THE CITADEL, THE MILITARY COLLEGE OF SOUTH CAROLINA
171 Moultrie Street, Charleston, SC 29409
Maximizing Harmonic-Radar Target Response:
Duty Cycle vs. Peak Power
Anthony F. Martone, Kelly D. Sherbondy
U.S. Army Research Laboratory
Adelphi, MD 20783
Kyle A. Gallagher, Ram M. Narayanan
Pennsylvania State University
University Park, PA 16802
Gregory J. Mazzaro
The Citadel, The Military College of South Carolina
Charleston, SC 29409
02-Apr-2016
2
Presentation Overview
• Introduction to Nonlinear Radar
• Concept, Motivations
• RF Nonlinearity, Sources, Harmonics
• Harmonic Stepped-Frequency Radar Research
• Harmonic Radar, for Detecting RF Devices
• Stepped-Frequency, for Ranging
• Harmonic SFR Experiments
• Latest Results & Future Work
U.S. Army Research Laboratory
Synchronous Impulse Reconstruction Radar
3
Nonlinear Radar Concept
Applications:
Advantages:
Disadvantages:
Target presence/location
is indicated by receiving
frequencies that were
not transmitted.
Tx
Rx
• locate personal electronics during emergencies
• detect electronically-triggered devices
electronic
target
• It is easier to separate targets from clutter because most clutter is linear.
• Targets require high incident power to drive them into non-linear behavior.
• Received responses are usually very weak compared to the transmitted “probe” signals.
4
Sources of Nonlinearity
+
_ +
_
Active elements & components – by design; above system noise floor
Passive elements & components – unintended; below system noise floor
diodes transistors amplifiers mixers
f1
f2
f1 + f2
contacts [1,2]
metal 1
metal 2
oxide
metal
thermal
effects [5] connectors [3]
V R
ferro-electrics [4]
Nearly all electronics are nonlinear, to some degree.
5
Temperature-Dependent
Resistance
Vin R
Iout
voltage applied,
current flows
resistor
heats up
resistance
increases current
decreases
resistor cools
down resistance
decreases
current
increases
input: constant
output: sinusoidal
nonlinear
Vin
time
Iout R
time time
Tx
Rx
6
Nonlinear Radar Research
We view each target as
a collection of RF
nonlinearities.
Ein
Erefl... LNA
BPF
one possible
signal path:
7
Nonlinear Radar Research
Tx
Rx
• Which frequencies and waveforms are best to transmit?
• What is the minimum transmit power required for detection?
• Which is the best antenna design (gain, polarization, etc.) for detection and ranging?
• How should the transmitter be designed to achieve high linearity?
• How should the receiver be designed to achieve high sensitivity?
• How should a signal processor be designed to recognize familiar targets?
This type of
radar research
is in its infancy.
8
Harmonic Radar Theory
2 3
o u t 1 in 2 in 3 in. . .E a E a E a E
Let the nonlinearity
be approximated by
a power series [6]
Let the input waveform be a sinusoid: in 0 0cosE E t
Then the device response (output) is
2 3
o u t 1 0 0 2 0 0 3 0 0co s co s co s ...E a E t a E t a E t
2 3
2 0 3 0
o u t 1 0 0 0 0 0c o s 1 c o s 2 3 c o s c o s 3 ...
2 4
a E a EE a E t t t t
origin of harmonics
input
output
from [7]
9
Harmonic Radar Theory:
Time Domain
in 0 0 0
0
0
co s 1 V
1 M H z2
V V t V
f
Let the input be a single tone,
at 1 MHz with amplitude = 1 V:
In the time domain, nonlinearity
manifests itself as waveform distortion
(e.g. rectification, saturation).
2
o u t 1 0 0 2 0 0
3 4
3 0 0 4 0 0
5 6
5 0 0 6 0 0
c o s c o s 2
c o s 3 c o s 4
c o s 5 c o s 6 ...
V V t V t
V t V t
V t V t
The output is a sum of sinusoids
at 1 MHz, 2 MHz, 3 MHz, etc:
input
output
10
input = { f }
output = { f, 2f, 3f, 4f, 5f, 6f, … }
Harmonic Radar Theory:
Frequency Domain
In the frequency domain, nonlinearity
manifests itself as spurious spectral content
(e.g. harmonics, intermodulation).
in 0 0 0
0
0
co s 1 V
1 M H z2
V V t V
f
Let the input be a single tone,
at 1 MHz with amplitude = 1 V:
2
o u t 1 0 0 2 0 0
3 4
3 0 0 4 0 0
5 6
5 0 0 6 0 0
c o s c o s 2
c o s 3 c o s 4
c o s 5 c o s 6 ...
V V t V t
V t V t
V t V t
The output is a sum of sinusoids
at 1 MHz, 2 MHz, 3 MHz, etc:
input
output
11
Prior (Published) Work
[9]
[8]
RADAR TAGS for INSECT TRACKING
[10]
• simulations show detection possible > 22 m at 80 GHz
AUTOMOTIVE RADAR for detecting
“VULNERABLE ROAD USERS”
MILITARY RADAR for detecting
MANMADE METALLIC OBJECTS
[11]
NLR for detecting
RF devices is novel.
