2 inch tall nails

1.25 inch tall nails

F14 model, 1:38 scale

S-BAND ARRAY THROUGH-SLAB IMAGERYCOMPARISON OF MEASURED TO THEORETICAL

simulated 6 inch cylinder simulated 12 inch cylinder

measured 6 inch cylinder measured 12 inch cylinder

S-Band Array: Real-Time Imagery of a 6 Inch Cylinder in Free-Space

S-Band Array: Real-Time Imagery of a 12 oz Soda Can in Free-Space

S-Band Array: Real-Time Imagery of a 6 inch Diameter Cylinder Behind a Lossy Slab

S-Band Array: Real-Time Imagery of a 12 oz Soda Can Behind a Lossy Slab

Discussion and Future WorkSummary:

A modified FMCW radar architecture, a hardware range gate without the use of time domain electronic switches or pulsing of IF

Large S-band array for through-slab imaging produced real time SAR imaging through a lossy slab

System operates at stand-off range

Uses an airborne SAR imaging algorithm, producing near real-time imagery of what is behind that slab

Objects as small as coke cans have been tracked in real-time.

Measured data agrees with model.

Future work includes:

A more complex slab model

Using the modified FMCW design for other applications

Increasing array speed, 5-10 frames per second

this can be done by upgrades:

data acquisition

antenna array

IF, increase of bandwidth

Faster YIG, or possibly switch to DDS

For a pdf copy of this slide show please contact: gregory.charvat@ll.mit.edu

EM Group