natural and metamaterial low-profile antennas with ... nakano.pdf · with emphasis on realization...

Natural and Metamaterial Low-profile Antennas

with Emphasis on Realization of Wideband Characteristics

- Antenna Height from l/4 to l/100 -

H. NAKANO

Hosei University

Tokyo

Japan

1

Recent developments in communication systems, e.g.,

Mobile, Digital TV, and Satellite Communication Systems, require

Antennas

with

Dual-, Multi-, Moderately Wide-, and Extremely Wide-

Band Operation

-:: categorized as either

Natural Antenna or Metamaterial (MTM) Antenna

Natural Antenna / EM Property Found in Nature

(Right-Handed Property)

MTM Antenna / EM Property not Existing in Nature

(Left-Handed Property)

Choice of either a Natural or an MTM Antenna depends on

the requirements of the target communications system.

2

TALK PRESENTATION

recent progress in some

Natural and MTM Antennas.

Low-Profile Structure

realizing

Moderately wideband characteristics

Wideband characteristics

Extremely wideband characteristics

Key Words ::

Low Profile Structure

Wideband Characteristics

3

Section I Introduction

Section II Natural TW antennas

Out line

Section III Metamaterial TW antennas

Section IV Remarks

II-A Low-profile, moderately wideband helical antenna

II-B Extremely wideband fan-shaped antennas

for a base-station and a portable handset

II-C Low-profile, extremely wideband *BOR-SPR antenna

for a base-station antenna

*Body of Revolution with a Shorted Parasitic Ring

II-D Low-profile, wideband rhombic grid array antenna

for frequency beam-scanning

III-A History of the antenna height reduction of a spiral antenna

III-B Extremely low-profile, moderately wideband spiral antenna for counter CP radiation

4



Out line


Section IV Remarks











5

Practical Antenna Arms / / a Finite Length,

Current : composed of *

an out-going current & an in-coming current

The in-coming current

changes the situation at the antenna input.

~ changes the antenna input impedance in response to

the antenna shape & operating frequency.

in-coming current

out-going current

antenna input

(Current Distribution along Antenna Arms)*

6

.. Reduce the In-coming Current &

.. Use Only the

Out-Going Traveling Wave (TW) Current to Realize Wide Band Antennas

-: categorized as either

Positive-b TW current

or

Negative-b TW current.

Antenna based on a positive-b TW current : defined as*

Antenna based on a negative-b TW current : defined as

Metamaterial (TW) Antenna

Natural (TW) Antenna*

7

- - A positive-b current flows from F’ to T’

A Phase-Lag Based on a positive-b Current

Forward Radiation*

Forward Radiation

*Example of a Natural TW Antenna*

8

x

z

- - Capacitances and Inductances ::

inserted into a microstrip line*

*Example of a MTM TW Antenna

G.P.( )8

CL CL

LL

E

E

z

x0 -10 -20 [dB]

z

x0 -10 -20 [dB]

z

x0 -10 -20 [dB]

2.5 GHz 2.8 GHz 3.0 GHz

Backward Radiation

A negative-b current flows from the left to the right.

A Phase-Progress Based on a Negative-b Current

Backward Radiation

9



Out line


Section IV Remarks











10

FINDING

Current /

two distinct regions

C-current region* &

S-current region*

Helical Antenna

Feed Axial Mode

GP

11

Axial Mode Axial Mode

.. Remove the S-current region* &

.. use only the C-current region

for CP radiation

-/ a decaying TW current

along the helical arm of

~ two turns* *

2 turns

~ an antenna height of

0.19 wavelength

above the GP

Feed Axial Mode

GP

12

*Application of Low-Profile Helical Element

Each element : arrayed on a cavity

Vertical line of the helix : inserted into a cavity* &

excited by a traveling EM wave*

Aperture Efficiency :

extremely high and approx. 90%.

Side view of a cavity

Aperture

Efficiency

~ 90% Circular cavity

Phase :

controlled by rotating the element

around its axis.

Amplitude :

controlled by the vertical length

inserted into the cavity.

13

ARRAY /: used as

Indoor Broadcasting Satellite Receiving Antenna

Designed by Nakano Lab

Produced by Yagi Antenna Co.

Designed by Nakano Lab

Produced by TDK Co.

