Reflection Phase Surfaces for Cognitive Radar and ... · Reflection Phase Surfaces for Cognitive Radar and Broadband Antenna Enhancement Amir I. Zaghloul U.S. Army Research Laboratory,

Forum for Electromagnetic Research Methods and Application Technologies (FERMAT)

Reflection Phase Surfaces for Cognitive Radar and Broadband Antenna Enhancement

Amir I. Zaghloul

U.S. Army Research Laboratory, Adelphi, MD 20783

Keywords: Cognitive Radar, Wideband EBG Designs, Active Reflection Phase Surfaces, Enhanced UWB Antenna.

Outline

• Introduction

• Cognitive Radar

• Reflection Phase off EBG Surfaces

• Wideband EBG Designs

• Active Reflection Phase Surfaces

• EBG-Backed Spiral Antenna

• Enhanced UWB Antenna

• Conclusion

Outline

• Introduction

• Cognitive Radar






• Conclusion

• Cognitive Radar is based on learning through interactions of

the radar with the environment

• Information is facilitated by feedback from the receiver to

the transmitter

• Information on target is deduced through processing of

radar returns

• Environment or channel data include reflection phase and

resonance frequencies of surfaces, which constitute part of

the feedback from the receiver to the transmitter

• Adaptive reflection phase control can be a key function

Introduction

Block diagram of cognitive radar viewed as a dynamic closed-

loop feedback system*

* S. Haykin, “Cognitive Radar, A way of the future,” IEEE Signal Processing Magazine, January 2006

Cognitive Radar Concept

Quotes from S. Haykin

• For the radar to be cognitive, adaptivity has to be extended to the

transmitter too

• The function of the radar-scan analyzer is to provide the receiver

with information on the environment

• The selection of waveforms to be used for adaptive radar

transmission is application dependent

• There is much that we can learn from the echo-location system of

a bat

• An echo-locating bat can pursue and capture its target with a

facility and success rate that would be the envy of a radar engineer

Adaptive Reflection Phase

• Adaptively control the environment, primarily reflection

function

• Function of phase variation can be controlled by transmitter

and shared by receiver

• Narrow-band fast phase change or wide-band slow phase

change versus frequency

• Introduces false target information in radar jamming

systems

• Can be effective in Digital Radio Frequency Memory

(DRFM) techniques

Outline

• Introduction

• Cognitive Radar






• Conclusion

9

• EBG structures are usually periodic

• High surface impedance

• Do not support surface waves

• Useful when mounting an antenna close to a ground plane

• EBG structures are compact in size, have low loss, and

can be integrated into an antenna

Electromagnetic Band Gap (EBG)

Surfaces

102010 National Radio Science Meeting, Boulder| Session BS2-3.

• In phase reflection of the wave

• Band Gap is the frequencies where the

reflected phase is between +900 and -900

• Usually narrowband

Regular EBG Structures

Reflection Phase off EBG Surfaces

Mushroom EBG Configuration and Reflection Phase*

Variation of Frequency Response of Reflection

Phase with Patch Dimensions***Sievenpiper et al., IEEE Trans MT&T, Nov 1999

** Nakano et al., IEEE Trans A&P, May 2009

Outline

• Introduction

• Cognitive Radar






• Conclusion

Wide-Band Slow-Phase-Variation

EBG Surfaces

Reflection Phase Vs. Frequency

-250

-200

-150

-100

-50

0

50

100

150

200

250

9 10 11 12 13 14 15 16 17 18 19 20

Freq. (GHz)

Re

fle

cti

on

Ph

as

e (

De

g)

Uniform EBG Progressive EBG

Frequency response of reflection phase for

uniform (fast) and progressive (slow) EBG*

Frequency response of reflection phase for

uniform (fast) and stacked (slow) EBG**

*Zaghloul, Palreddy. Weiss, EuCAP 2011

** Palreddy, Zaghloul, Lee, EuCAP 2012

Outline

• Introduction

• Cognitive Radar






• Conclusion

Tunable EBG Surface

Tunable EBG surface using varactor diodes

Dual Band Tunable EBG

EBG surface independently tuned over two separate

frequency bands using dual layer with varactor diodes*Lee, Ford, Langley, Electronics Letters, 2008

Tunable Surface Using Distributed

MEMS

S21-Parameter for unit EBG cellSchematic of unit EBG cell

Top view of tunable structure

*Zhang et al., IEEE Nano/Micro Engineered, 2009

Outline

• Introduction

• Cognitive Radar






• Conclusion


• Formed by cascading Uniform EBGs of same height

• Resonate close to one another

• Has a wider band gap than regular EBG

EBG-Backed Spiral Antenna

20

• Computed using FEKO

• Reflection phase computed just above the EBG surface

• Notice that the Progressive EBG structure has wider band gap.

