1

Transparent Antennas: From 2D to 3D

Transparent Antennas: From 2D to 3D

K. W. LeungState Key Laboratory of Millimeter Waves &

Department of Electronic Engineering,City University of Hong Kong

2

I. 2D transparent antenna

Meshed conductor Transparent conductor

II. 3D transparent antenna

Optical application Decoration Light cover

Outline

3

I. 2D Transparent AntennaI. 2D Transparent Antenna

4

Based on the theory of microstrip antenna.

Meshed conductors or transparentconductors on acrylic or glass substrates.

Integrated with planar clear substratessuch as window glass or with solar cells.

2D transparent antenna

5

Transparent Antenna UsingMeshed Conductor

Transparent Antenna UsingMeshed Conductor

6

Working principle: optical signal passthrough the opening, microwave signaltransmitted or received by conductor.

Not fully transparent.

Meshed conductor

7

Proposed by Wu & Ito in 1992.Microstrip antenna & ground plane made with parallel wiresWires: silver-plated copper of cross section 0.2 0.1 mm2

Glass substrate.

Early transparent antenna

M. S. Wu and K. Ito, “Basic study on see-through microstrip antennas constructed on a window glass,” in Proc.IEEE AP-S Int. Symp., pp. 499–502, 1992. 8

8

Measured return loss vs. frequency

Measured bandwidth (VSWR < 2): 1.5%.

9

Measured radiation patterns

Broadside radiation patterns obtained for both planes.Front-to-back ratio ~ 9 dB.Cross polarization level < -13 dB in the boresight direction ( = 0).

10

Measured gain

Measured gain at 925 MHz: ~ 2.5 dBd (relative gain tostandard dipole antenna: 2.15 dBi).

11

Transparent Antenna Using Transparent Conductor

Transparent Antenna Using Transparent Conductor

12

Proposed by Simons & Lee in 1997.(a) Microstrip Line Feed: a=53mm, b=37mm, d=8 mm, w=2 mm (6 GHz).(b) Probe Feed: a = 9 mm, b = 7 mm (19 GHz).

(a) (b)

The first transparent antennas using conductive film

R. N. Simons and R. Q. Lee, “Feasibility Study of Optically Transparent Microstrip PatchAntenna”,NASA Technical Memorandum, 1997. 21

13

Transparent conductive materials (TCO)

TCO found since the 1950s

Quickly developed over the past decades.

Products include paper-thin LCD, plasma, touch screen monitors on ATMS, etc.

Common TCO’s:Indium tin oxide (ITO), silver coated polyester film (AgHT) and fluorine-doped tin oxide (FTO).

14

ITO

AgHT

FTO

Transparent conductive materials (TCO)

15

The surface resistance is given by:

Rs=1/(Ne qμe t)

where μe is the electron mobility, Ne is the free electron density,q is electron charge, andt is the film thickness.

Resistance of ITO film

T.Yasin, R. Baktur, and C. Furse, "A study on the efficiency of transparent patch antennas designed fromconductive oxide films," IEEE International Symposium on Antennas and Propagation, pp3085 - 3087, 2011.24

16

Effect of electron mobility on radiation efficiency

Given an electron mobility, higher transparency leads to lower efficiency.

17

Transparent monopole antenna

The trapezoidal radiator is made of ITO film.The ground is made of copper.

Ning Guan, Hirotaka Furuya, David Delaune, and Koichi Ito, “Antennas Made of Transparent ConductiveFilms, PIERS.Vol. 4 No. 1 2008 pp: 116-120. 28

18

Measured radiation patterns

The resistance does not affect the radiation pattern significantly.

19

Method of improving the efficiency

H. J. Song, T. Y. Hsu, D. F. Sievenpiper, H. P. Hsu, J. Schaffner and E. Yasan, “A Method for Improving theEfficiency of Transparent Film Antennas”, IEEE Antennas and Wireless Propagation Letters, Vol.7, pp.753-756,2008. 33

Symmetrical half structure of coplanar waveguide fed patch antenna

20

Surface current distribution at 2.2 GHz

To improve efficiency,

apply a highly conductivecoating or metallization inthe form of a very narrowstrip.

