qun mng

Modelado de Metamateriales para
Aplicaciones en Antenas
Raj Mittra
Electromagnetic Communication Laboratory
Penn State University
E-mail: [email protected]
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TITLES, TITLES—POSSIBLE
CHOICES
META 101
ALL YOU WANTED TO KNOW ABOUT
METAMATERIALS BUT WERE AFRAID TO ASK
WHAT’S NEW ABOUT METAMATERIALS
METAMATERIALS—THE HOLY GRAIL!
METAMATERIAL MODELING FOR ANTENNAS
FINALLY, WE SETTLE ON:
A CASE FOR METAMATERIAL MODELING
CLASSIFICATON OF METAMATERILS
Re[ μ ]
DPS
ENG
MNZ
k ∈ℜ
k ∈ℑ
DNG
k ∈ℜ
ENZ
ENZ
MNZ
Regular
Dielectrics
MNG
k ∈ℑ
Loughborough Antennas and Propagation Conference – 2006
F. Bilotti – Potential Applications of Matamaterials in Antennas
Re[ε ]
Taxonomy of Metamaterials
‰
Double Negative (DNG) materials (Periodicity d << λ)
¾ Elements and distances between them are much smaller than a
wavelength (Effective medium concepts, simultaneous effective
negative permittivity and permeability)
¾ Have several names including left-handed materials, backward-
wave materials, Negative Index of Refraction (NIR) materials,
etc.
‰
Electromagnetic Band Gap (EBG) materials (Periodicity d ~ λ)
¾ Element Distances are on the order of half a wavelength or
more (Periodic medium concepts)
¾ Photonic crystals, Photonic Band Gap materials (PBG), Artificial
Magnetic Conductors (AMC), High Impedance Surfaces (HIS)
Acknowledgement:
The viewgraphs 5-22 are from Prof. Yang Hao
of Queen Mary College, University of London
Electromagnetic Communication Lab
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In a paper published in 2001, Rodger Walser from the
University of Texas, Austin, coined the term
'metamaterial' to refer to artificial composites that
'...achieve material performance beyond the
limitations of conventional composites.'
The definition was subsequently expanded by Valerie
Browning and Stu Wolf of DARPA (Defense
Advanced Research Projects Agency) in the context
of the DARPA Metamaterials program that started
also in 2001. Their basic definition:
– Metamaterials are a new class of ordered composites that
exhibit exceptional properties not readily observed in
nature. These properties arise from qualitatively new
response functions that are: (1) not observed in the
constituent materials and (2) result from the inclusion of
artificially fabricated, extrinsic, low dimensional
inhomogeneities.
Periodic Structures in Nature
and Daily Life
zA
bending light under the conservatory roof
Natural Periodic Structures
Crystal
structure
Butterfly
wings
Bee hive
Artificial Dielectrics
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The first ever known metamaterials, which mimic natural
materials: high contrast lossless dielectrics and absorbers
Usually consist of artificially created 'molecules': dielectric or
metallic inclusions of certain shape. These 'molecules' can be
distributed and oriented either regularly or randomly.
The dimensions of the 'molecules' and characteristic distances
between neighboring ones is much smaller than wavelength.
Can be described in terms of material parameters (permittivity)
The first artificial dielectric was invented by W.E. Kock and used
in design of low-weight dielectric lenses at microwaves
[1] W. Kock, “Metallic delay lenses”, Bell Syst. Tech. J., vol. 27, pp. 58-82,
1948.
[2] R. Collin, Field Theory of Guided Waves. IEEE Press, Piscataway, NJ,
1990.
Wire Medium
z
plasma-like frequency
dependent
permittivity
ω
ε (ω ) = 1 −
ω
z
z
2
0
2
negative below
plasma frequency
positive but less than
unity above omega0
J. Pendry, A. Holden, W. Steward, and I. Youngs, “Extremely low frequency plasmons
in metallic mesostructures”, Phys. Rev. Lett., vol. 76, no. 25, pp. 4773-4776, 1996.
Permittivity of Artificial Dielectrics
[1] J. Brown, “Artificial dielectrics,"
Progress in dielectrics, vol. 2,
pp. 195-225, 1960.
[2] W. Rotman, “Plasma simulations by
artificial dielectrics and parallel-plate
media," IRE Trans. Ant. Propag., vol.
10, pp. 82-95, 1962.