Reflection Phase Comparison


Gain patterns of the spiral antenna in free space

Spiral Antenna in Free Space

Gain patterns of the spiral antenna near uniform EBG

22

Spiral Antenna near Uniform

EBG

Gain patterns of the spiral antenna near progressive EBG

23

Spiral Antenna near

Progressive EBG

Return Loss comparison of the spiral antenna under

different loading conditions

24

Return Loss Comparison

25

Boresight gain comparison of the spiral antenna under

different loading conditions

Boresight Gain Comparison

26

Boresight axial ratio comparison of the spiral antenna

under different loading conditions

Axial Ratio Comparison

27

• Higher gain and higher front-to-back ratio with progressive EBG

• Better boresight axial ratio performance with progressive EBG

than Uniform EBG

• Uniform height progressive EBG structure has a wider band gap,

compared to the regular EBG structure

• Accomplished with low profile that is afforded by the reflection

phase characteristics of the broadband EBG

• This low profile is in contrast with the higher profile design that

uses PEC-backed or absorber-backed cavities

• Gain patterns of the antenna near progressive EBG are cleaner &

smoother, like the case in free space, compared to the case near

uniform EBG

Features of Spiral Antenna near

Progressive EBG

Outline

• Introduction

• Cognitive Radar






• Conclusion

Yagi Antenna Concept

Enhanced UWB Antenna

Stacked Patches for Broader

Bandwidth or Multiple Bands

UWB Monopole Antenna

Basic coplanar-waveguide-fed circular monopole

E-plane

H-plane

Monopole + Director + EBG

Reflector

Monopole

ElementDirector

Element

EBG

Reflector

Surface

Radiation

• Director element: same size as monopole, or

different, depending on wideband, multiple-band

requirements

• EBG surface: single resonance, multiple-

resonance progressive, multiple-resonance stacked

Return Loss of Basic UWB

Element

Frequency (GHz)

S11

(dB

)

Radiation Pattern of Basic UWB

Monopole

-38.00

-26.00

-14.00

-2.00

90

60

30

0

-30

-60

-90

-120

-150

-180

150

120

HFSSDesign1Radiation Pattern 700 MHz ANSOFT

m1

Curve Info

dB(RealizedGainTotal)Setup1 : LastAdaptiveFreq='0.7GHz' Phi='0deg'


Name Theta Ang Mag

m1 360.0000 -0.0000 1.7859

-30.00

-20.00

-10.00

0.00

90

60

30

0

-30

-60

-90

-120

-150

-180

150

120

HFSSDesign1Radiation Pattern 3 GHz ANSOFT

Curve Info

dB(RealizedGainTotal)Setup1_1_1_1_1_1_1_1_1_1_1_1 : LastAdaptiveFreq='3GHz' Phi='0deg'

dB(RealizedGainTotal)Setup1_1_1_1_1_1_1_1_1_1_1_1 : LastAdaptiveFreq='3GHz' Phi='90deg'

-27.00

-19.00

-11.00

-3.00

90

60

30

0

-30

-60

-90

-120

-150

-180

150

120


Curve Info

dB(RealizedGainTotal)Setup1_1_1_1_1_1_1_1 : LastAdaptiveFreq='2GHz' Phi='0deg'


E- (purple) and H- (red) plane patterns of

basic UWB monopole at band edges and

center

Return Loss of UWB Monopole

with a Director

S11

(dB

)

Frequency (GHz)

Realized Gain of Monopole

with and w/o Director

Blue: w/o director, Red with director

Frequency (GHz)

Re

aliz

ed

Ga

in (

dB

i)