21

Simulated efficiency for different strip widths

Copper patch has the highest efficiency as expectedAgHT-4 film (4.5 /sq, = 2.2 105 S/m) without adding silver strip

38% efficiencyAgHT-4 film with silver strip (1-mm strip width) along the edge:

68% efficiency equivalent to a conductor patch with 0.4 /square

22

II. 3D Transparent AntennaII. 3D Transparent Antenna

23

Based on theory of dielectric resonator antenna (DRA).

3D transparent antenna

• The DRA is an antenna that makes use of a radiating mode of a dielectric resonator (DR).

• It is a 3-dimensional device of any shape,e.g., hemispherical, cylindrical, rectangular,triangular, etc.

• Resonance frequency determined by the its dimensions and dielectric constant r.

24

Some DRs :

25

Glass is used as the dielectric material

Well-known fact:Refractive index of glass: n ~ 1.5 r ~ 2.25

This r is too low for designs of DRAs

But something has been overlooked …..

3D transparent antenna

26

n ~ 1.5 (r ~ 2.25) is for optical frequency only r can be very different at microwave frequency

Dielectric constant of the glass DRA

1 2 3 4 5 60

2

4

6

8

Frequency (GHz)

Dielectric constant

K9 glassTeflonAir

Measured dielectric constants of air, Teflon, and K9 glassby using Agilent 85070D Dielectric Probe Kit.

27

K-9 Glass

28

Transparent Dielectric Resonator Antennas for Optical Applications

Transparent Dielectric Resonator Antennas for Optical Applications

29

Hemispherical transparent DRA

Solar Cell

r, n

TransparentHemispherical DRA

Ground Plane

R

d

x

z

g

ConformalExcitation Strip

Coaxial Probe

l s

Substrate (rs)

Transparent Hemispherical DRA

x

y

ws

ConformalExcitation Strip

GroundedSubstrate

R

Rc

Solar Cell

Conformal strip for exciting the transparent DRA made of Pyrex.DRA serves as light-focusing lens for a solar cell panel.Underlaid solar cell panel to save the footprint.DRA provides protection for the solar cell panel.

E. H. Lim and K. W. Leung, “Transparent dielectric resonator antennas for optical applications,” IEEETrans. Antennas Propagat., vol. 58, No. 4, pp. 1054-1059, April 2010. 39

30

Solar cell r = 1.5, tan = 10 from the paper shown below

Prototype

Design parametersR = 28 mm, r = 7, g = 2 mm, d = 1.57 mm, ws = 12 mm, and ls =19 mm.

30J. Dheepa, R. Sathyamoorthy, A. Subbarayan, S. Velumani, P. J. Sebastian, and R. Perez, “Dielectric properties ofvacuum deposited Bi2Te3 thin films,” Solar Energy Mater. Solar Cells, vol. 88, no. 2, pp. 187–198, Jul. 2005.39

31

Prototype

3139

32

1.6 1.8 2 2.2 2.4-40

-30

-20

-10

0

Frequency (GHz)

HFSS SimulationExperiment

1.6 1.8 2 2.2-50

0

50

100

Frequency (GHz)

Inpu

t Im

peda

nce

|S11| (dB)

Simulated and measured S11 and input impedances

Resonance frequency: Measured 1.94 GHz Simulated 1.89 GHz (2.65% error)

Impedance bandwidth: measured 16.5%, simulated 22.8%

33

1.6 1.8 2 2.2 2.4-6

-3

0

3

6

9

Frequency (GHz)

Gain (dBi)

Measured antenna gain

The gain is ~5.3dBi around the resonance.

34

-40 -30 -20 -10 0 -40 -30 -20 -10 0

30

150

60

120

9090

120

60

150

30

180

o

o o

o

o o

o o

o oo

dB

30

150

60

120

90 90

120

60

150

30

180

o o

o o

o o

o o

o oo

dB

co-polcross-pol cross-pol

E-plane H-plane(a) (b)

Simulation 1.89GHzExperiment 1.94GHz

(x < 0, = 180 )o (y < 0, = 270 )o (y > 0, = 90 )o(x > 0, = 0 )o

0o 0o

Simulated and measured radiation patterns

Measured (1.87 GHz), simulated (1.92 GHz).In the boresight direction, co-pol fields > X-pol fields bymore than 22dB.