Artificial Magnetics
Magnetic inclusions: a) split-ring-resonator, b) swiss roll
J. Pendry, A. Holden, D. Robbins, W. Stewart, “Magnetism from conductors and enhanced
nonlinear phenomena”, IEEE Trans. Microwave Theory Techn., vol. 47, no. 11, pp. 195225, 1999.
Permeability of Resonant
Magnetics
Characteristic sizes giving
negative μ
–PendryJ et al IEEE Trans
MTT472075 1999
–a ~ λo/ 2
Left-handed Medium (LHM):
Material with Simultaneous
Negative ε and μ
V.G. Veselago, “The electrodynamics
of substances with simultaneously
negative values of ε and μ,” Soviet
Physics Uspekhi, vol. 10, pp. 509-514,
1968.
Right-handed VS Left-handed
Right-handed medium:
vectors E, H and k form
right triple of vectors
Left-handed medium:
vectors E, H and k form
left triple of vectors
Backward waves at beginning of
20th century
H. Lamb [1] may have been the first person who shown the
existence of backward waves (the waves which phase moves in
the direction opposite from that of the energy flow) in mechanical
systems. Seemingly, the first person who discussed the backward
waves in electromagnetism was A. Schuster [2]. On pp. 313-318
Schuster gives a speculative discussion of its implications for
optical refraction. H.C. Pocklington in [3] showed that in a
specific backward-wave medium, a suddenly activated source
produces a wave which group velocity is directed away from the
source, while its velocity moves toward the source.
[1] H. Lamb, “On group-velocity”, Proc. London Math. Soc., vol. 1, pp. 473-479, 1904.
[2] A. Schuster, An Introduction to the Theory of Optics, Edward Arnold, London, 1904.
[3] H. Pocklington, “Growth of a wave-group when the group velocity is negative”,
Nature, vol. 71, pp. 607- 608, 1905.
Backward waves in left-handed
transmission lines in 50ths
[1] G.D. Malyuzhinets, “A note on the radiation principle”, Zh. Tekh. Fiz., Vol. 21, pp. 940-942, 1951.
[2] A. Grbic and G. Eleftheriades, “Periodic analysis of a 2-D negative refractive index transmission
line structure,” IEEE Trans. Antennas Propagation, vol. 51, no. 10, pp. 2604-2611, 2003.
Positive and Negative Refraction
Positive refraction:
from ordinary dielectric
to ordinary dielectric
Negative refraction:
from ordinary dielectric
to left-handed medium
Negative Refraction in
Academician
L.I. Mandelshtam
(1879-1944)
s
40
Imaging by Pendry’s Perfect Lens
far field
near field
Photonic (electromagnetic) Crystals
z
z
z
z
Periodical structures with lattice periods
comparable to wavelengths
Band gaps: frequency bands where the material
does not support propagating waves
Spatial and frequency dispersion: material
parameters depend on the wave vector as well as
on the frequency
Strong localization of photons and inhibited
spontaneous emission due to photonic bandgaps
[1] E. Yablonovitch, “Inhibited spontaneous emission in solid-state physics and
electronics,” Phys. Rev. Lett., vol. 58, no. 20, pp. 2059–2062, 1987.
[2] S. John, “Strong localization of photons in certain disordered dielectric superlattices,”
Phys. Rev. Lett., vol. 58, no. 23, pp. 2486–2489, 1987.
Example of Photonic Crystal with
Complete Bandgap
E. Yablonovitch, T. Gmitter, and K. Leung, “Photonic band structure: the face-centered-cubic
case employing nonspherical atoms,” Phys. Rev. Lett., vol. 67, no. 17, pp. 2295–2298, 1991.
QUESTION, QUESTION
Q. SO WHAT EXOTIC THINGS WOULD
YOU DO WITH METAMATERIALS, IF
YOU HAD THEM?
Inductive Coupling:
the author,
Amal Graafstra,
and his girlfriend,
Jennifer Tomblin,
have matching RFID
implants.
