maximizing harmonic-radar target response:...

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


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












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


VTx


Experiment

pictures from [7]

A GTEM cell is essentially

a large, flared waveguide.

15

target placement GTEM cell, inside

antenna, absorber

VTx

VTx


Experiment

A GTEM cell is essentially

a large, flared waveguide. Gigahertz Transverse


16


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












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

[1] C. Vicente and H. L. Hartnagel, “Passive-intermodulation analysis between rough rectangular waveguide flanges,” IEEE Transactions on Microwave Theory and

Techniques, Vol. 53, No. 8, Aug. 2005, pp. 2515–2525.

[2] H. Huan and F. Wen-Bin, “On passive intermodulation at microwave frequencies,” in Proceedings of the Asia-Pacific Electromagnetic Conference, Nov. 2003, pp.

422–425.

[3] J. Henrie, A. Christianson, and W. J. Chappell, “Prediction of passive intermodulation from coaxial connectors in microwave networks,” IEEE Transactions on

Microwave Theory and Techniques, Vol. 56, No. 1, Jan. 2008.

[4] G. C. Bailey and A. C. Ehrlich, “A study of RF nonlinearities in nickel,” Journal of Applied Physics, Vol. 50, No. 1, Jan. 1979, pp. 453-461.

[5] J. R. Wilkerson, K. G. Gard, A. G. Schuchinsky, and M. B. Steer, “Electro-thermal theory of intermodulation distortion in lossy microwave components,” IEEE

Transactions on Microwave Theory and Techniques, Vol. 56, No. 12, Dec. 2008.

[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, K. A. Gallagher, A. F. Martone, K. D. Sherbondy, and R. M. Narayanan, “Short-range harmonic radar: Chirp waveform, electronic targets,”

Proceedings of the SPIE, Vol. 9461, pp. 946108(1-12), Apr. 2015.

[13] 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.

[14] 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.

[15] 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.

[16] K. A. Gallagher, G. J. Mazzaro, A. F. Martone, K. D. Sherbondy, and R. M. Narayanan, “Filter selection for a harmonic radar,” Proceedings of the SPIE, Vol.

9461, pp. 94610A(1-11), Apr. 2015.

[17] 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,”

Proceedings of the IEEE Radar Conference, pp. 1428-1433, May 2015.

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