35

Prism

A rgonB lue Laser

Parallel L ight

Solar C ell

D R A

400m m 420m m

R otator

Experimental setup for the optical part

Parallel light beams generated by a laser source.(wavelength 488 nm, light power 130 mW)DRA placed on a rotator.Solar cell output measured at different illumination angles ().

36

Voltage (V)

0 10 20 30 40 50 60 70 80 900

0.5

1

1.5

2

2.5

Illumination Angle

With hemispherical DRAWithout hemispherical DRA

Current (mA)

0 10 20 30 40 50 60 70 80 900

0.5

1

1.5

2

2.5

Illumination Angle

With hemispherical DRAWithout hemispherical DRA

Output voltages and currents of solar panel with and without the hemispherical DRA: Rc = 15mm.

Larger outputs < 30o because of DRA focusing effect.At = 0o, output voltage and current increased by 13.5%

and 27.2%, respectively.

37

Non-focusing transparent DRA

Solar Cell

r, n

TransparentRectangular DRA

Ground Plane

W

d

x

z

g

Excitation Strip

Coaxial Probe

l s

Substrate (rs)H

TransparentRectangular DRA

y

x

ws

Excitation Strip

W

W

Rc

GroundedSubstrate

Solar Cell

Transparent rectangular DRA is used.

38

1.6 1.8 2 2.2 2.4-40

-30

-20

-10

0

Frequency (GHz)

HFSS SimulationExperiment

1.6 1.8 2 2.2-40

0

40

80

Frequency (GHz)In

put I

mpe

danc

e

|S11| (dB)

Simulated and measured S11 and input impedances

Resonant frequency: Measured 1.91GHzSimulated 1.86GHz (error 2.7%)

Impedance bandwidth: Measured 17.6 %, Simulated 15.8%.

39

1.6 1.8 2 2.2 2.4

-6

-3

0

3

6

Frequency (GHz)

Gain (dBi)

Measured antenna gain

Measured antenna gain: ~4 dBi at resonance.

40

-40 -30 -20 -10 0 -40 -30 -20 -10 0

30

150

60

120

9090

120

60

150

30

180

o

o o

o

o o

o o

o oo

dB

30

150

60

120

90 90

120

60

150

30

180

o o

o o

o o

o o

o oo

dB

co-polcross-pol cross-pol

E-plane H-plane(a) (b)

Simulation 1.86GHzExperiment 1.91GHz

(x < 0, = 180 )o (y < 0, = 270 )o (y > 0, = 90 )o(x > 0, = 0 )o

0o 0o

Simulated and measured radiation patterns

Measured (1.91 GHz), simulated (1.86 GHz).In the boresight direction, co-pol fields > X-pol fields by more than 25 dB.

41

Voltage (V) Current (mA)

0 10 20 30 40 50 60 70 80 900

0.5

1

1.5

2

2.5

0

0.4

0.8

1.2

1.6

2

Illumination Angle

With rectangular DRWithout rectangular DR

Output voltages and currents of solar panel withand without the rectangular DRA: Rc = 15mm.

The rectangular DRA does not increase the solar cell outputs No focusing effect.

42

Transparent Dielectric Resonator Antennas Used as Decorations

Transparent Dielectric Resonator Antennas Used as Decorations

43

DRA can be of any shape. Can it be made like a swan?

Yes!

It leads to probably the most beautiful antenna in the world …….

44 K. W. Leung, E. H. Lim and X. S. Fang, "Dielectric resonator antennas: From the basic to the aesthetic,"Proceedings of the IEEE, vol. 100, no. 7, pp2181-2193, Jul. 2012.