BAN & Monitoring
EEG
Vision
hearing
Heart
monitoring
NETWORK
Blood pressure
Glucose
implant
Handset evolution
Size
Weight
Price
Functionality
Design
1990
Antennas:
2000
• Size reduction: effect on polarisation, bandwidth,
efficiency and manufacturing tolerances
• Reduced ground plane: effect on matching, bandwidth,
patterns and user interaction
• Price reduction: low cost elements
Antennas for mobile terminals
Internal mobile phone
antennas
Antennas for
PCMCIA cards
Customised antennas for
specific applications
Applications
• Mobile phones
• Mobile phones
• GSM modules for customised applications
• GSM modules for customised applications
• PCMCIA
• PCMCIA
• Special terminals
• Special terminals
- Emergency phones
- Emergency phones
- Code bars readers
- Code bars readers
- Credit cards terminals…
- Credit cards terminals…
Effect of the components
•• Limited
Limitedavailable
availablevolume
volume
•• Circuits
Circuitsand
andcomponents
components
•• Antenna:
Antenna:only
onlycomponent
componentwith
withphysical
physical
limitations
for
miniaturisation!
limitations for miniaturisation!
iPoDs and Implants
Future of body centric communications
RFID (Radio Frequency Identification )
System
* Technology for automatic identification of objects
* Application : logistics,security system,animal tracking transportation
and manufcacturing process control
Why are Metamaterials interesting?
z They require combining expertise in the fields of
electrical engineering and materials science.
z Artificial Dielectrics and their Applications:
– Explore Metamaterials and
– Investigate their viability in enhancing antenna
performance.
z Antennas and Metamaterials:
– Size Reduction
– Other Improvements, e.g., bandwidth, directivity
and pattern shape.
– They can make objects dissapear (cloaking)
*Fine print—That’s the promise anyway!!
LET’S BEGIN WITH A LITTLE
HISTORY
HOW DID WE GET STARTED ON THE
DNG STUFF? WHAT WOULD THEY DO FOR
US ONCE WE HAVE THEM?
Engineered media that have a negative
index of refraction ( negative permittivity and
Permeability)
V.G.Veselago, SOV. Phys, 10, 509
1968
The ‘Perfect Lens’
Perfect reconstruction, High Transverse Wave vectors
Imaginary Longitudinal component Evanescent Fields
Realization of Metamaterials
V.G.Veselago, SOV. Phys, 10,
509,1968
•
Metamaterials are artificial materials that
exhibit electromagnetic responses generally
not found in nature.
•
Engineered media that have a negative index
of refraction ( negative permittivity and
permeability )
•
Predicted in 1968 by V.G.Veselago
•
E,H and K form a left-handed system of
vectors
Composite Metamaterial (CMM)
D.R.Smith and S.Schultz, UCSD
Realization (contd.)
Realization of Conventional Metamaterial
Negative ε
• Thin metallic wires are arranged periodically
• Effective permittivity takes negative values below plasma frequency
Negative μ
• An array of split-ring resonators (SRRs) are arranged periodically
( Koray Aydin, Bilkent University, Turkey Sep 6 , 2004 )
Extraction of constitutive effective
parameters from S-parameters for
normal incidence
Effective Parameters
Inversion Method
• Can be applied to both simple and complex structures
• Can use both numerical and experimental data
• S-parameters for metamaterials are more complex
• Ambiguities in the inversion formulas
Equations used in the inversion approach
z
Compute Z:
z
Compute n:
z
(1 + S11 ) 2 − S 212
Z =±
(1 − S11 ) 2 − S 212
( 2 different roots )
-
Compute effective μ
and ε:
(
1
1 − S 112 + S 212
2 S 21
X =
Y=
<= 1
)
e − ink0 d = X ± i 1 − X 2
( 2 different roots )
1
n=−
{[[ln(e −ink0 d )]"+2mπ ] − i[ln(e −ink0 d )]'} (branches with different m)
kod
Conditions used:
Z’ > 0 and
n”<=0, ε”<= 0 and μ” <= 0
Iterative approach to pick n such that n is continuous
ε eff = n / z
μ eff = nz
and
Example 1: 2-D infinite array of dipoles for normal incidence
Z
BC used
X and Y: PBC
Z: PML
Ei, Et and Er are
the contributions
from the zeroth
Floquet mode
measured on the
corresponding X
planes.
Unit cell
Plane of
transmission
Plane of
reflection
Y
Plane wave
source EY
Solutions for all branches ( m=0, -1 and +1) and 2 roots
Determine the solution
by using ref. (1):
(2)
(1)
(1)
(1) By enforcing ε” <0
and μ” <0, only m=0
can be solution.
(2) By enforcing n”<0, the
correct root can be
determined.
Extracted parameters: 2-D infinite array of dipoles
Example 2: 2-D infinite array of split-rings for normal incidence
Z
Unit cell
BC used
X and Y: PBC
Z: PML
Plane of
transmission
Plane of
reflection
X
Y
Plane wave
source EY
Extracted parameters: 2-D infinite array of split-rings
Note: The shaded area represents the non-physical region, where ε” or μ” > 0. In this
region, we choose the branch that best connect n just before and after this band.