Dia. = 27.8 cm

G = 29.5 dBi,

/ Dia. = 33 cm

G = 31.7 dBi,

Aperture efficiency of h = 88%

Array applications

14

Primary feed /a two-layer structure.

X band (8.1-8.9 GHz, BW = 9.4%).

S band (2.1-2.6 GHz, BW = 21.3%)

Helical elements: plated with Gold

http://veraserver.mtk.nao.ac.jp/restricted/status05

.pdf (Japanese)

Cassegrain reflector /

a main dish of diameter of 20 m * &

a sub-dish of diameter of 2.6 m.

Focal length of main dish : 6 m. *

hu

X band

S band

Designed by Nakano Lab with

The National Astronomical Observatory of Japan

Designed by Nakano Lab with NAOJ

15

= 0oplane

0 -10 -20 (dB)90

o

x

60o 60

o

30o 30

o

0o

90o y

E

theoretical｛z z

E

60o 60

o

30o 30

o

0o

= 90oplane

0 -10 -20 (dB)

f=12.45GHz

Radiation pattern

E sence and E sence

f = 2.35 GHz ER

EL

z

y

xx

z

y Symbol Value

DHLX 41.38 mm 0.3241l2.35

n 3.1 turns

a 4º

r 0.5 mm 3.91710-3

l2.35

HCAV 495 mm 3.8775l2.35

DCAV 36 mm 0.282l2.35

Scir 109 mm 0.8538l2.35

Srad 104 mm 0.8147l2.35

* l2.35 127.66 mm

A beam width of 22º for a 7-dB reduced field intensity criterion is realized,

meeting the requirement for both of the feed antennas.

S Band

= 0oplane

0 -10 -20 (dB)90

o

x

60o 60

o

30o 30

o

0o

90o y

E

theoretical｛z z

E

60o 60

o

30o 30

o

0o

= 90oplane

0 -10 -20 (dB)

f=12.45GHz

Radiation pattern

E sence and E sence

f = 8.55 GHz

z

y

x

z

y

x

Symbol Value

DHLX 11.169 mm 0.3183l8.55

n 2.8 turns

a 4º

r 0.2 mm 5.710-3

l8.55

HCAV 142 mm 4.047l8.55

DCAV 9.7 mm 0.27645l8.55

Scir 29.4 mm 0.8379l8.55

Srad 28.1mm 0.8009l8.55

* l8.55 35.294 mm

X Band

The same beam width is realized.

Radiation Pattern

16

*Helical antenna array for a “BepiColombo”

Presented by

JAXA and

NEC-TOSHIBA Space System

17



Out line


Section IV Remarks











18

II. Natural Wideband antennas

II - B. CROSS-FAN and CROSS-FAN-S

8

8 8

8GP

- / Only an Out-going Current

IF: Conical Arm: Infinitely Long &

Ground Plane : of Infinite Extent

Input impedance : Frequency-Independent*

*Conducting Conical Antenna

Practical Structure

//The Conical Arm Cannot Be Infinitely Long!

19

II Natural Wideband Antennas.

II B CROSS-FAN and CROSS-FAN-S

Practical

Truncated

Conical Antenna

GP

No More: Inherent Frequency-Independent Characteristics

// .. Expect Wideband Characteristics

- Partially Retains the Original Structure

20

~

x

y

z

.. FABRICATION

Low-Profile Antenna

- - A Pair of Fan-Shaped Plates

Intersect at Right Angles*

GP

Truncated

Conical Antenna*

Modification from a Truncated Conical to

A CROSS-FAN Antenna



21

Note: VSWR : less than two at frequencies above 2.1 GHz*.

Antenna Height : 0.3 Wavelength at 2.1 GHz.

Radiation : Omnidirectional around the antenna axis (z-axis).

frequency [GHz]

1 2 3 4 5 6 7 8 9 10 11

1

2

3

4

5

6

7

VS

WR

Figure 4

CROSS-FANCROSS-FAN

x

z

P(xP, 0, z

P)

Q(0, 0, zQ)

y



*Frequency Response of the VSWR of the Cross-Fan Antenna

Antenna Height : 0.3 Wavelength at 2.1 GHz

22

Cross-fan : often required to have a stop band within the VSWR band

Introducing slots* into the fan-shaped plates : recommended.

This antenna : designated as the CROSS-FAN-SLOT.