Broadside Transparent Swan-DRA (K9 glass)

Bought from commercial market, not tailor-made

44

45

Advantages of aesthetic transparent DRA

Home or office decorations

Save space

Turn antennas into artworks

Excellent invisible antennas

133

27

103

115

13

57

13 34

33

z

x

z

y

3

133

43

Antenna Configuration

Side view Front view

Dimension in mm

Substrate: εrs= 2.33, thickness 1.57 mm, size 1414 cm2

46

Antenna Configuration

2

32 130

51

140

z

-y10

y

x

140

Back view Top view

Dimension in mm

Coupling slot: at center of swan length (130 mm) Slot size: length 32 mm, width 2 mm 47

48

Measured reflection coefficient

Resonance frequency: 1.83 GHzImpedance bandwidth: 31.6 % (1.57 - 2.16 GHz)

1.6 1.8 2 2.2 2.4

-20

-10

0

Frequency (GHz)

Reflection coefficient |S | (dB)11

Verification of swan resonance, not slot resonance

(1) Reflection coefficient

49

50

1.6 1.8 2 2.2 2.4 2.60

2

4

6

8

Frequency (GHz)

Gain (dBi)

• Maximum gain: 7.4 dBi (1.84 GHz)• Much higher than that of the slot antenna

(2) Antenna gain

51

Measured radiation patterns at 1.8 GHz

-40 -30 -20 -10 0

30

150

60

120

90

120

60

150

30

180

0oo

o o

o

o o

o o

o oo

dB

90 90

150180

o

o

o

oo

dB-40 -30 -20 -10 0

30

150

60

90

120

60

150

30

180

0 oo o

o o

o o

o o

o oo

dB

H-plane (x-z plane)E-plane (y-z plane)-y

120

+y -x +x

Cross-pol Cross-pol

Co-pol

(a) (b)

Broadside radiation patterns observed.Co-pol > X-pol by more than 20 dB in the boresight

direction for both E and H planes

52

Application:Wireless video system

Transmitter

Receiver

53

Transmitter

DVD Player

Swan-DRA

Modulator

SlotMicrostripline

Transmitter

54

Receiver

Antenna

Demodulator

LCD monitor 55

56

Video

57

Slot-coupled Apple-DRA

K. W. Leung, E. H. Lim and X. S. Fang, "Dielectric resonator antennas: From the basic to the aesthetic,"Proceedings of the IEEE, in press. 67

58

z

x

50

50 2 25

75 75

20

49

y

x

11

75

Made of K-9 glass. Slot-coupled at the center. Design parameters:

Coupling slot: length L = 25 mm, width W = 2 mm.Substrate: εrs= 2.33, thickness d = 1.57 mm, size 55cm2.Microstrip feedline: width Wf = 4.7 mm, stub length Ls = 9 mm.

Antenna Configuration

59

-40 -30 -20 -10 0

30

150

60

120

9090

120

60

150

30

180

0oo

o o

o

o o

o o

o oo

dB

90 90

150180

o

o

o

oo

dB-40 -30 -20 -10 0

30

150

60

90

120

60

150

30

180

0 oo o

o o

o o

o o

o oo

dB

H-plane (x-z plane)E-plane (y-z plane)-y

120

+y -x +x

Cross-pol Cross-pol

Co-pol

(a) (b)

Broadside radiation patterns are observed.For both E plane and H plane, co-pol fields > X-pol fields by more than 20 dB in the boresight direction.

Measured radiation patterns of the Apple-DRA at 1.8 GHz

60

Transparent Omnidirectional Building-shaped DRA

61

Probe-fed at the center.Design parameters:

DRA: Height 93 mm, square bottom of 21×21 mm2.Circular ground plane: Diameter of 19 cm.Coaxial probe: Length 19 mm, radius 0.635 mm.

z

x

23 12 14 25 14 5

14 9

14 93

21

y

1.27

19190

Antenna Configuration

62

Measured reflection coefficient

• Resonance frequency: 2.89 GHz• Impedance bandwidth: 36.5% (2.48 -3.59 GHz)

2 2.5 3 3.5 4-30

-20

-10

0Reflection coefficient |S | (dB)11

Frequency (GHz)

)4/( rlcf

)4/(3 rlcf

where f : resonance frequency of probe, c : speed of light in air, εr : dielectric constant of K9 glass.

