Development of SAR-based UWB
See-Through-Wall Radar
Yunqiang Yang
Song Lin
Alex Zhang
Department of Electrical and
Computer Engineering
University of Tennessee, Knoxville
Outline
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Background Information
Electromagnetic/Antenna Aspects
UWB Components Design/DAQ
Aspects
Imaging Processing Aspects
See-Thru-Wall Experiment
Future Work
See-Thru-Wall Goals
 provide dismounted and remote users
with the capability to detect, locate and
“see” personnel with concealed
weapons/explosives behind obstructions
from a standoff distance
Tactical Operation
 Increased force protection and
survivability of soldier in during operations,
combat search and rescue, and hostage
recovery operations.
 Provide initial information on building
layout and enemy personnel locations
Search Operation
Why Microwave UWB Radar?
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Optical Quality Images at Microwave Frequencies
Active System – Day and Night Imaging
Adverse Weather
Long Stand-off Ability (fine resolution imaging independent
of range)
Both Broad and Spot Coverage
Coherent Imaging
Bi-static and Multi-static Configurations (transmitter
separate from receiver provides stealth)
Penetration of Materials and Particulates (frequency
dependent)
Detection of Ground Moving Target
Microwave Imaging
 Good
scene recognition
Advantages
Day/night,
all weather
Penetration (e.g.
buildings)
 Poor
object recognition
Disadvantages
Non-literal
imagery
Imaging Fundamentals
 Optical
Images
Angle
Angle
vs.
 Microwave
Range
Images
vs. Angle
Range
Angle
Angle
Crossrang
e
Optical Quality at Radar Frequency
Interior Image of Mannequin
Photograph
Mannequin Only
Mannequin Behind Wall
Resolution vs. Frequency
What controls the resolution of these
systems?
 Downrange resolution is solely based on bandwidth in conventional
RADAR (i.e. CW, FMCW)
c
R 
2B
 UWB range resolution is based on the pulse width
 meanwhile cross range timing resolution in a single antenna setup is a
function of the antenna beamwidth (θ), where R is range
Ar  R
 Multiple element or SAR system cross range resolution is a function of
their effective aperture (L) and wavelength (λ)
Ar 
R
L
See-Through Wall Radar Prototype
RF Transceiver
DAC/Control
Image Processing
Wall
Radar Rage: 20 m
Radar PRF: 5 MHz
Pulse Width: 0.5 ns Center Frequency: 10 GHz
Hand-held portable/Ground Vehicle-Based System
Electromagnetic/Antenna Aspects of the
System
 Wave-propagation through the wall, and characterization of
various Walls: Dielectric Constant, conductivity, attenuation Loss
 Efficient EM modeling of scattering from objects inside a room
 Wall parameter effects
 Role of polarization in image enhancement
 Low-profile printed antennas/arrays for the system
UWB Transceiver Design and Data
Acquisition Aspects
 UWB components design: power amplifier,
low noise amplifier, power divider, SP16T switch,
mixer, pulse generator.
 Sampling of UWB signal: equivalent time
sampling technique
Image Processing Issues
 Improve two-dimensional imaging resolution
 Reduce antenna size
 Mitigate the effects of the wall
 Imaging quality depends on:
Bandwidth, Baseline range, Wall distortions,
Wall uniformity, Wall absorption, Positioning
errors
RF Attenuation in Different Wall
Materials
 N.C. Currie, D.D. Ferris, and al, “New law enforcement application
of millimeter wave radar”, SPIE Vol. 3066, pp2-10, 1997
Propagation Modeling
 Frequency domain
measurement
 VNA for insertion transfer
function.