Technique for Stop-Band Generation in order to prevent the reception of interference from nearby devices

CROSS-FAN-SLOT

Slot Slot

Slot

Requirement of Stop Band

>

23

Slot Length Lslot : ~ one-quarter wavelength at fstop.


II B CROSS-FAN and CROSS-FAN-S *VSWR of the CROSS-FAN-SLOT

As Slot Length Lslot

Stop-Band Center Freq. fstop*

1 2 3 4 5 6 7 8 9 10 11

1

3

5

7

9

VS

WR

freque nc y [GHz ]

fs top

A Stop Band : * around 5.2 GHz

24

y

x

Ly

S

Q

ground plate

o

S

Lx

(a)Fan-shaped plate antenna CROSS-FAN /: Used as

a Base Station Antenna

.. MODIIFICATION CROSS-FAN for a Portable Handset

~

x

y

z

Base Station Antenna >>> Portable Handset Antenna

- REQUIREMENT Card-type Structure

.. REDUCTION Two fan-shaped plates to one plate ** &

.. MAKE Antenna Height Small - : Fan-shaped plate antenna

25

Ly

Lx

y

x

Ly

S

Q

ground plate

o

S

Lx

(a)

2ar

ro

Q

P1(x1,y1)

P2

P3

P0

S = 2r

r

FD

y

x

(b)

y

ground plate

2t

r z

(c)

* Detail of fan-shaped plate Antenna

Radiation Element & Ground plane lie in the same plane.

Radiation Element : sandwiched by dielectric substrates of r*.

Bandwidth : optimized by the inner angle 2a. *

Side Length S : ~1 cm. *

Ground Plane / a side length of 3 cm

r ~1 cm 3 cm

Radiation Element

GP

Side View

GP

26

*Frequency response of the VSWR

2a = 120 degrees.

(r, 2t, S) = (20, 1 mm, 10.87 mm),

(Lx, Ly) = (30 mm, 30 mm),

r = 5.44 mm

Note: VSWR < 2 above 2.75 GHz.

Antenna Height : 0.09l at 2.75 GHz.

Ground Plane / a side length of 3 cm

2ar

ro

Q

P1(x1,y1)

P2

P3

P0

S = 2r

r

FD

y

x

(b)

~1 cm

2 3 4 5 6 7 8 9 10 111

3

5

7

9

10

r = 20

2a = 120o

theo.

theo.

exp.{r = 1

VS

WR

frequency [GHz]

2a

( no dielectric layers

for the FASH)

27

- : Installed in a handset device. *

- : Sandwiched by dielectric substrates

Substrate /

an area of ~1 cm x 1 cm.

The substrate has an area of 1 cm by 1 cm.

The antennas installed inside a handset device.

Installation of a Fan-Shaped Antenna *

28

Designed by Nakano Lab.

Produced by Mitsumi Co.



Out line


Section IV Remarks











29

~

x

y

z

Antenna Height

H = 0.3l

CROSS-FAN

z

H c o a x .

GP

BOR-SPR Body of Revolution with

a Shorted Parasitic Ring

Lower Base Station Antenna

H = 0.07l

BASE STATION ANTENNA II II Natural Wideband Antennas.

IIC BOR-SPR

30

*BOR-SPR Antenna : composed of

a conducting body of revolution (feed section) *

& a parasitic conducting ring* :

shorted to the ground plane through conducting pins *.

Antenna Height : extremely small*: 0.07 wavelength.


II C BOR-SPR BOR-SPR Base-station Antenna

BOR

parasitic ring

conducting pin

H = 0.07l

z

H

c o a x .

GP

31

Design of BOR-SPA II Natural Wideband Antennas.

II C BOR-SPR

BOR

Parasitic ring

H

.. Replace the feed section by a BOR.

h

c o a x .

G P

.. Cut a ring slot

H

2 x 1

D i n , r i n g

Rin : low < 50

Xin : 0

H = 0.07l

Microstrip patch

H

D p a t c h

D G P

Rin : low < 50

Xin : inductive

~

.. Add four conducting pins.

Rin : 50

Xin : 0

32

First Step : to analyze the input impedance for a low-profile patch

Fig. 1(1/2)

H

Dpatch

DGP

Rin < 50 ohms

Xin : inductive

Note:

There is a frequency region where

the input reactance Xin is highly inductive.