Example 3: 2-D infinite array of split-rings + dipoles for normal incidence
Z
Unit cell
BC used
X and Y: PBC
Z: PML
Plane of
transmission
Plane of
reflection
X
Y
Plane wave
source EY
Extracted parameters: 2-D infinite array of split-rings+dipoles (1-layer)
Note: The shaded area represents the non-physical region, where ε” or μ” > 0.
2-D Infinite array of split-rings + dipoles ( 2-layer )
Note: The shaded area represents the non-physical region, where ε” or μ” > 0.
Extracted parameters: 2-D infinite array of split-rings+dipoles (2-layer)
Note: The shaded area represents the non-physical region, where ε” or μ” > 0.
2-D Infinite array of split-rings + dipoles ( 3-layer )
Note: The shaded area represents the non-physical region, where ε” or μ” > 0.
Extracted parameters: 2-D infinite array of split-rings+dipoles (3-layer)
Note: The shaded area represents the non-physical region, where ε” or μ” > 0.
2-D Infinite array of split-rings + dipoles ( 4-layer )
Note: The shaded area represents the non-physical region, where ε” or μ” > 0.
Extracted parameters: 2-D infinite array of split-rings+dipoles (4-layer)
Note: The shaded area represents the non-physical region, where ε” or μ” > 0.
Comparison of effective parameters for 1 to 4-layer split-ring + dipole
Note: The effective parameters for 1-4 layers are almost the same, except that more
resonant peaks can be seen for more layers.
Refraction in DNG Prisms
DNG
DPS
Metamaterial Design using SRRs and Dipoles
w
t
y
L2
L1
z
z
x
Front view
Top view
d
z
g
x
qw
z
Top view of a
metamaterial prism
Le-Wei Li, Hai-Ying Yao, and Wei Xu
National University of Singapore, Kent Ridge, Singapore
Qun Wu
Harbin Institute of Technology, Harbin, China
IWAT’05, March 7, 2005, Singapore
y
x
Simulation Results
z Distribution
of
electric field
component Ez(r,t) in
rectangular linear
around a
metamaterial prism at
f=16.21 GHz
Le-Wei Li, Hai-Ying Yao, and Wei Xu
National University of Singapore, Kent Ridge, Singapore
Qun Wu
Harbin Institute of Technology, Harbin, China
IWAT’05, March 7, 2005, Singapore
Simulation Results
z
Electric field component Ez(r,t) distribution due to a
metamaterial prism
Le-Wei Li, Hai-Ying Yao, and Wei Xu
National University of Singapore, Kent Ridge, Singapore
Qun Wu
Harbin Institute of Technology, Harbin, China
IWAT’05, March 7, 2005, Singapore
Scattering Pattern
z Distribution
of
electric field
component Ez(r,t)
in polar plot due to
a metamaterial
prism at f=16.21
GHz
Le-Wei Li, Hai-Ying Yao, and Wei Xu
National University of Singapore, Kent Ridge, Singapore
Qun Wu
Harbin Institute of Technology, Harbin, China
IWAT’05, March 7, 2005, Singapore
Negative Refraction in a Slab
DNG
SLAB
Comprising
of Periodic
Structures
Plane wave
θ ??
EBG Array Settings: Oblique incidence (TMz)
FDTD Computational domain
Phsyical size: 85.5 mm x 85 mm x 67 mm
Cell number: 680 x 684 x 536 = 2.5 x 108 cells
λ = wavelength
at 15.0 GHz
22 mm = 1.1 λ
Guassian beam
θ = 30o
85 mm = 4.3 λ
24 mm = 1.2 λ
85.5 mm = 4.3 λ Array settings:
Ele. Separation: 2.25 mm x 5 mm x 4 m
Ele. Separation in λ: 0.1125 x 0.25 x 0.20
Total number: 38 x 17 x 6 = 3876
Total number falls within beam width = 34 ( X: 10, Y
Vertical Field Distribution
at 14.4 GHz
P2
P1
Array ( 6 layers )
P4
P4: YZ Plane
Free space
Dielectric Slab
EBG Array
P4: Transmission region
Free space
Dielectric Slab
EBG Array
Transverse Field distribution P4 and P5 at
15.0 GHz
Free space
Dielectric slab
P4: ~2/3 wavelength behind the
array
P5: ~1 wavelength behind the array
EBG Array
Transverse Field distribution P2 and P3 at
16.0 GHz
P2: Right behind the slab/array
Free space
Dielectric slab
P3: ~1/3 wavelength behind the array
EBG Array
Transverse Field distribution P4 and P5 at
17.5 GHz
Free space
Dielectric slab
P4: ~2/3 wavelength behind the array
P5: ~1 wavelength behind the array
EBG Array
Vertical Field Distribution
at 15.6 GHz
P2
P1
Array ( 6 layers )
P4: YZ Plane
Free space
Dielectric Slab
P4
EBG Array
P4: Transmission region
Free space
Dielectric Slab
EBG Array
SINGLE & MULTIPLE LAYER SRR
Field Planes
Ring
Ring Dimensions
Side length – 3mm
Thickness - 0.25mm
Gap - 0.5mm
Waveguide Dimensions
X-band waveguide
Width – 19.25mm
Height – 10.625mm
z
x
y
Voltage Measurement
points
Terminated by PML walls
to avoid reflections
The SRR was placed vertically with the gap-bearing side parallel to the
direction of propagation.