Advanced Design System
(ADS) models
UWB Antenna Consideration
 Wide band-width
 Good impedance match
 Minimum waveform ringing
 Minimum pulse dispersion
 Small size
 Low cost
Types of UWB Antennas
 Tapered slot:
 TEM horn:
 Bow-tie:
Two dimensional microstrip
Most commonly used
Relatively high input impedance
Requires a matching balun
 Resister loaded dipole Low gain and low efficiency
 Discone:
High performance,
Difficult to manufacture 3-D structure
 Bicone:
High performance,
Difficult to manufacture 3-D structure
 Log-periodic:
Dispersive
 Spiral:
Dispersive
Antipodal Vivaldi Antenna
 Developed by Gibson in 1979
 Wide band performance
 Fabricated on dielectric substrates
 Great potential to low cost and weight
 Small size
Tapered flares on different layers
Dimension: 2.15cm x 5.52cm
Substrate: Roger 4003C, 10 mil-thick
Vivaldi Sub-array
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16 Element sub-array
Dim: 18 cm x 40 cm
Wilkinson power divider
Element spacing: 2.15 cm
0
-5
-10
S11 (dB)
-15
-20
-25
-30
-35
-40
-45
4
6
8
10
12
14
f (GHz)
7.5 GHz – 12.5 GHz
16
Pattern: Simulation Versus
Measurement
@ 10 GHz
Measurement: 13dB Gain, 4° Beamwidth
Simulation:
15dB Gain, 3° Beamwidth
Measured Radiation Pattern
E Plane
H Plane
Transmitter/Receiver Structure
1 2 3 4
16
........
Switch
System Block Diagram
UWB See-Through-Wall Imaging Radar
Simulation (in ADS)
UWB_SubHarmonic_Mixer
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Why SubHarmonic_Mixer?
1. Easy to implement in a PCB technology using coplanar
lines.
2. LO frequency can be lowered
3. Provides very high isolation between the RF port , LO
port and IF port. Specially the RF and LO have more than
40 dB isolation in the 8-12 GHz frequency range.
UWB_SubHarmonic_Mixer Simulation
Harmonic Mixer
Frequency Range, RF: 8 - 12GHz
Frequency Range, LO: 8 - 12GHz
Frequency Range, IF: 0.1- 2.5GHz
Conversion loss <13dB
RF to LO isolation > 45dB
RF to IF isolation > 45dB
LO to IF isolation > 45dB
IP3 (Input) 14dBm
LO input power : 7dBm
Parallel-Feedback Dielectric-Resonator
Oscillator
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Why DRO?
DROs are attractive microwave sources because
of their high Q, low phase noise, good output
power and their high stability versus temperature.
They represent a good compromise of costs, size,
and performance compared to alternative signal
sources such as cavity oscillators, microstrip
oscillators or multiplied crystal oscillators.
The parallel-feedback with BJT DRO can achieve
the highest performance in some frequency range.
DRO Simulation
DRO Oscillator
Operating Frequency Range:
9.9-10.1GHz
Phase noise:
-95dBc @ 10KHz
-120dBc @ 1 MHz
Output power:
Temperature stability:
+/- 1MHz
7 dBm
Harmonics:
-40 dBc min
Spurious:
- 80 dBc min
Narrow Band Low Noise Amplifier
Freq range: 9.9-10.1 GHz
Gain:
>11.5 dB
Gain Flatness: +/- 0.5 dB
Noise figure:
1.2 dB
P1dB:
16 dBm
IP3out:
24 dBm
UWB Power Amplifier
Freq range:
2-18 GHz
Gain:
>12
dB
Gain Flatness: +/- 0.5 dB
Psat:
26 dBm
P1dB:
25 dBm
IP3out:
27 dBm
UWB System Topology
SP16T With Antenna Array
SP16T Using SPDT in Series
Hittite SPDT (SMT)
DC - 14.0 GHz
SP4T Measurements
Frequency Range: 7 to 13 GHz
IL: - 4dB with flatness: +/-1dB
Isolation : <- 40dB
Test Fixture Design
Top Side
Bottom Side
RF Layout
Frequency Range: 9 to 13 GHz
IL: - 8dB with flatness: +/-2dB
Isolation : <-45dB
Switching Time: < 50ns
Driver Logic
Pulse Generator
Simulation & Measurement
Results of Pulse Generator
0
dBm(fs(var("TRAN.V!")))