12
Presentation Overview
• Introduction to Nonlinear Radar
• Concept, Motivations
• RF Nonlinearity, Sources, Harmonics
• Harmonic Stepped-Frequency Radar Research
• Harmonic Radar, for Detecting RF Devices
• Stepped-Frequency, for Ranging
• Harmonic SFR Experiments
• Latest Results & Future Work
U.S. Army Research Laboratory
Synchronous Impulse Reconstruction Radar
13
1-Tone Continuous-Wave
Experiment
step
attenuator
Ptrans
targ
et
antenna
Prec
Tektronix AWG7052
arbitrary waveform generator Amplifier Research
50-W 1-GHz RF amplifier
Rohde & Schwarz FSP
40-GHz spectrum analyzer
Gigahertz Transverse
Electromagnetic cell
We performed harmonic experiments
wirelessly, at high power, in a controlled environment.
14
GTEM cell, outside, front GTEM cell, outside, back
Gigahertz Transverse
Electromagnetic cell
VTx
1-Tone Continuous-Wave
Experiment
pictures from [7]
A GTEM cell is essentially
a large, flared waveguide.
15
target placement GTEM cell, inside
antenna, absorber
VTx
VTx
1-Tone Continuous-Wave
Experiment
A GTEM cell is essentially
a large, flared waveguide. Gigahertz Transverse
Electromagnetic cell
16
1-Tone Continuous-Wave
Measurements
We found that many commercially-available RF devices
respond harmonically to incident continuous waves.
GTEM cell
Ranging of targets is not possible
using continuous waves.
17
PreflAgilent
E4411B
MiniCircuits
ZFDC-20-4
RG-58 SMA cable, 1 ft
coupled
out intarget
RG-58 BNC
cable, 3 ft
HP 33120A
Ptrans
f0
Mf0
f0
Mf0
(–20 dB)
1-Tone Pulsed
Experiment
f0 f0
… …
Transmitted
waveform:
Ptrans = 400 mW (fixed)
DcPpeak = Ptrans
“target” vary duty cycle Dc
18
a v g ,d B
re fl 0
1 0
to ta l,d B
in c
1 0
1 0 lo g
1 0 2 lo g
M
c
P M f
M P
M D
For a fixed transmit power, it is advantageous to
reduce the duty cycle to generate a stronger nonlinear
reflection from the target, at any particular harmonic.
1-Tone Pulsed
Measurements
Prefl
“target”
Transmitted
waveform:
f0 f0 … …
19
A1
f1
A2
f2
A3
f3
A4
f4
A5
f5
f0 f0 + Df f0 + 2Df f0 + 3Df f0 + 4Df
amplitude
phase
frequency
…
…
…
…
Tra
nsm
itte
d
Rec
eived
P
roce
ssed
IDFT
2
cR t
Linear
Stepped-Frequency Radar
After constructing H() of the
environment, an inverse DFT
provides range (distance-to-target).
20
Nonlinear
Stepped-Frequency Radar
A1
f1
A2
f2
A3
f3
A4
f4
A5
f5
2f0 2f0 + 2Df 2f0 + 4Df 2f0 + 6Df 2f0 + 8Df
amplitude
phase
frequency
…
…
…
…
IDFT
2
cR t
Tra
nsm
itte
d
Rec
eived
P
roce
ssed
After constructing H() of the
environment, an inverse DFT
provides range (distance-to-target).
21
12 ft
quad-ridge
horn antenna
target location
( all targets were place
with antennas oriented
vertically )
We set up our antenna and targets in a low-metal-content
environment at ARL’s Adelphi Laboratory Center.
Nonlinear SFR:
Over-the-Air Experiment
22
arbitrary
waveform
generator
20GS/s
oscilloscope
power
amplifier
to scope
from power
amplifier
to scope
to/from
antenna directional
coupler
low-noise
amps x3 diplexers
x2
Most of the prototype radar hardware
pieces were commercial off-the-
shelf components or standard radio-
frequency laboratory instruments.
Data capture and processing were
performed on a laptop, in Matlab.
Nonlinear SFR:
Over-the-Air Experiment
23
Presentation Overview
• Introduction to Nonlinear Radar
• Concept, Motivations
• RF Nonlinearity, Sources, Harmonics
• Harmonic Stepped-Frequency Radar Research
• Harmonic Radar, for Detecting RF Devices
• Stepped-Frequency, for Ranging
• Harmonic SFR Experiments
• Latest Results & Future Work
U.S. Army Research Laboratory
Synchronous Impulse Reconstruction Radar
24
Nonlinear Step-Freq Radar:
Latest Results
Both targets were detected,
individually and simultaneously,
up to a distance of 7 meters
away from the radar antenna.
targets
25
Range [ft]
Dopple
r speed [
m/s
]
Nonlinear Moving Target
-10 0 10 20 30 40-1.5
-1
-0.5
0
0.5
1
-40
-35
-30
-25
-20
-15
-10
-5
0
Harmonic Step-Frequency
Radar: Summary
Tx
Rx
We have (a) shown that RF electronics react harmonically to incident RF waves,
which enables detection of these targets
(b) demonstrated that transmitting low-duty-cycle / high-peak-power is best
for receiving stronger responses from these targets
(c) applied the stepped-frequency concept to harmonic radar,
which enables ranging of RF electronic targets, and
(d) developed an experimental prototype of a stepped-frequency harmonic radar,
which is able to detect & locate commercially-available RF electronic devices.
We intend to (e) package the radar onto a mobile platform (vehicle), and
(f) develop signal-processing techniques to identify particular targets.
26
References
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