2 . 5 3 . 0 3 . 5 4 . 0 4 . 5 5 . 0 - 1 0 0

0

1 0 0

2 0 0

3 0 0

4 0 0

f r e q u e n c y [ G H z ]

R i n

H = 1 0 m m

D p a t c h = 4 0 m m

D G P = 1 3 6 . 7 m m

X i n

Z i n

[ W

] GP dia. ~ 14 cm

Patch dia. ~ 4 cm

Antenna height H = 1 cm *

Design Process

33

Second step : To make the input reactance Xin zero

by adding a capacitive component.

: performed by cutting

a ring slot into the original patch.*

The slot forms a capacitance.

The original patch : divided into two regions,

parasitic ring region* & small patch island*

Rin : low < 50

Xin : 0

patch island

parasitic ring

H

2x1

Din, ring

Slot

2.5 3.0 3.5 4.0 4.5 5.0-100

0

100

200

300

400

frequency [GHz]

Rin

H = 10 mm

2x1 = 6.7 mm

Di n , r i n g

= 20 mm

Xin

Zin [

W]

3.6 GHz

34

Third Step :To increase the input resistance Rin.

: achieved by increasing the antenna volume.

: performed by adding conducting pins & short them to the ground plane*.

2 4 6 8 1 0 1 2 1 4 1 6 1

2

3

4

5

6

7

f r e q u e n c y [ G H z ]

V S

W R

Rin : increased to 50 ohms

Xin : 0

~

conducting pin

30%


IIC BOR-SPR

35

Final Step : To further increase the frequency BW.

Antenna: excited by a central feed pin *

Central feed pin : replaced by a conducting body of revolution.*

Generating line of the BOR : defined by an exponential function.

H

Dpatch

DGP

H

2x1

Din, ring

~

Parasitic ring conducting pin H = 0.07l z

H

c o a x .

G P

BOR

30% BW

Excited by a Central Feed Pin


IIC BOR-SPR

36

* Frequency response of the VSWR for the BOR-SPR.

An extremely-wide frequency-band of

147% *

Note: The radiation :

omnidirectional around the z-axis.

1 3 5 7 9 11 13 151

2

3

4

5

6

7

frequency [GHz]

{

VS

WR

theo.exp.

Np i n

= 4

2x1 = 6.7 mm

H = 10 mm

z

H

c o a x .

GP

H = 0.07l

rpatch = 0.13l

147% BW

BOR-SPR

Body of Revolution with

Shorted Parasitic Ring 37

BOR-CROSS is installed on the ceiling of a building.

*Installation example

of BOR-CROSS*

Designed by Nakano Lab.

Produced by Yagi Antenna Co.


IIC BOR-SPR

38



Out line


Section IV Remarks











39

*Conventional Grid Array Antenna (GAA)

II Natural antennas

IID Rhombic grid array antenna

x

y

Ly

LxAir

G.P.

H

F T

z

GAA : excited from its edge*

- creates a tilted beam* *Beam direction*

/ a frequency-scanning function.

5 6 7 8 9-30

-15

0

15

30

45

60

Be

am

dir

ec

tio

n

(d

eg

)

Frequency (GHz)

*Beam Direction

as a function of frequency.

Feed Point F

Antenna height H = 2.5 mm

= 0.05l6

= 0.05l6

40

The gain should be constant

across the wide frequency band to be used for beam scanning.

Ga

in (

dB

i)

Frequency (GHz)

5 6 7 8 90

5

10

15

20

25

30

x

y

Ly

LxAir

G.P.

H

F T

z

?? Gain of the conventional GAA ??

?Desirable Gain Behavior?

41

As one solution to this issue*,

.. Propose a New Grid Array Antenna*

Conventional Proposed

-: Rhombic GAA

II Natural antennas


42

Proposed RGAA :

An extension of the conventional GAA.

Radiation Elements :: bent with bend angle 2a *

forming numerous rhombic cells.*

The conventional GAA : a special case , - - the bend angle : 180 degs.

II Natural antennas


x

y

Lx

Lx

Ly

Ly

2Ls

2Ls

2a

F'T'

r

r2

Conventional

GAA

2a = 180o

43

Note: -/ a constant gain across a wide frequency-band. *

the gain for the conventional GAA using a red dotted line*

: clear that the gain for beam scanning is improved.

