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Development of Electrically Small Planar Antennas with Matching Circuit

H. Kanaya, R. Nabeshima, R. K. Pokharel, and K. Yoshida

Department of Electronics, Graduate School of Information Science and Electronical Engineering,

Kyushu University, Japan

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　1: Introduction.

2: Design theory of electrically small antenna (ESA)with coplanar wave guide (CPW) matching circuit.

3: Fabrication and measurement of ESA.→Comparison of the patch, standard slot dipole with ESA.

　　4: Conclusion.

Outline

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Today’s small antennas

・Diversity Antenna ・Adaptive Array Antenna ・MIMO (Multiple-Input Multiple-Output)・RF-ID Tag・ ・ ・ ・

Example of Small Antennas

・ wireless LAN・ Bluetooth・ 3G & 4G・UWB・ Satellite telecommunications・ ・ ・ ・

Antennas Applications

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Today’s small antennas

・Diversity Antenna ・Adaptive Array Antenna ・MIMO (Multiple-Input Multiple-Output)・RF-ID Tag

Example of Small Antennas

RF devices < antenna size

Miniaturize antennas are necessary!

MIMO

・Antenna size・Two or more antennas

・ wireless LAN・ Bluetooth・ 3G & 4G・ Satellite telecommunications

Antennas Applications

RF-ID Tag

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Magnetic Current

maxmin

E-field Distribution

metal

λ/2 λ/2

slotmaxmin

Slot dipole antenna

Behdad, 2004, @UHF

Bhobe 2004 @5GHz, Wide band

Garcia,1999 @5GHz

Kanaya, 2002, @10GHzSlot antenna + 3-pole BPF

SignalGND

Coplanar wave guide (CPW)

Preferable for MMIC & RFIC ⇔No via holes

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Layout of the standard slot dipole antenna@2.4GHz

⎪⎪⎩

⎪⎪⎨

⎧

==

==

mmedgemmfeed

mmWmmL

00.100.5

0.180.38

Cross section copper0.018mm

FR4: εr=4.25 tanδ=0.015(@1.8GHz)

0.80mm

Y

XZ

θφ =0°

φ =90°

Zθ

YX φ

LW

feededge

24.0

mm

74.0mm

Peak Gain:3.192dBiRadiation Efficiency:96.07%

3-dimensional EM simulator (HFSS, Ansoft)

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2. Design theory of electrically small antenna (ESA)with CPW matching circuit.

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Electrically small antenna (ESA)

Small Radiation ResistanceNarrow bandwidth

Impedance Matching

Design of Bandwidth

Electrically Small AntennaAn antenna whose dimension is much smaller than quarter wavelength…

Sensitive to the conductor resistance

9

Layout of the electrically small antennaRadiation section

Cross section copper0.018mm

FR4 εr=4.25 tanδ=0.015 (@1.8GHz)

0.800mm

22.30mm(0.18λ0)

8.20

4mm

(0.0

67λ 0

)

Y

XZZa=Ra+jXa

Grad Gl

Z a=1/ Y a＝ 1/ (Ga+jBa )＝ 1/ ( Grad +Gl +jBa)

Grad：Radiation conductance

Gl： Conductance of the metal loss

Ba ：Antenna susceptance

Equivalent circuit of the ESA (@ Resonant frequency)

jBa

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Input impedance (Za) (a) and return loss (b) of the ESA without matching circuit.

-5

-4

-3

-2

-1

0

2 2.2 2.4 2.6 2.8 3

Ret

urn

Loss

[dB]

Frequency [GHz]

(b)

-2000

-1000

0

1000

2000

3000

4000

2 2.2 2.4 2.6 2.8 3

Ra

Xa

Ante

nna

Impe

danc

e (Z

a) [Ω

]

Frequency [GHz]

(a)

Return loss

Working frequency (2.4GHz)

Impedance Miss Match!!