Radiation Pattern of UWB

Monopole and Director

-38.00

-26.00

-14.00

-2.00

90

60

30

0

-30

-60

-90

-120

-150

-180

150

120

Ansoft LLC HFSSDesign1Radiation Pattern 0.7 GHz ANSOFT

m1

m2

Curve Info



Name Theta Ang Mag

m1 360.0000 -0.0000 2.4819

m2 180.0000 180.0000 -2.3237

-30.00

-20.00

-10.00

0.00

90

60

30

0

-30

-60

-90

-120

-150

-180

150

120

Ansoft LLC HFSSDesign1Radiation Pattern 2 GHz ANSOFT

m1 m2

Curve Info

dB(RealizedGainTotal)Setup13 : LastAdaptiveFreq='2GHz' Phi='0deg'


Name Theta Ang Mag

m1 360.0000 -0.0000 -2.1669

m2 30.0000 30.0000 2.8062

-38.00

-26.00

-14.00

-2.00

90

60

30

0

-30

-60

-90

-120

-150

-180

150

120

Ansoft LLC HFSSDesign1Radiation Pattern 3 GHz ANSOFT

Curve Info




UWB monopole plus director at band

edges and center

Red: no EBG, blue: one layer EBG, no director present

Realized Gain of Monopole

with and w/o EBG Reflector

0.70 1.20 1.70 2.20 2.70 3.00Freq [GHz]

-60.00

-50.00

-40.00

-30.00

-20.00

-10.00

0.00

dB

(S(L

um

pP

ort

1,L

um

pP

ort

1))

S11 EBG + Director ANSOFT

Curve Info

dB(S(LumpPort1,LumpPort1))Setup1 : Sw eep1L='1.6in' r1='2in'

S11

(dB

)

Frequency (GHz)

Return Loss of UWB Monopole

with a Director and EBG

Radiation Pattern of UWB

Monopole with Director and EBG

-18.00

-11.00

-4.00

3.00

90

60

30

0

-30

-60

-90

-120

-150

-180

150

120

Ansoft LLC HFSSDesign1Radiation Pattern 700 MHz ANSOFT

Curve Info



-18.00

-11.00

-4.00

3.00

90

60

30

0

-30

-60

-90

-120

-150

-180

150

120

HFSSDesign1Radiation Pattern 2.8 GHz ANSOFT

Curve Info

dB(RealizedGainTotal)Setup1_1_1_1_1_1_1_1_1_1_1_1 : LastAdaptiveFreq='2.8GHz' Phi='0deg'

dB(RealizedGainTotal)Setup1_1_1_1_1_1_1_1_1_1_1_1 : LastAdaptiveFreq='2.8GHz' Phi='90deg'

-14.00

-8.00

-2.00

4.00

90

60

30

0

-30

-60

-90

-120

-150

-180

150

120


Curve Info




UWB monopole with director and EBG

reflector at band edges and center

Realized Gain of UWB

Monopole Configurations

Outline

• Introduction

• Cognitive Radar






• Conclusion

Conclusions

• Adaptive reflection phase surfaces can be effective elements in the

tool box for cognitive radar

• Frequency-dependent phase responses add to the environment

control that is key to the operation of cognitive radar

• Changing phase information of surfaces can help in the process of

anti-jamming

• Current designs of reflection phase control include varactor diodes

and MEMS

• Rate of phase change with frequency can be a key parameter in the

design that also depends on the narrowband and wideband operations

• Tunable impedance surfaces are capable of steering radio frequency

beams in controllable directions, a desired feature in cognitive radar

14

• Uniform EBG structures are helpful, but they have narrow

band gap

• Progressive EBG structures formed by cascading Uniform

EBG structures

• Progressive EBG has wider band gap compared to

Uniform EBG

• Progressive EBG is preferable with broadband antennas

Conclusions (cont.)

• Basic UWB circular monopole element has gain variation of 15

dB over the band of 700-3000 MHz

• Director increases gain at the upper half of the band

• EBG increases the gain across the band, but more around its

resonance frequency

• Broadband EBG would increase the gain more over the whole

wide band

• Combination of director and EBG reflector equalizes the gain

over the full wide band with gain variation less than 4 dB

Conclusions (cont.)

Documents

Reflection Phase Surfaces for Cognitive Radar and ... · Reflection Phase Surfaces for Cognitive Radar and Broadband Antenna Enhancement Amir I. Zaghloul U.S. Army Research Laboratory,