*Gain for a RGAA -- bend angle of 2a = 120o.*

II Natural antennas


2a = 120o

Ga

in (

dB

i)

Frequency (GHz)

3-dB reduced gain

bandwidth

5 6 7 8 910

15

20

25

2a = 180o

Ga

in (

dB

i)

Frequency (GHz)

5 6 7 8 910

15

20

25x

y

Lx

Lx

Ly

Ly

2Ls

2Ls

2a

F'T'

r

r2

Constant Gain

across a wide frequency band

44

* Beam Direction for Bend Angle 2a = 120o. Note: the beam direction increases linearly with an increasing frequency.

.. Representative radiation patterns at 6 GHz* and 7.7 GHz *

2a = 120o

Be

am

Dir

ec

tio

n

(d

eg

)

Frequency (GHz)

3-dB reduced gain

bandwidth

5 6 7 8 9-30

-15

0

15

30

45

60

II Natural antennas


Details of this work

H. Nakano, Y.Iitsuka, J. Yamauchi, “Rhombic grid array antenna,”

in IEEE Trans. AP, No.5, 2013 (in press)

27% (6 -7.85 GHz)

0o

30o

60o

90o

90o

60o

30o

-10 -20 (dB)x

z

7.7 GHz

0o

30o

60o

90o

90o

60o

30o

-10 -20 (dB)x

z

6 GHz

45

F’

GAA: ~2.28l 6 x 5.2l 6

GP : 150 mm 325 mm

= 3l 6 6.5l 6



Out line


Section IV Remarks











46

~

Unidirectional CP wave

Bidirectional

Circularly polarized (CP) wave

Conducting plate

Frontward

Backward

~

Frontward

Spiral Antenna III MTM Antennas

IIIA History

47

x y

z

~

z

y

x

, t t F 1 F 2

r s

～～

h

z

y

L

F D

r s

~:: Two Techniques to overcome ::~

1st technique_ to place an absorbing ring-shaped strip*

Absorbing Ring-Shaped Strip behind the outermost arm area

Side view

Perspective view

Exploded view

First Technique

48

: to replace the conducting plate by an EBG reflector *

l/10

Antenna Height

Second Technique

EBG

z

y

x

EBG

Spiral

EBG

Side view

Perspective view

III MTM Antennas

IIIA History

49

Zin becomes constant when the conducting plate is replaced by an EBG reflector.

PEC SPA R i n

X i n

Frequency GHz

Z i n

[ W

]

5 . 4 6 . 0 6 . 6 7 . 2 7 . 8 - 4 0 0

- 2 0 0

0

2 0 0

4 0 0

6 0 0

PEC spiral (h = 0.1l6)

.. / Effect of an EBG-Reflector on Zin

EBG SPA

EBG spiral (h = 0.1l6)

EBG

z

y

x

III MTM Antennas

IIIA History

50

Q

Antenna Height

Is it possible to

further reduce the height of

a spiral antenna from l/10?

51



Out line


Section IV Remarks











52

spiral

l/4

~

conducting reflector

- - An antenna height of approximately l/100

.. CONSIDERATION

Further Antenna Height Reduction*

s p i r a l

A B S ~

c o n d u c t i n g r e f l e c t o r

l / 1 0

EBG Reflector l/10 ~ ~ l/100

x

y

l/100?

III MTM Antennas

IIIB Low-profile MTM Spirals

53

*Proposed Two-arm Spiral Antenna will be designed to meet two requirements.

- two feed points A and B *

- excited in balanced mode.

- Antenna arms: composed of numerous cells,

Cell * / two capacitors & one inductor.

Capacitors and inductor : : periodically added to the antenna arm.

G.P.( )8

CL CL

LL

.