Za=Ra+jXa

Za=42.5+j385 Ω

Ra=Radiation loss + Metal loss

(2.74GHz)λ/4 parallel resonance

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Electrically small antenna with matching circuit

Antenna with matching circuit

* For receiver

aavs R

VP

8

20=

Maximum available power

Antenna size is not included.

Zin = Za*⇒Pin　(Max)

Za：Antenna impedance

V0：Receiving voltage

202

]Re[21 V

ZZZP

ina

inin

+=

ae GAπ

λ4

2

=

Effective aperture Za= Ra+jXa

MatchingCircuit

V0

ZaPin

Zin

ZL

ESA RF front- endA

A’

Loss less

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Circuit model of the n=1 bandpass filter (a) and equivalent circuit model at center frequency (b)

0

101

0

011

21

0112

10

1001

2,

ωωωω

ωω

ωω

=∂∂

=⎟⎟⎠

⎞⎜⎜⎝

⎛−=

=

=

BbbB

ggYb

wJ

ggbY

wJ

J1,2jB1J0,1 Y0Y0

(a)

(b)

jB1

2

2

eL Q

bG =′1

1

es Q

bG =′

⎪⎩

⎪⎨

⎧ −

parameter slope eSusceptanc:resonator parallel in the eSusceptanc:inverter)(invertereSusceptanc:

1

1

bB

JJ ij

⎩⎨⎧

parameterFilter:bandwidthRelative:

igw

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Circuit model of the n=1 impedance matching circuit (a) and equivalent circuit model at center frequency (b)

Antenna Amp.

Za Z01=1/Y01 ZL

Cm

LLLL jBGY

Z+

==11

θ01 −θ02

θ0

aaaa jBGY

Z+

==11

jB’G’ Yin’

Y’Yin’(a)

(b)

A

A’

B

B’

Zin

⇒ Conventional design theory of n=1 bandpass filter

J-inverter

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Theory of the matching circuit（n=1）

Y’: The admittance for looking the antenna from A-A’

Y’in : The admittance for looking the amplifier from A-A’

0101

010101 tan

tan''θθ

a

a

jYYjYYYjBGY'

++

=+=

)2(0' 010

πθωω

≤==

B

0

),('2

' 01010

ωωωθω

=∂∂

=ZB

b

)tan(/11

)tan(/11

'''0201

0201

θω

θω

−+

+

−++

=+=

mL

mLininin

CjZjY

jYCjZjBGY

①

② ⎟⎠⎞

⎜⎝⎛==

wggQ

Gb

e10

1''

θ01,Z01 are derived from ①,② θ02,Cm are derived from ③,④

)2(0' 020

πθωω

≤==inB③

④ ⎟⎠⎞

⎜⎝⎛==

wggQ

Gb

ein

212'

'

A

Antenna Amp.

ZaZ01=1/Y01 ZL

Cm

LL Y

Z 1=

θ01 −θ02

Y’ Yin’

A’

B

B’

Zin

aa Y

Z 1=

J-inverter

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Layout of the electrically small antenna with CPW feed line

22.30mm

8.20

4mm

Y

XZ

Y’A A’ CPW feed line

(Z01=1/Y01, θ01)

A

Antenna Amp.

Za Y01 ZL

Cm

LL Y

Z 1=

θ01 −θ02

Y’ Yin’

A’

B

B’

Zin

aa Y

Z 1=

J-inverter

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Input admittance (Y’) of the ESA with CPW feed line

-4

-3

-2

-1

0

1

2

3

4

2 2.2 2.4 2.6 2.8 3

G'B'

Inpu

t adm

ittan

ce (Y

') [m

S]

Frequency (GHz)

Expected frequency (2.4GHz)

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Layout of the electrically small antenna with CPW feed lineand negative electrical length (-θ02)

22.30mm

8.20

4mm

Y

XZ

A A’

A

Antenna Amp.