Fundamental mode:

First higher-order mode

Verification of DRA resonance, not probe resonance

Estimation of probe resonance frequency (l = 19 mm)

= 1.5 GHz (εr = 6.85)

= 4.5 GHz (εr = 6.85)

63

64

Omnidirectional radiation pattern

Measured radiation patterns（2.48 GHz）

-40 -30 -20 -10 0

30

150

60

120

9090

120

60

150

30

180

o

o o

o

o o

o o

o oo

dB

90 90

150180

o

o

o

oo

dB-40 -30 -20 -10 0

30

150

60

90

120

60

150

30

180

o o

o o

o o

o o

o oo

dB

120

-x +x

0o= 0o=

x-z plane 60o=

Col-pol

Cross-polCross-pol

65

Measured radiation patterns（2.89 GHz）

-40 -30 -20 -10 0

30

150

60

120

9090

120

60

150

30

180

o

o o

o

o o

o o

o oo

dB

90 90

150180

o

o

o

oo

dB-40 -30 -20 -10 0

30

150

60

90

120

60

150

30

180

o o

o o

o o

o o

o oo

dB

120

-x +x

0o= 0o=

x-z plane 60o=

Col-pol

Cross-pol

Cross-pol

Stable radiation pattern

66

Measured radiation patterns（3.59 GHz）

-40 -30 -20 -10 0

30

150

60

120

9090

120

60

150

30

180

o

o o

o

o o

o o

o oo

dB

90 90

150180

o

o

o

oo

dB-40 -30 -20 -10 0

30

150

60

90

120

60

150

30

180

o o

o o

o o

o o

o oo

dB

120

-x +x

0o= 0o=

x-z plane 60o=

Col-pol

Cross-pol

Cross-pol

Influenced by a higher-order DRA mode

67

Transparent Dielectric Resonator Antennas Used as a Light Cover

Transparent Dielectric Resonator Antennas Used as a Light Cover

68

Hollow hemispherical DRA used as a light cover

69

Advantages of light-cover antenna

Indoor antennas widely found in modern buildings

Light-cover antennas can be mounted on ceilings

Lighting and antenna systems combined - save space

Both systems installed in one go - save cost & work

Excellent invisible antennas - avoid uneasy feeling ofradiation

70

r

Hollow region

Ground plane

Transparent hollow hemispherical DRA

Feedline Coupling slot

x

z

d

a2 a1

To power supplyLED

rs

Antenna configuration

Made of K-9 glass. Slot-coupled at the center. Design parameters:

Hollow hemispherical DRA: a1 = 21.8 mm, a2 = 9.6 mm.Coupling slot: length L = 26 mm, width W = 1.8 mm.Substrate: εrs= 2.33, d = 1.57 mm, a size of 1515cm2.Microstrip feedline: Wf = 4.8 mm, Ls = 10.8 mm.

Coupling slot

Feedline

Transparent hollow hemispherical DRA

Ly

x

Wf

W

Ls

LED

71

Measured and simulated S11

Measured bandwidth (without LED): Lower band (TE111 mode): 20.96% (2.22-2.74 GHz)Upper band (TE112 mode): 10.4% (5.49-6.09 GHz)Measured bandwidth (with LED): Lower band: 20.96% (2.22-2.74 GHz), Upper band: 10.2% (5.49-6.08GHz).

Reflection coefficient |S | (dB)11

Frequency (GHz)2 3 4 5 6

-30

-20

-10

0

TE111

TE311

TE112

Simulation (without LED)Measurement (without LED)Measurement (with LED)

72

Field distribution

TE111 mode: 2.45 GHz TE112 mode: 5.86 GHz

73

Measured (2.48 GHz), simulated (2.48 GHz).Broadside radiation patterns are observed for both planes.Co-polarized fields > cross-polarized fields by more than

18 dB in the boresight direction.

Lower-band radiation patterns

-40 -30 -20 -10 0

30

150

60

120

9090

120

60

150

30

180

o

o o

o

o o

o o

o oo

dB

90 90

150180

o

o

o

oo

dB-40 -30 -20 -10 0

30

150

60

90

120

60

150

30

180

o o

o o

o o

o o

o oo

dB

120

H-plane (y-z plane)E-plane (x-z plane)-x +x -y +y

Simulation (without LED)

Measurement (without LED)

Measurement (with LED)

0o= 0o=Co-pol

X-pol X-pol

74

Upper-band radiation patterns

Measured (5.8 GHz), simulated (5.8 GHz).Broadside radiation patterns are observed for both planes.Co-polarized fields > cross-polarized fields by more than

20 dB in the boresight direction.