1. Symmetrical Radiation Pattern

2. Extremely Low-profile Structure

F

(a) Perspective view.

x

y

o'A

B

SGPSsub

z

L M

LM- 1

54

Perspective view.

x

y

o'A

B

SGPSsub

z

L M

LM-1


2. Extremely Low-profile Structure

B = 1.6 mm

~ 0.013 wavelength at 2.5 GHz

.. An Antenna Height of 1.6 mm*

III MTM Antennas


55

b : phase constant along the arms

k0: phase constant in free space

fbalance : *balanced frequency : chosen to be 3 GHz

*Dispersion Diagram from 2 GHz to 5 GHz : Calculated Using Scattering Parameters [S]*

2 3 4 5-2

-1

0

1

2

b/k

0

Frequency [GHz]

fb ala nce

x

y

o'A

B

SGPSsub

z

L M

LM- 1

56

progressive regressive

fL : lower bound for a fast wave* fU : upper bound for a fast wave*

@ fL*, b/k0 = 1

@ fU*, b/k0 = 1

Dispersion Diagram

2 3 4 5 - 2

- 1

0

1

2

b / k

0

F r e q u e n c y [ G H z ]

f b a l a n c e f U f L

III MTM Antennas


57

RH-CP Radiation LH-CP

// Dual-band Counter-CP Radiation//

If the antenna size is appropriately chosen

will appear will appear

2 3 4 5 - 2

- 1

0

1

2

b / k

0

F r e q u e n c y [ G H z ]

f b a l a n c e f U f L

III MTM Antennas


58

.. An MTM Spiral having 6 Filaments.

~ The MTM spiral operates in the first mode.

Moderately wide-band characteristics:: Expected

Design

III MTM Antennas


59

L6

L6 = 6 cm = 0.5l2.5

* Frequency response of the gain

The maximum LH CP gain appears near the N-frequency.

The maximum RH CP gain appears near the H-frequency.

The gain has a moderately wideband characteristic

~ meets one of the requirement 2.

2.0 2.5 3.0 3.5 4.0 4.5 5.0-20

-15

-10

-5

0

5

10

15

20

Frequency[GHz]

GLfLH_ G

fL fbalan ce fU

fN fH

fR H_ G

GR

Ga

in(

= 0

,

= 0

)[d

Bi]

14.5%

14.0%

L6

Purposes


2. Moderately Wideband Characteristics

M = 6

III MTM Antennas


60

Radiation Pattern

2.6 GHz

0

-10

0o

30o

60o

270o

300o

330o

x

z

0

-10

0o

30o

60o

270o

300o

330o

x

z

- : symmetrical with respect to the z-axis

2.0 2.5 3.0 3.5 4.0 4.5 5.0-20

-15

-10

-5

0

5

10

15

20

Frequency[GHz]

GLfLH_ G

fL fbalan ce fU

fN fH

fR H_ G

GR

Ga

in(

= 0

,

= 0

)[d

Bi]

L6

x

y

3.7 GHz

Purposes


2. Moderately Wideband Characteristics

2.6 GHz

3.7 GHz

M = 6

E R

E L

61

2.0 2.5 3.0 3.5 4.0 4.5 5.01

2

3

4

5

6

7

8

9

Frequency [GHz]

fL

fLH- G

GL BW GR BW

fRH-G

fUfbalan ce

fN fH

VS

WR

80

3 dB-reduction Gain Band Width

Frequency response of the VSWR for M = 6 *

The VSWR : less than 2 within the gain bandwidth 2.0 2.5 3.0 3.5 4.0 4.5 5.0

-20

-15

-10

-5

0

5

10

15

20

Frequency[GHz]

GLfLH_ G

fL fbalan ce fU

fN fH

fR H_ G

GR

Ga

in(

= 0

,

= 0

)[d

Bi]

2.6 GHz 3.7 GHz

M = 6

L6

x

y

III MTM Antennas


62

Two-Arm MTM Spiral*

x

y

l/100

Dual-band Counter Circularly Polarized Radiation from a Single-arm Metamaterial-

based Spiral Antenna

in IEEE Trans AP, June, 2013 (accepted for publication)

Details of this work

A Monofilar MTM Spiral - does not require a balun circuit

- -

Effects of the pitch and ground plane

on the antenna characteristics :: *

x

ss u b(sG P)

ss u b(sG P)

LM

d

d

d

y

LM -1

B

F

Current Work

III MTM Antennas


63



Out line


Section IV Remarks











64

An incoming current should be reduced

to realize a wideband antenna.

Some natural antennas, specified by a positive-b current,

realize wideband characteristics,

having a low profile structure.

The antenna height can be reduced

using a metamaterial property,

which is featured by a negative-b current.

REMARKS

Antenna Height from l/4 to l/100

65

natural and metamaterial low-profile antennas with ... nakano.pdf · with emphasis on realization...

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