Reflection Phase Surfaces for Cognitive Radar and ... · Reflection Phase Surfaces for Cognitive...
Transcript of Reflection Phase Surfaces for Cognitive Radar and ... · Reflection Phase Surfaces for Cognitive...
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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.
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Outline
• Introduction
• Cognitive Radar
• Reflection Phase off EBG Surfaces
• Wideband EBG Designs
• Active Reflection Phase Surfaces
• EBG-Backed Spiral Antenna
• Enhanced UWB Antenna
• Conclusion
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Outline
• Introduction
• Cognitive Radar
• Reflection Phase off EBG Surfaces
• Wideband EBG Designs
• Active Reflection Phase Surfaces
• EBG-Backed Spiral Antenna
• Enhanced UWB Antenna
• Conclusion
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• 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
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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
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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
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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
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Outline
• Introduction
• Cognitive Radar
• Reflection Phase off EBG Surfaces
• Wideband EBG Designs
• Active Reflection Phase Surfaces
• EBG-Backed Spiral Antenna
• Enhanced UWB Antenna
• Conclusion
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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
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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
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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
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Outline
• Introduction
• Cognitive Radar
• Reflection Phase off EBG Surfaces
• Wideband EBG Designs
• Active Reflection Phase Surfaces
• EBG-Backed Spiral Antenna
• Enhanced UWB Antenna
• Conclusion
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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
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Outline
• Introduction
• Cognitive Radar
• Reflection Phase off EBG Surfaces
• Wideband EBG Designs
• Active Reflection Phase Surfaces
• EBG-Backed Spiral Antenna
• Enhanced UWB Antenna
• Conclusion
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Tunable EBG Surface
Tunable EBG surface using varactor diodes
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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
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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
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Outline
• Introduction
• Cognitive Radar
• Reflection Phase off EBG Surfaces
• Wideband EBG Designs
• Active Reflection Phase Surfaces
• EBG-Backed Spiral Antenna
• Enhanced UWB Antenna
• Conclusion
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192010 National Radio Science Meeting, Boulder| Session BS2-3.
• 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
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• Computed using FEKO
• Reflection phase computed just above the EBG surface
• Notice that the Progressive EBG structure has wider band gap.
Reflection Phase Comparison
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212010 National Radio Science Meeting, Boulder| Session BS2-3.
Gain patterns of the spiral antenna in free space
Spiral Antenna in Free Space
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Gain patterns of the spiral antenna near uniform EBG
22
Spiral Antenna near Uniform
EBG
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Gain patterns of the spiral antenna near progressive EBG
23
Spiral Antenna near
Progressive EBG
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Return Loss comparison of the spiral antenna under
different loading conditions
24
Return Loss Comparison
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Boresight gain comparison of the spiral antenna under
different loading conditions
Boresight Gain Comparison
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Boresight axial ratio comparison of the spiral antenna
under different loading conditions
Axial Ratio Comparison
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• 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
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Outline
• Introduction
• Cognitive Radar
• Reflection Phase off EBG Surfaces
• Wideband EBG Designs
• Active Reflection Phase Surfaces
• EBG-Backed Spiral Antenna
• Enhanced UWB Antenna
• Conclusion
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Yagi Antenna Concept
Enhanced UWB Antenna
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Stacked Patches for Broader
Bandwidth or Multiple Bands
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UWB Monopole Antenna
Basic coplanar-waveguide-fed circular monopole
E-plane
H-plane
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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
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Return Loss of Basic UWB
Element
Frequency (GHz)
S11
(dB
)
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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'
dB(RealizedGainTotal)Setup1 : LastAdaptiveFreq='0.7GHz' Phi='90deg'
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
HFSSDesign1Radiation Pattern 2 GHz ANSOFT
Curve Info
dB(RealizedGainTotal)Setup1_1_1_1_1_1_1_1 : LastAdaptiveFreq='2GHz' Phi='0deg'
dB(RealizedGainTotal)Setup1_1_1_1_1_1_1_1 : LastAdaptiveFreq='2GHz' Phi='90deg'
E- (purple) and H- (red) plane patterns of
basic UWB monopole at band edges and
center
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Return Loss of UWB Monopole
with a Director
S11
(dB
)
Frequency (GHz)
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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)
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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
dB(RealizedGainTotal)Setup1 : LastAdaptiveFreq='0.7GHz' Phi='0deg'
dB(RealizedGainTotal)Setup1 : LastAdaptiveFreq='0.7GHz' Phi='90deg'
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'
dB(RealizedGainTotal)Setup13 : LastAdaptiveFreq='2GHz' Phi='90deg'
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
dB(RealizedGainTotal)Setup18 : LastAdaptiveFreq='3GHz' Phi='0deg'
dB(RealizedGainTotal)Setup18 : LastAdaptiveFreq='3GHz' Phi='90deg'
E- (purple) and H- (red) plane patterns of
UWB monopole plus director at band
edges and center
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Red: no EBG, blue: one layer EBG, no director present
Realized Gain of Monopole
with and w/o EBG Reflector
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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
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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
dB(RealizedGainTotal)Setup1 : LastAdaptiveFreq='0.7GHz' Phi='0deg'
dB(RealizedGainTotal)Setup1 : LastAdaptiveFreq='0.7GHz' Phi='90deg'
-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
HFSSDesign1Radiation Pattern 2 GHz ANSOFT
Curve Info
dB(RealizedGainTotal)Setup1_1_1_1_1_1_1_1 : LastAdaptiveFreq='2GHz' Phi='0deg'
dB(RealizedGainTotal)Setup1_1_1_1_1_1_1_1 : LastAdaptiveFreq='2GHz' Phi='90deg'
E- (purple) and H- (red) plane patterns of
UWB monopole with director and EBG
reflector at band edges and center
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Realized Gain of UWB
Monopole Configurations
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Outline
• Introduction
• Cognitive Radar
• Reflection Phase off EBG Surfaces
• Wideband EBG Designs
• Active Reflection Phase Surfaces
• EBG-Backed Spiral Antenna
• Enhanced UWB Antenna
• Conclusion
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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
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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.)
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• 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.)