-40 -30 -20 -10 0

30

150

60

120

9090

120

60

150

30

180

o

o o

o

o o

o o

o oo

dB

90 90

150180

o

o

o

oo

dB-40 -30 -20 -10 0

30

150

60

90

120

60

150

30

180

o o

o o

o o

o o

o oo

dB

120

E-plane (x-z plane)

-x +x

Simulation (without LED)

Measurement (without LED)

Measurement (with LED)

0o=0o= Co-pol

X-pol X-pol

H-plane (y-z plane)

-y +y

75

Maximum lower-band gainWithout LED: 5.26dBi (2.44GHz), with LED: 5.43dBi (2.48GHz)Maximum upper-band gainWithout LED: 7.08dBi (5.9GHz), with LED: 6.76dBi (5.88GHz)LED only has negligible effect on the DRA performance.

Measured and simulated antenna gains

2 2.5 3 3.5 4 4.5 5 5.5 6-4

-2

0

2

4

6

8

10

12

Frequency (GHz)

Antenna gain (dBi)

Simulation (without LED)Measurement (without LED)Measurement (with LED)

76

Side view Top view

Omnidirectional rectangular glass DRA

77

Perspective view Bottom face

Omnidirectional rectangular glass DRA

78

79

Measured and simulated S11

Measured bandwidth (without LED): 28.8% (1.992.66 GHz)

1.8 2 2.2 2.4 2.6 2.8 3-30

-20

-10

0

Frequency (GHz)

|S11| (dB)

HFSS SimulationMeasurement (without LEDs)Measurement (with LEDs)

Probe mode DRA TM mode

80

Measured (2.40 GHz), simulated (2.40 GHz).Omnidirectional radiation patterns are observed.Co-polarized field > cross-polarized field by 20 dB or more.

Measured and simulated radiation patterns

( = 180 ) ( = 60 )oo ( = 0 )o

Co-pol

-40 -30 -20 -10 0

30

150

60

120

9090

120

60

150

30

180

o

o o

o

o o

o o

o oo

dB

0o

X-pol

-40 -30 -20 -10 0

30

210

60

240

90270

120

300

150

330

180

o

o o

o

o o

o o

o oo

dB

0o

X-pol

81

Measured antenna gain : 1.8 dBi (@2.4 GHz)

Measured and simulated antenna gains

1.8 2 2.2 2.4 2.6 2.8 3-4

-3

-2

-1

0

1

2

3

4

Frequency (GHz)

Gain (dBi)

HFSS SimulationMeasurement (without LEDs)Measurement (with LEDs)

82

Circularly polarized (CP) glass antenna design

In general, why CP antennas are needed?

Faraday effect

Fading effect

Alignment between transmit and receiveantennas can be relaxed.

83

84

Problem:

Copper strip not transparent

Solution:

Use transparent AgHT-coated glass strip

Drawback:

Lossy => reduction in efficiency

85

86

2.2 2.3 2.4 2.5 2.6 2.70

0.2

0.4

0.6

0.8

1

Frequency (GHz)

Efficiency

Copper patchITO glass without LEDsITO glass with LEDs

87

88

Integration of glass DRA with table lamp

89

Integration of glass DRA with table lamp

Save space

Excellent invisible antenna

Table-lamp antenna applied to a wirelessvideo system.

It is used in the transmitter.

It can also be used in the receiver.

90Modulator

Feeding probe

LEDs

Ground plane

Light-cover &Glass antenna

91

Video

9292

• 2D transparent antenna based on patch-antenna theory hasbeen briefly explained.

• Meshed or transparent conductors are normally used for 2Dtransparent antennas.

• 3D transparent antenna based on DRA theory has beenpresented.

• The transparent DRA can be used as a focusing lens,decoration, or light cover.

Conclusion

93

Thank you !Thank you !

94

Q & AQ & A