Field Distributions Confirm the
Resonant Permeability Behavior
Amplitude
Before the
resonance
Phase
Amplitude
Phase
After the
resonance
SRR Design : Perpendicular Orientation
Field Planes
Ring
Ring Dimensions
Side length – 3mm
Thickness - 0.25mm
Gap - 0.5mm
Waveguide Dimensions
X-band waveguide
Width – 19.25mm
Height – 10.625mm
z
x
y
Voltage Measurement
points
Terminated by PML walls
to avoid reflections
The SRR was placed vertically with the gap-bearing side perpendicular to
the direction of propagation.
S-parameters and Effective
Parameters: Parallel Orientation
• Comparison of real parts of
effective permittivity and
effective permeability
• Comparison of reflection and
transmission coefficients obtained
from measurements and
simulations (Dimensions Scaled)
Perpendicular Orientation - Results
Comparison of real parts of
effective permittivity and effective
permeability
Comparison of reflection and
transmission coefficients obtained
from measurements and simulations
(Dimensions scaled)
Composite Unit Cell - Results
• Comparison of reflection coefficients
obtained from simulations for the
three cases
• Comparison of real parts of
effective permittivity and
effective permeability
Verification
Confirmation of Backward Wave Propagation
Distance d of the
points from the
source
d
Source
Phase of the field
measured at three
different points along
the waveguide
inside the DNG unit
cell
z
y
Increase in phase ( phase advance) for points away from the source in the
frequency range where the effective parameters are simultaneously
negative.
Simulation and Field Analysis
x
y
BC-SRRS
Waveguide
Coaxial feed
Ez in XY-plane
8.4 GHz
37600
8.7 GHz
74000
8.9 GHz
y
Hz in YZ-plane
62000
8.8 GHz
76300
79400
• SRRs are coupled as seen from
the magnitude and phase
distributions of the E and H fields
• The axial magnetic moment does
not exist and so cannot cause
negative permeability.
z
9.1 GHz
x
68700
Pass Band below cutoff
8.6 GHz
y
8.7Ghz
• Wave tunneling might be due to a
resonance wave propagation along
the SRR chain
K – Band Wave Guide
Pass Band below Cutoff
Waveguide Dimensions
Width – 10.66mm
Height – 4.2mm
Cut off – 14.07GHz
Ring Dimensions
Side length – 1.7mm
Thickness - 0.25mm
Gap - 0.48mm
Cut Off
Magnitude and Phase of Ex near
the SRR
Magnitude Phase
z
Regular Half-wavelength Resonance
of the SRR ( Negative Permeability)
Transmission Coefficient
y
Field Distributions
Ex (13.65GHz)
Ex(13.95GHz)
• Components of E and
H fields normal to the
SRR plane
• Magnitude of the fields
is more than 3 times
higher than that at other
frequencies
9.97e+005
4.89e+005
z
1.03e+003
y
Hx(13.65GHz)
Half wavelength Resonance
3.07e+002
Hx(13.95Ghz)
Full wavelength Resonance
• Separation ~ 0.35Ghz
and the fact that the
Half-wavelength
resonance occurs at two
frequencies indicates that
a slow wave mode
propagates through the
SRR waveguide below
cutoff
z Next
3 Slides are courtesy of Prof. Hossein
Mossallei of Northeastern University
Electromagnetic Communication Lab
1 layer and 3 Layer Periodic Array of Spheres
z
y
