angefertigt von cand.-ing. umut bulus bei prof. dr.-ing. k ...umut bulus, 20.03.2008 page 4...

Mobile Phone Antenna Modelling

Umut Bulus

Supervised byProf. Dr.-Ing. K. Solbach

20.03.2008

Master Thesis

Umut Bulus, 20.03.2008

Contents

• Introduction

• Theoretical Background

• Antenna Measurements on Different PCB Variations

• Investigation of the Chassis

• Investigation of Coupling between the Antenna Element and Chassis

• Modelling and Optimizing the Structure (Antenna Chassis Combination)

• Conclusion


Introduction

• Integrated Antenna element couples strongly with the PCB

• PCB acts as a second radiator

• Increase efficiency

• Bandwidth of the antenna

• Integrated Antenna element couples strongly with the PCB

• PCB acts as a second radiator

• More Efficiency

• More Antenna Bandwidth


Introduction

The thesis task

• Design and test of Monopole and PIFA antennas on a large ground plane

• Reflection coefficient measurement of antennas mounted on PCB at

• Different Positions

• Orientations

• PCB Length Variations

• Test of the PCB as a dipole antenna via a balun and coaxial cable

• Investigation of the coupling between the antenna element and PCB by 2

port measurements at different antenna element

• Positions

• Orientations

• Developing an equivalent circuit representation of the antenna element, the

coupled PCB and the coupling mechanism


Theoretical Background

Potential Bandwidth:

• The bandwidth for the best matching case

• The impedance of the center frequency is selected as

the characteristic impedance.

• The reflection coefficient is approximately zero for the

center frequency

• So, the potential bandwidth could be found between

the -10 dB frequency points.


Antenna Measurements on Different PCB Variations

Antenna Designs on Large Ground Plane (42.5 cm 50 cm)

• No Simulation Tool

• Monopole Antenna

• Center Frequency: 1.047 GHz• Bandwidth: 12.3 %• Gain Maximum at 1 GHz: 2.261 Db

• PIFA Antenna


• C-Patch Antenna


Χ



Orientation

• ∆F = -

Orientation Number 1



-0,1

-0,05

0

0,05

0,1

0,15

1 2 3

Orientation Number

∆ F

/ [G

Hz]

C Patch PIFA

05

101520253035

1 2 3

Orientation Number

PBW

[%]

C Patch PIFA

orientedf groundelf arg



Antenna Position Change on the PCB

• Antennas at Orientation Number 3

• The dots indicate the Feed Points

• ∆F = -

05

101520253035

1 2 3

Position Number

PBW

[%]

C Patch PIFA Monopole

-0,1

-0,05

0

0,05

0,1

0,15

1 2 3

Position Number

∆ F

/ [G

Hz]

C Patch PIFA Monopole

groundelf argpositionf



Variation of PCB Length

• Antennas at Orientation Number 3

• The dots indicate the Feed Points

• PCB is cut in every 30 mm between 300 mm to 90 mm

• ∆F = -lengthPCBf groundelf arg

05

101520253035

90 120 150 180 210 240 270 300

PCB Length / [mm]

BW

[%]

At the edge In the middle

-0,1

-0,05

0

0,05

0,1

0,15

90 120 150 180 210 240 270 300

PCB Length / [mm]

∆ F

/ [G

Hz]


Monopole Antenna



PIFA Antenna

C-Patch Antenna

05

101520253035

90 120 150 180 210 240 270 300

PCB Length / [mm]

BW

[%]


-0,1

-0,05

0

0,05

0,1

0,15

90 120 150 180 210 240 270 300

PCB Length / [mm]

∆ F

/ [G

Hz]


05

101520253035

90 120 150 180 210 240 270 300

PCB Length / [mm]

BW

[%]


-0,1

-0,05

0

0,05

0,1

0,15

90 120 150 180 210 240 270 300

PCB Length / [mm]

∆ F

/ [G

Hz]


