1. science
2. physics
3. optics

03-Apr-2015
Nonlinear Radar for Remotely Locating
and Identifying Electronic Devices
Gregory J. Mazzaro
The Citadel, The Military College of South Carolina
Charleston, SC 29409
Anthony F. Martone
U.S. Army Research Laboratory
Adelphi, MD 20783
Kyle A. Gallagher
Pennsylvania State University
University Park, PA 16802
THE CITADEL, THE MILITARY COLLEGE OF SOUTH CAROLINA
171 Moultrie Street, Charleston, SC 29409
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
2
Nonlinear Radar Concept
electronic
target
Tx
Target presence/location
is indicated by receiving
frequencies that were
not transmitted.
Rx
Applications:
• locate personal electronics during emergencies
• detect electronically-triggered devices
Advantages:
•
It is easier to separate targets from clutter because most clutter is linear.
Disadvantages:
•
Targets require high incident power to drive them into non-linear behavior.
•
Received responses are usually very weak compared to the transmitted “probe” signals.
3
Linearity vs. Nonlinearity
input
For a linear system,
output
x1  y 1

x2  y2
a 1 x1  a 2 x 2  a 1 y 1  a 2 y 2
A0 c o s   0 t   A0  H   0   c o s  0 t     0 
For a non-linear system,
?
a 1 x1  a 2 x 2  a 1 y 1  a 2 y 2
A0 c o s   0 t   A0  H

 A0 ,  0   c o s   A0 ,  0  t    A0 ,  0 
 Transfer function depends on amplitude,
and output frequency does not necessarily equal input frequency.
4
Sources of Nonlinearity
Active elements & components – by design; above system noise floor
diodes
transistors
amplifiers
mixers
+
+
_
f1
f1 + f2
f2
_
Passive elements & components – unintended; below system noise floor
contacts [1,2]
metal 1
connectors [3]
thermal
effects [5]
ferro-electrics [4]
oxide
V
metal 2
R
metal
Nearly all electronics are nonlinear, to some degree.
5
Temperature-Dependent
Resistance
voltage applied,
current flows
Iout
Vin
R
resistance
increases
resistor
heats up
current
increases
Vin
R
current
decreases
resistor cools
down
resistance
decreases
Iout
input: constant
output: sinusoidal
 nonlinear
time
time
6
time
Nonlinear Radar Research
Tx
Rx
Ein
one possible
signal path:
Erefl
...
LNA
BPF
7
We view each target as
a collection of RF
nonlinearities.
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?
8
This type of
radar research
is in its infancy.
Harmonic Radar Theory
from [7]
Let the input waveform be a sinusoid:
Let the nonlinearity
be approximated by
a power series [6]
E in  E 0 c o s   0 t 
input
E o u t  a 1 E in  a 2 E in  a 3 E in  ...
2
3
output
Then the device response (output) is
2
E out
3
 a 1  E 0 c o s   0 t    a 2  E 0 c o s   0 t    a 3  E 0 c o s   0 t    ...