3-Layer with h=2.5 and d=1.5 cm
x
Diameter = 1 cm
εr=40
h=2.5 cm
d
1-Layer
Tripod FSS – Layered Structures
2 of 2-Layer
2-Layer
D=1 mm
d=0.02 mm
L1
L2
240 o flare angle
L1 = 0.40 mm
L 2 = 0.48 mm
Tz
T y = 1.40 mm
T z = 2.44 mm
110.0
110.0
110.0
normal incidence
o
TE at 30
o
TM at 30
100.0
% of Power Reflected
90.0
% of Power Reflected
80.0
70.0
60.0
100.0
100.0
90.0
90.0
80.0
80.0
70.0
70.0
% of Power Reflected
Ty
60.0
50.0
40.0
normal incidence
o
TE at 30
o
TM at 30
60.0
50.0
40.0
50.0
30.0
30.0
40.0
20.0
normal incidence
o
TE at 30
o
TM at 30
30.0
10.0
20.0
10.0
20.0
0.0
0.0
10.0
20.0
40.0
60.0
80.0
100.0
120.0
frequency (GHz)
140.0
160.0
180.0
200.0
0.0
0.0
20.0
40.0
60.0
80.0
100.0 120.0 140.0
frequency (GHz)
0.0
0.0
20.0
40.0
60.0
80.0
100.0 120.0
frequency (GHz)
140.0
160.0 180.0
200.0
160.0 180.0
200.0
Sphere Dielectric and Coupling Performance
εr=20
z
εr=10
y
x
160 nm
520 nm
260 nm
εr
H-Field in y-x plane
Coupling and Resonance Behavior
Electric Dipole
Magnetic Dipole
Normal Mode
Magnetic Dipole
Electric Dipole
Reverse Mode
TIME TO RAISE A FEW ??
THE PERFECT LENS?
Refraction in DNG Prisms
DNG
DPS
Equivalent Medium Approach
It is a Common practice to replace an artificial dielectric with its equivalent ε and μ
perform an analysis of composite structures (antenna + medium) using the equivalent
medium.
But this can lead to significant errors and wrong conclusions
R
.
.
.
Single layer
. . .
. . .
. . .
T
Multiple layers
Floquet
harmonics
Exit
angle?
Negative Retraction in a Slab
θ ??
DNG
SLAB
Plane wave
Imaging with DNG Lens
source
0
I
Z
DNG LENS
Field distribution along z in the RHS of Lens
Field
Distribution
or ?
0
I
Z
Field
Distribution
0
7
Z
Question?
DNG
Images?
Lens
Can we resolve two longitudinally-spaced sources
with a DNG lens?
NEXT ?
SMALL ANTENNAS WITH VERY HIGH
DIRECTIVITIES?
ENG
DPS
Performance Enhancement of Small
Antennas
Thin shell,
Radius << λ
Big Q??
Small Antenna
(length << λ)
Can we violate
Chu limit?
Artificial Magneto-Dielectric Substrates
Performance Enhancement of Wire and Patch Antennas Using Artificial Materials
Pekka Ikonen(1), Stanislav Maslovski(1), Kostantin Rozanov(2), Murat Ermutlu(3), and Sergei Tretyakov(1)
(1)Radio Laboratory / SMARAD Center of Excellence Helsinki University of Technology
(2)Institute for Theoretical and Applied Electrodynamics, Russian Academy of Sciences, Moscow, Russia
(3)Nokia Networks, Finland
Transmission Line Approach
z
Based on Transmission Line (TL)
circuit models:
z
z LH-TL
Clockwise from top right:
RH-TL
– Regular
A single microstrip
unit-cell design.
line
– Inductance/Capacitance interchanged
– Lowpass
A two unit-cell
in nature
design.
– Series/Parallel arrangements inverted
– Highpass in nature
– Fabricated single unit-cell BW
TL.
Parallel-Plate
Capacitors
1.2mm
Multilayered
Loop
Inductors
Loading a MPA
z
Microstrip Patch Antenna
(MPA):
Normally λ/2 a side.
– TL structure loads sides.
– Size reductions.
–
z
Antennas tested:
7.55 GHz λ/4 (69% area
savings).
– 485 MHz λ/6 (87% area
savings).
– 348 MHz λ/8 (93% area
savings).