var("TRAN.V!"), V
12
10
8
6
4
2
0
-2
-10
-20
-30
-40
76
77
78
79
80
81
82
time, nsec
83
84
85
86
87
0.0
0.5
1.0
1.5
freq, GHz
2.0
2.5
Pulse Width:
Adjustable 400ps - 1ns
Rise Time: 50ps
Fall Time: 50ps
Bandwidth: up to 2GHz
Solutions for DAQ System
Oscilloscope: for
experimental system
PCI Digitizer: for ground
vehicle based system
UWB Sampler: for handheld portable model
ADC Chip: for handheld portable model
See-Trough-Wall Radar Experiment
Measurements without Wall
Measurements with Drywall
Targets Location
20cm X 24cm
12cm X 24cm
Top View -- Hallway Geometry and UWB
Radar Setup
Concrete Wall
9.30m
Radar
Position
Side Wall
2.85m
Door 1
Door 2
1.02m
Metal-covered Door
Targets
Non-through-Wall Image
Side Wall
Door 2
Gas Tank
Door 1
Cylindrical Target
Image of Water Cup ----- Position 1
Side Wall
Door 2
Door 1
Water Cup
10cm X 12cm
Image of Water Cup ----- Position 2
Side Wall
Door 2
Door 1
Water Cup
10cm X 12cm
CFDTD Simulation
Side View
z
x
120cm
y
Free space gap 6 cm
CFDTD Simulation Parameters
Mesh Size
Nx = 330, Ny = 430, Nz = 330
Cell Size
dx = dy = dz = 1.0cm
Time resolution
dt = 19.15 ps
Drywall boards
thickness = 2cm
Epson=2.4, Sigma=0.003
Local point source
Concrete @ f = 2 GHz
Epson=7.0, Sigma=0.005
240cm
Current simulation Problems
At f=2 GHz =15 cm requiring step size of 1cm.
To increase Mesh Resolution, we needed higher frequency
Operation i.e. more mesh points.
Currently with a 4-processor server it requires 5 hours @ 2 GHz
-at 4 GHz, it is anticipated 5x23 hours !!!
-at 8 GHz it will be 5x26 hours.
Top View
Z = 120 cm
z
16
y
30cm conducting cubic box at
(x=70cm,y=195cm,z=120cm)
x
250cm
16-Element
receiver array
12cm
55cm
Local point
source
30cm conducting cubic box at
(x=145cm,y=355cm,z=120cm)
1
350cm
Radiated UWB Pulse
Baseband signal is Gaussian with 0.8 GHz bandwidth
Carrier is 2 GHz Sine Wave.
Recorded Response at 16 Receivers
Direct Transmission from
source to receivers
Reflection from 1st Target
Reflection from 2nd Target
(m)
Without Gating
Direct Transmission from Source to
Receivers
12 cm: Receiver Spacing
(m)
Direct Coupling Due to the Isotropic Point Source
Reflection from Targets
Reflection from
1st Target
Gating Direct
Transmission
Reflection from
2nd Target
Reflection from
far wall
(m)
After Gating of receivers response due to direct coupling
Extracted I/Q Channel
I Channel
1st Target
Q Channel
(m)
2nd Target
Far wall
Image Recovered from Simulation Data
Future Work
Digital Signal Processing
Comparison of 2-D Spectral Estimation Techniques for
Imaging Synthetic Point Scatterers
Image-Domain TCR is 13 dB
True Points
PML Estimates
Taylor –35 dB n = 5
Sinc
MUSIC
EV
RRMVM
TKARLP (2 quad)
SVA
ASR
TKARLP (all pred)
2 Super SVA, Taylor
2 Super SVA, SVA
MVM
ARLP (2 quad)
Pisarenko
Relative dB scale
Note: S.R. DeGraaf, “SAR Imaging…,”
IEEE T-IP, Vol. 7, No. 5, 1998
–60 dB
0 dB