2
E out  a1 E 0 c o s   0 t 

a2 E0
2
3
 1  c o s  2  0 t  

a3 E 0
4
 3 c o s   0 t   c o s  3  0 t  
origin of harmonics
9
 ...
Harmonic Radar Theory:
Time Domain
Let the input be a single tone,
at 1 MHz with amplitude = 1 V:
V in  V 0 c o s   0 t 
V0  1 V
f0 
0
2
 1 MHz
input
output
The output is a sum of sinusoids
at 1 MHz, 2 MHz, 3 MHz, etc:
V o u t   1V 0 c o s   0 t    2 V 0 c o s  2  0 t 
2
In the time domain, nonlinearity
manifests itself as waveform distortion
(e.g. rectification, saturation).
  3V 0 c o s  3  0 t    4 V 0 c o s  4  0 t 
3
4
  5V 0 c o s  5  0 t    6 V 0 c o s  6  0 t   ...
5
6
10
Harmonic Radar Theory:
Frequency Domain
Let the input be a single tone,
at 1 MHz with amplitude = 1 V:
V in  V 0 c o s   0 t 
input = { f }
V0  1 V
f0 
0
2
 1 MHz
output = { f, 2f, 3f, 4f, 5f, 6f, … }
input
output
The output is a sum of sinusoids
at 1 MHz, 2 MHz, 3 MHz, etc:
V o u t   1V 0 c o s   0 t    2 V 0 c o s  2  0 t 
2
  3V 0 c o s  3  0 t    4 V 0 c o s  4  0 t 
3
4
  5V 0 c o s  5  0 t    6 V 0 c o s  6  0 t   ...
5
6
In the frequency domain, nonlinearity
manifests itself as spurious spectral content
(e.g. harmonics, intermodulation).
11
Harmonic Radar Theory:
Frequency Domain
f1  9 9 M H z
input
f1  9 9 M H z
f2  101 M H z
f2  101 M H z
output
intermodulation
harmonics
difference / “beat”
frequencies
In the frequency domain, nonlinearity
manifests itself as spurious spectral content
(e.g. harmonics, intermodulation).
12
Prior (Published) Work
RADAR TAGS for INSECT TRACKING
[9]
[8]
AUTOMOTIVE RADAR for detecting
“VULNERABLE ROAD USERS”
MILITARY RADAR for detecting
MANMADE METALLIC OBJECTS
[10]
[11]
• simulations show detection possible > 22 m at 80 GHz
NLR for detecting
RF devices is novel.
13
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
14
1-Tone Continuous-Wave
Experiment
Tektronix AWG7052
arbitrary waveform generator
Amplifier Research
50-W 1-GHz RF amplifier
step
attenuator
Gigahertz Transverse
Electromagnetic cell
target
Ptrans
antenna
Prec
Rohde & Schwarz FSP
40-GHz spectrum analyzer
We performed our initial nonlinear (harmonic) experiments
wirelessly, at high power, in a controlled environment.
15
1-Tone Continuous-Wave
Experiment
pictures from [7]
Gigahertz Transverse
Electromagnetic cell
A GTEM cell is essentially
a large, flared waveguide.
VTx
GTEM cell, outside, front
GTEM cell, outside, back
16
1-Tone Continuous-Wave
Experiment
A GTEM cell is essentially
a large, flared waveguide.
Gigahertz Transverse
Electromagnetic cell
antenna, absorber
VTx
target placement
GTEM cell, inside
VTx
17
1-Tone Continuous-Wave
Measurements
GTEM cell
We found that many commercially-available RF devices
respond harmonically to incident continuous waves.
18
1-Tone Results:
Publication
[12]
The harmonic responses of cell phones & radios
were experimentally demonstrated, but
ranging of targets is not possible with a single antenna
and a single continuous frequency.
19
Processed
Received
Transmitted
(Linear)
Stepped-Frequency Radar
…
amplitude
A1
A2
A3
A4
A5
phase
f1
f2
f3
f4
f5
…
…
frequency
f0
f0 + Df
f0 + 2Df
f0 + 3Df
f0 + 4Df
…
IDFT
R 
c
After constructing H() of the
environment, an inverse DFT
gives its impulse response.
t
2
20
Processed
Received
Transmitted
Nonlinear
Stepped-Frequency Radar
…
amplitude
A1
A2
A3
A4
A5
phase
f1
f2
f3
f4
f5
…
…
2f0
2f0 + 2Df
2f0 + 4Df
2f0 + 6Df
2f0 + 8Df
…
frequency
IDFT
R 
c
After constructing H() of the
environment, an inverse DFT
gives its impulse response.
t
2
21
Nonlinear SFR:
Hardware Simulation
figure adapted from [13]
oscilloscope
channel A
Vtrans
Simulated Radar
Environment
Transmitter
target
d = 100 ft
Vrec
oscilloscope
channel B
Receiver
Our first stepped-frequency experiment
was a bench-top (coaxial-only) test.
22
Nonlinear SFR:
Hardware Simulation
red = received from target,
1760 to 1840 MHz
blue = transmitted to target,
880 MHz to 920 MHz
target
We transmitted a sequence of
frequencies and we received a
sequence at twice these frequencies.
23
Nonlinear SFR:
Hardware Simulation
Because (a) the phase response of the
target is linear and (b) the amplitude
response is ~flat over the band of
interest…
hNL  t  
s in  B tg t  t  2 
  t  2