–
Size-Reduction of MPA:
Width=2.25 ”
Length=0.125”
Patch
3.5" = 0.4λ@ f = 430 MHz
via to ground plane
Y
X
Loading Strip
Height = 0.01875” = 18.75 mils
via = 0.04375” = 43.75 mils ε r = 9
Z
Y
Ground Plane
X
(b)
(a)
via
Probe feed
loading strip
X
Y
(a) Ez field distribution between patch and ground @ f=430 MHz
(b) Ex field distribution between patch and ground @ f=430 MHz
(c) Ey field distribution between patch and ground @ f=430 MHz
(c)
z
ε r 2 ≈ 23.8
Partially filled Cavity
ε r 2k y 2
Y1 =
tan( k y 2 h )
ε r 1k y1
PMC
(3)
ε r3
d
a
ε r1 PMC
PMC
Y 2 = γ (ε r 2 )
(1)
εr2
b
(2)
PMCPMC
PMC
h
y
L
a’
x
Simulation results based on theoretically
calculated effective dielectric constant:
Directivity Enhancement of a Class of Patch
Antennas using Metamaterial Superstrates
Motivation
◈ In the past, array antennas had been widely used for applications
requiring high directive antennas.
◈ However, array antennas require a complex feed network, and it
makes difficulty in fabrication of array antennas and cause losses.
◈ A simple way to obtain high directivity with one or a few radiators
is necessary. Æ Metamaterial superstrates
High Directivity
Array and
complex
feed
network
Beam
Superstrate
Patch
Candidates for Metamaterial Superstrates
◈ Periodic structures such as FSSs and EBGs act as spatial angular
filters with transmission and reflection pass and stop bands, and
can be used to enhance directivity of a class of antennas being
placed above them.
Stacked
dielectric layer
◈
Dielectric rod
EBG
FSS
Woodpile EBG
Two approaches for the analysis of antennas with
metamaterial superstrates
1.
Fabry-Perot Cavity (FPC) AntennaÆ Partially Reflecting Surface (PRS)
2.
Leaky Wave Antenna
Fabrication and Measurement Results of the 7×28
Strip Dipole FSS Composite
εr=2.2,
t=20mil
0
E-plane(12.5GHz)
H-plane(12.5GHz)
E-plane(simul)
H-plane(simul)
-5
-10
1.00 cm
power(dB)
-15
-20
-25
-30
-35
-40
-80
11.76cm
-60
-40
-20
0
20
40
60
80
angle(degree)
22
simulation
measurement
20
Gain(dB)
18
16
14
9.66cm
12
L1=1.33cm,
dl=1.0cm
10
11.5
12
12.5
Frequency(GHz)
FSS superstrate printed on a commercial
Measured Maximum
available dielectric material
Directivity: 19.5dB
13
13.5
20×10 Thin FSS Superstrate
Fabrication and Measurement Results of the
20×10 Thin FSS Composite (1)
Two FSS layer are etched in same
substrate whose thickness is only
2.0828 mm
The design parameter values
< back view >
< top view >
εr = 2.2,
t = 2.0828 mm
FSS array size: 10 × 20
a = 12, b = 6
dl_l = 8.7, dl_u = 11.2
dw_l =1, dw_u = 4
h = 16, Lg=2.0828
h = 13
< side view >
8.41 and 11.67 GHz
Must we use DNG superstrate and other metamaterials
and look for focusing effects for directivity enhancement?
Metamaterials with frozen modes and
other Special Characteristics
DNG
Microstrip
patch
Ground plane
Ground plane
DNG
Ground plane
Microstrip
patch
FSS
Ground plane
Microstrip
patch
Q. Can we achieve higher directivity than is possible for a uniformly
illuminated aperture of the same size as that of the antenna + superstrate
composite?
TE mode E-field
when θ=1, φ=90
TM mode E-field
when θ=1, φ=0
S11 ~ -1.4 dB at 13 GHz
Phase ~ 360 deg at 13 GHz
S21 ~ -6 dB at 13 GHz
Phase ~ -90 deg at 13 GHz
find any
resonant
mode at 13
GHz but
reflection
phase
Can’t
Dual-layer simulation
Single-layer (red line) dipole compare to dual-layer (blue line)
L = 1.4
L = 1.3
L = 1.2
Geometry of a fabricated dipole strip FSS
composite and its unit cell.
Comparison of the simulated and measurement results: (a)
directivity and (b) radiation pattern
EBG SUBSTRATES
DO THEY ENHANCE ANTENNA
PERFORMANCE?
REF: EuCAP’06 PAPER BY LIVERPOOL U
CONVENTIONAL MSA
SLOT ANENNA ABOVE HIS
RETURN LOSS CHARACTERISTICS OF
ANTENNA ABOVE HIS
ALTERNATIVE TO VESELAGO
LENS?