Za Y01 ZL

Cm

LL Y

Z 1=

θ01 −θ02

Y’ Yin’

A’

B

B’

Zin

aa Y

Z 1=

−θ02

J-inverter

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Final layout of the ESA with CPW matching circuit8.

204m

m(0

.067

λ 0)

22.30mm (0.18λ0)L1

1mm

L2

W

Inverter

⎪⎪⎪⎪

⎩

⎪⎪⎪⎪

⎨

⎧

==

=−===

mmToothWidthmmhToothLengt

mmSpaceJmmWmmL

mmL

148.0200.0

300.000.160.40.10

2

1

J-Space

Tooth LengthTooth Width

Zin

B B’

A Zin

Za Y01 ZL

Cm

θ01 −θ02

Y’ Yin’

A’

B

B’

Cm

J-inverter

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Return loss (a) and Smith chart (b) of the ESA with matching circuit

-35

-30

-25

-20

-15

-10

-5

0

2 2.2 2.4 2.6 2.8 3

Ret

urn

Loss

[dB

]

Frequency [GHz]

(a)(b)

RL=-32.58[dB]

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Input impedance of the ESA with matching circuit①

Zin=49.03+j2.149[Ω]@2.41GHz

-300

-200

-100

0

100

200

300

2 2.2 2.4 2.6 2.8 3

Re[Zin]

Im [Zin]

Inpu

t Im

peda

nce

(Zin) [

Ω]

Freqency [GHz]

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Simulated radiation pattern of the ESA

Z

X

Y

θ

φ

θφ =0°

φ =90°

Z

Y

X

↑Dipole antenna

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Photographs of the antenna fabrication

PCB

Printed board making equipment (MITS Co.)

High-frequency Milling Cutter

φ =100µm drill is inside

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Photograph of the ESA

MMCX connector (50Ω)

0.30mm

Inverter⇒Interdigital gap

RF-in

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Photographs of the RF measuring system

Vector Network Analyzer:HP8722C

PC: AgilentADS

VNA

Antenna

MMCX-SMAConnector

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Experimental results and simulated results of consideringpermittivity error

ε r :4.25→4.05

Exp.

Sim.

-35

-30

-25

-20

-15

-10

-5

0

2 2.2 2.4 2.6 2.8 3

Ret

urn

Loss

[dB

]

Frequency [GHz]

2.4472.451

f0 [GHz]

42MHz （2.427-2.469[GHz]）Measurement53MHz （2.426-2.479[GHz]）Simulation

Band Width(@-10dB)

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Comparison of the standard dipole antenna with the ESA with matching circuit

-2.744dBi3.192dBiGain

63.12%96.07%Radiation Efficiency

35[mm]145[mm]Communication distance

22.3*8.204[mm2]74.0*24.0 [mm2]Size

ESAStandard dipole

:EM sim.

6dB

4times

90% saved !!

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Conclusions

　Using the theory of the bandpass filter

　Using the commercial 3-dimentional EM simulator

　　　⇒The antenna size can be reduced to about 90 % and 　　　　　bandwidth design becomes possible.

　Fabricated and tested the ESA with CPW matching circuit

　　　⇒ RF properties

　　　⇒ Communication distance

We succeeded in realizing the circuit which matches the small radiation resistance of ESA to the amplifier.

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Target in the future: RF front-end on ESA

8.5mm×7mm

All-in-one design of RF front end on ESA in 10mm2

substrate @2.45GHz (IMS band).

MCT+LNA+MX+VCO(1.2mm×3.5mm)Tomorrow's workshopR.K.Pokharel, Kyushu univ.

LNABPF+MatchingCircuit

BPF+MatchingCircuit

Down conversion Mixer

VCO

MatchingCircuit

Base band

Antenna

LNABPF+MatchingCircuit

BPF+MatchingCircuit

Down conversion Mixer

VCO

MatchingCircuit

Base band

Antenna

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Thank you for your attention !!