M 1
EM E0

e
j2

f tg t
 t  2 
 nonlinear impulse response,
constructed from an IDFT
of the data in red
d  100 ft
d 
As with linear step-freq radar,
range-to-target was found using
an inverse Fourier Transform.
1
2
24
t 
c
r
ft 

  0 .3 4
t
n
s


Nonlinear SFR:
Hardware Simulation
target
The distance-to-target
calculation was verified using
4 different lengths of coaxial cable.
25
Nonlinear SFR:
Planned Experiment
targets
adapted from [14]
12 ft
target
Ptrans
Prec
Goal #1: Perform wireless experiments
and verify NL SFR concept with
multiple electronic targets.
26
Nonlinear SFR:
Over-the-Air Experiment
Tx/Rx
antenna
metal-free
experimental
enrivonment
at ARL
signal generation
& capture
Goal #2: Use available RF instruments
to perform the experiment.
27
Nonlinear Step-Freq Radar:
Experiment
We set up our antenna and targets in a low-metal-content
environment at ARL’s Adelphi Laboratory Center.
target location
12 ft
( all targets were place
with antennas oriented
vertically )
quad-ridge
horn antenna
28
Nonlinear Step-Freq Radar:
Experiment
Most of the prototype radar hardware
pieces were commercial off-theshelf components or standard radiofrequency laboratory instruments.
20GS/s
oscilloscope
power
amplifier
Data capture and processing were
performed on a laptop, in Matlab.
arbitrary
waveform
generator
to scope
directional
coupler
to/from
antenna
from power
amplifier
triple-voltage
power
supplies
low-noise
amps x3
to scope
29
diplexers
x2
Nonlinear SFR:
Over-the-Air Experiment
figure adapted from [14]
transmit
waveform:
fstart = 700 MHz
fend = 900 MHz
8 ms
2 ms
diplexers (x2)
50 W
f0
f0
target
oscilloscope
channel A
oscilloscope
channel B
2f0
2f0
~2 W transmitted
Diplexers were implemented to (a) transmit & receive on a single antenna,
(b) lowpass-filter the transmit signal, and (c) highpass-filter the receive signal.
30
Over-the-Air NL SFR:
Highly Linear Transceiver
diplexers designed by K. Gallagher
and fabricated by A. Owens [15]
Tx band
Rx band
~36 dB
gain
~50 dB
gain
The receiver amplifies each
harmonic received from the
antenna by ~50 dB.
The transmitter amplifies each tone
by ~36 dB to send 2 Watts to the
antenna at each frequency.
31
Processed
Received
Transmitted
2nd-Harmonic
Stepped-Frequency Radar
…
amplitude
A1
A2
A3
A4
A5
phase
f1
f2
f3
f4
f5
…
…
2f0
2f0 + 2Df
2f0 + 4Df
2f0 + 6Df
2f0 + 8Df
…
frequency
IDFT
R 
c
After constructing H() of the
environment, an inverse DFT
gives its impulse response.
t
2
32
Nonlinear Step-Freq Radar:
Results
targets
Both targets were detected,
individually and simultaneously,
up to a distance of 7 meters
away from the radar antenna.
These results will be presented at
SPIE Defense, Security, & Sensing 2015
in Baltimore, MD (20 Apr 2015).
33
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
34
NL SFR Moving Target
Experiment
[16]
One of the targets was placed on a moving platform.
During data capture, the target moved towards the radar.
NI-5651
50 Ω
Coupler
-23 dB
C
H
L
H
L
PA
C
H
L
C
H
50 Ω
C
Tx
L
NI Chassis
With LabView
Ref
LeCroy O-Scope
10 Gsamp/sec
8 Bits
NL
Rec
AMP
3 dB
Att.
LNA
C
Linear
Rec
H
L
C
50 Ω
H
L
H
L
50 Ω
50 Ω
C
Mini-Circuits Diplexers
35
H
L
C
LNA
H
L
C
Rx
50 Ω
High Power Reactel Diplexer
NL SFR Moving Target
Results
[16]
One of the targets was placed on a moving platform.
During data capture, the target moved towards the radar.
Nonlinear Moving Target