Most Bandwidth

• Orientation Number 3

• Antenna located at the top edge of the PCB

• Around 130 mm PCB Length


Investigation of the Chassis

• The chassis is cut into two arms and measured as a dipole antenna

• 2 baluns and 4 different methods

• Providing Symmetric excitation using an unbalanced coaxial feeding cable


Investigation of the ChassisFirst, measuring the chassis as

a monopole

• Monopole is conversion of Dipole Antenna

• The possibility to use the unbalanced coaxial feed

• 15 degree dipole antenna measurement in the frequency range of 80-2000 MHz

• Resonance Impedance 19 ohm, so for dipole, it should be around 38 ohm

• Resonance frequency 646 MHz

S11 of the MonopoleAntenna



• Second, Dipole Simulations of the Chassis at different angles in the frequency range of 500-2000 MHz

S11 of 45 degreechassis


S11 of 30 degreewith straight part


S11 of straightchassis

Center Frequency

PBW

45 degree 620 MHz 20 %


30 degree with straight

785 MHz 55 %


Straight 860 MHz 82 %



S11 of 10 ohm

S11 of 56 ohm

• Finally, 1:1 RF Transformer Method (350-1500 MHz)

• The tests of open, short terminals and 10, 56, 220 ohm resistors are done.

• Finally, the reference plane is selected as primary port of the transformer and the balun is excluded by the formula;

• is the reflection coefficient of the dipole

• Improved by zeroizing and and by using a ferrite core to suppress the current flow on the outer part of the coaxial cable

inΓ

11S 22S

L

Lin S

SSSΓ−Γ

+=Γ22

122111 1

220220

100−MeasuredZError percentage of

the method [%] =


Investigation of the Chassis• The reason of the spreads in the

10, 56, 220 ohm tests is analyzed as non-linear phase variation with frequency of the RF Transformer which is not correctly compensated by the electrical delay.

• 15 degree of non-linear insertion phase

• In the simulation of 30 degree dipole;

• Impedance value changes between 34.5 to 121.7 ohm

• Average impedance is 84 ohm

• Very high error percentage at 10 ohm

• More accurate than 10 ohm at 220• Acceptable error percentage closer

to 56 ohm

• 350-1200 MHz interval is found as acceptable

S11 of 220 ohm



• Reflection Coefficient of 30 degree dipole antenna measured in the frequency range of 350-1200 MHz

• The center frequency is 747 MHz and the resonance impedance is 27 ohm

• PBW is 42 %

• Comparable with the simulations




• The gain of the 30 degree dipole antenna measured at 1 GHz

• E-Plane

• 5 Db maximum gain• 70 degree HPBW• Dynamic range 32 Db

• H-Plane

• 6.44 Db maximum gain• 87 degree HPBW• Dynamic range 6.5 Db

• Difference is because of the error in the measurement construction

-40-35-30-25-20-15-10-505

10

-90 -60 -30 0 30 60 90

ANGLE / [Degree]

GA

IN/[d

B]

-40-35-30-25-20-15-10-505

10

-90 -60 -30 0 30 60 90

ANGLE / [Degree]

GA

IN/[d

B]

E-Plane H-Plane


Investigation of Coupling between the Antenna Element and Chassis

• Coupling between 30 degree Chassis and 1 GHz Antennas

• 2 port measurements to measure and

• RF Balun externalization

=

• Antenna elements located at 5 different positions at 3 different orientations on the dipole antenna

12S21S

CouplingS12

erTransform

Measured

SS

12

12

Position 1 and 2 Position 3 and 4 Position 5



S12

-40-35-30-25-20-15-10

-50

540 650 760 870 980 1090 1200f / [MHz]

|S12

|/[dB

]S12

-40-35-30-25-20-15-10

-50

540 650 760 870 980 1090 1200f / [MHz]

|S12

|/[dB

]

Monopole at position 1




S12

-40-35-30-25-20-15-10

-50

540 650 760 870 980 1090 1200f / [MHz]

|S12

|/[dB

]

S12

-40-35-30-25-20-15-10

-50

540 650 760 870 980 1090 1200f / [MHz]

|S12

|/[dB

]





S12

-40-35-30-25-20-15-10

-50

540 650 760 870 980 1090 1200f / [MHz]

|S12

|/[dB

]S12

-40-35-30-25-20-15-10

-50

540 650 760 870 980 1090 1200f / [MHz]

|S12

|/[dB

]