Source
plane
Image
plane
Imaging
Device
Distribution of electric field
a) near the front interface
b) near the back interface
Near field scan results
Distribution of electrical field at the source and image planes.
Confirmation of λ/15 resolution and 18% bandwidth reported!
P.A. Belov, Y. Hao, S. Sudhakaran, “Subwavelength microwave imaging using an array of parallel
conducting wires as a lens”, Phys. Rev. B, vol. 73, 033108, 2006.
Intensity distribution
a) near the front interface
b) near the back interface
Resolution is λ/15!
P.A. Belov, Y. Hao, S. Sudhakaran, “Subwavelength microwave imaging using an
array of parallel conducting wires as a lens”, Phys. Rev. B, vol. 73, 033108, 2006.
AMC Ground Designs
Response of AMC Ground
AMC Ground
Antenna over AMC Ground
SUMMARY Q’S
z
z
z
z
Q1.
DNG’S ARE INTERESING CONCEPTUALLY, BUT IS
THIS LENS BUSINESS REALY PRACTICAL? IT
DOESN’T ACTUALLY WORK LIKE A
CONVNTIONAL OPTICAL LENS; THE MATERIAL IS
NOT ISOTROPIC; AND, LOSSES AND BANDWIDTH
CAN BE PROBLEMS.
Q2.
OK, SO EVEN IF WE PUT THE LENS BUSINESS
ASIDE, HOW ABOUT THEIR USE AS SUBSTRATES,
SUPERSTRATES ABD SHELL COVERS FOR SMALL
ANTENNAS? SHOULD WE ONLY LOOK FOR DNG’S
FOR THESE APPLICATIONS?
MORE QUESTIONS
z
z
z
z
z
Q3.
CAN WE GET MORE DIRECIVITY FROM A SMALL
ANTENNA COMPOSITE (ANTENNA +
SUPERSTRATE) BY USING METAMAERIALS, THAN
IS POSSIBLE TO REALIZE FROM THE APERTURE
SIZE OF THE COMPOSITE?
Q4.
CAN WE GET GOOD BACKLOBE SUPPRESSION
FROM A GROUNDPLNE, WHOSE SIZE IS
COMPARABLE TO THAT OF THE ANTENNA (∼λ/2),
BY USING METAMATERIALS?
SHOULD ALL MANNER OF IMAGING SYSEMS BE
LABELED AS LENSES?
A FEW MORE
z
z
Q5.
DO THE EFFECTIVE PARAMETERS REMAINUNCHANGED
WHEN WE VARY THE THCKNESS OF THE METAMATERIAL
SLAB, OR CHANGE THE INCIDENT ANGLE?
z
Q6.
FOR SMALL ANTENNA/SUPESTRATE COMPOSITES,
SHOULD WE BE LOOKING AT THE SIZE OF THE
ANTENNA OR THA OF THE COMPOSITE WHEN
COMPARING DIRECTIVITIES?
z
z
Q7.
z
IS THERE A SPECIFIC ADVANTAGE TO BE GAINED
IN USING EBG’S WITH SMALL PERIODICIIES
WHOSE CELL SIZE IS MUCH SMALLER THAN A
WAVELENGTH?
BIG QUESTION(S)??
z SO,
WHERE DO WE GO FROM HERE?
z HOW DO WE REALIZE LOW LOSS,
ISOTROPIC, ESSENTIALLY NONDISPERSIVE METAMATERIALS THAT
ARE LOW COST AND CAN BE
INTEGRATED WITH SMALL ANTENNAS
TO IMPROVE THEIR FUNCTIONALIY
AND PEFORMANCE?
Resonator Array structures for
metamaterials?
z
z
z
Higher Frequencies
pushing into the THz
range
Spherical resonators
instead of cylindrical
resonators
Free space optical
testing.
1 mm diameter silica spheres.
Fabricated by Amanda Baker
W0RTH A LOOK?
COURTESY OF ELENA SEMOUCHKINA (PENN STATE)
A WORD ABOUT SIMULATION
Antenna-metamaterial composites require
heavy duty computing power to model
(Note: We routinely simulate upward of billionunknown-category problems)
Resonator Array structures for
metamaterials?
• Higher Frequencies
pushing into the THz
range
• Spherical resonators
instead of cylindrical
resonators
• Free space optical
testing.
1 mm diameter silica spheres.
Fabricated by Amanda Baker