1
0
Doppler speed [m/s]
-10
-15
0
-20
-0.5
-25
-30
-1
-35
-1.5
-10
0
10
20
30
40
-40
Range [ft]
36
Received Power
(dBsm, normalized)
-5
0.5
These results will be presented at the
IEEE International Radar Conference
in Arlington, VA (May 2015).
Harmonic Step-Frequency
Radar: Summary
Nonlinear Moving Target
Tx
1
0
-5
0.5
Doppler speed [m/s]
-10
Rx
-15
0
-20
-0.5
-25
-30
-1
-35
-1.5
-10
0
10
20
30
40
Range [ft]
We have (a) demonstrated that RF electronics react harmonically to incident RF waves,
which enables detection of these targets
(b) applied the stepped-frequency concept to harmonic radar,
which enables ranging of RF electronic targets, and
(c) developed an experimental prototype of a stepped-frequency harmonic radar,
which is able to determine location, direction, & speed of an RF target.
We intend to (d) package the radar onto a mobile platform (vehicle), and
(e) develop signal-processing techniques to identify particular targets.
37
-40
References
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2003, pp. 422–425.
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Transactions on Microwave Theory and Techniques, Vol. 56, No. 1, Jan. 2008.
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[6] J. C. Pedro and N. B. Carvalho, Intermodulation Distortion in Microwave and Wireless Circuits. Boston, MA: Artech House, 2003.
[7] G. J. Mazzaro and A. F. Martone, “Harmonic and multitone radar: Theory and experimental apparatus,” U.S. Army Research Laboratory Technical
Report, No. 6235, Oct. 2012.
[8] N. Tahir and G. Brooker, “Recent developments and recommendations for improving harmonic radar tracking systems,” in Proceedings of the 5th
European Conference on Antennas and Propagation, Apr. 2011, pp. 1531–1535.
[9] D. Psychoudakis, W. Moulder, C. C. Chen, H. Zhu, and J. L. Volakis, “A portable low-power harmonic radar system and conformal tag for insect
tracking”, IEEE Antennas and Wireless Propagation Letters, Vol. 7, 2008, pp. 444–447.
[10] J. Saebboe, V. Viikari, T. Varpula, and H. Seppa, “Harmonic automotive radar for VRU classification”, in Proceedings of the International Radar
Conference: Surveillance for a Safer World, Oct. 2009, pp. 1–5.
[11] C. L. Opitz, “Radar object detector using non-linearities,” U. S. Patent 4,053,891, Oct. 11, 1977.
[12] G. J. Mazzaro, A. F. Martone, and D. M. McNamara, “Detection of RF electronics by multitone harmonic radar,” IEEE Transactions on Aerospace and
Electronic Systems, Vol. 50, No. 1, Jan. 2014.
[13] G. J. Mazzaro, K. A. Gallagher, A. F. Martone, and R. M. Narayanan, “Stepped-frequency nonlinear radar simulation,” Proceedings of the SPIE, Vol.
9077, pp. 90770U(1-10), May 2014.
[14] G. J. Mazzaro, K. A. Gallagher, A. R. Owens, K. D. Sherbondy, and R. M. Narayanan, “Ultra-wideband harmonic radar for locating radio-frequency
electronics,” U.S. Army Research Laboratory Technical Report, No. 7256, Mar. 2015.
[15] K. A. Gallagher, G. J. Mazzaro, A. F. Martone, K. D. Sherbondy, and R. M. Narayanan, “Filter selection for a harmonic radar receiver,” accepted to
SPIE Defense, Security, & Sensing 2015, Baltimore, MD, April 2015.
[16] K. A. Gallagher, R. M. Narayanan, G. J. Mazzaro, K. I. Ranney, A. F. Martone, and K. D. Sherbondy, “Moving target indication with non-linear radar,”
accepted to 2015 IEEE International Radar Conference, Arlington, VA, May 2015.
38