PIFA at position 1

PIFA at position 2



S12

-40-35-30-25-20-15-10

-50

540 650 760 870 980 1090 1200f / [MHz]

|S12

|/[dB

]

S12

-40-35-30-25-20-15-10

-50

540 650 760 870 980 1090 1200f / [MHz]

|S12

|/[dB

]

PIFA at position 3

PIFA at position 4



• The bandwidth of the antenna-chassis system is related to the amount of coupling

• A part of the antenna element is not over the dipole at the first position

• At position 2, it is totally over the dipole, this is because position 2 has more coupling

• Two radiators at 747 and 1000 MHz frequencies

S12

-55-50-45-40-35-30-25-20-15-10-50

540 650 760 870 980 1090 1200f / [MHz]

|S12

|/[dB

]

PIFA at position 5



The coupling of 2 antennas at the same frequency

1. Realization at 747 MHz

• Monopole antenna at 747 MHz is tested on 747 MHz chassis

• The coupling is more if they are at the same frequency as expected. So, more BW is achieved

747 MHz 1 GHz

-40

-35

-30

-25

-20

-15

-10

-5

0

540 650 760 870 980 1090 1200f / [MHz]

747 MHz 1GHz

|S11

|/[dB

]



• 2-port Simulations of Monopole-Dipole and Monopole-PIFA structures at position 2

• Frequency range of 350-1200 MHz

• Very close results

• Simulation approves the measurement

S12 Simulated

S12 Measured

S12 Simulated

S12 Measured


Modeling and Optimizing the Structure

• Monopole Antenna Model

• Series characterization at the first resonance

• Resonance impedance is 34.5 ohm

• corresponds to

L1 C1 = 25.33 nH pF where the frequency is 1 GHz

• A parallel capacity to match the measured results better

TermTerm2

Z=50 OhmNum=2

CC2C=0.629744 pF

RR1R=34.5 Ohm

LL1

R=L=30.4948 nH

CC1C=0.838034 pF

LC1

=ω

freq (540.0MHz to 1.500GHz)

S(1

,1)

S(2

,2)

0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.40.5 1.5

-15

-10

-5

-20

0

freq, GHz

dB(S

(1,1

))dB

(S(2

,2))



TLINTL1

F=1 GHzE=2.69Z=50.0 Ohm

LL2

R=L=16.6 nH

CC1C=6.45 pF

LL1

R=L=4.32 nH

RR1R=275 Ohm

TermTerm2

Z=50 OhmNum=2


S(1,

1)S(

2,2)

0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.40.5 1.5

-30

-20

-10

-40

0

freq, GHz

dB(S

(1,1

))dB

(S(2

,2))

• PIFA Antenna Model

• Parallel characterization at the first resonance

• A very short transmission line

at 1 GHz and a parallel inductance

• Near to the inductance formula 0.75 nH per mm of the probe

8.133λ



• Improved Chassis Model (at 1.09 GHz)

• 30 degree dipole antenna

• Series characterization at the first resonance

• Same resistor value

• Series Capacitance and Inductance are tuned proportionally

TermTerm2

Z=50 OhmNum=2

CC2C=0.58128 pF

LL1

R=L=12 nH

CC1C=2.02 pF

RR1R=27.5


S(1

,1)

S(2

,2)

0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.10.3 1.2

-12

-10

-8

-6

-4

-2

-14

0

freq, GHz

dB(S

(1,1

))dB

(S(2

,2))


Modeling and Optimizing the StructureModeling of Coupling

• Two modeling parameters for the coupling;

• Matching to the Transmission Parameters of the Measurements

• 1-Port measurement from the antenna side when the dipole is shorted (chassis) must give more BW than the antenna alone

• Antenna Positions at position 2 are used

Monopole-Dipole Improved Model

Monopole Antenna Dipole Antenna

RR1R=27 Ohm

LL1

R=L=12 nH

CC1C=2.02 pF

CC2C=0.58128 pF

T ermT erm4

Z=50 OhmNum=4

CC5C=3 pF

T LINT L1

F=1 GHzE=40Z=50 Ohm

CC4C=0.838034 pF

LL2

R=L=30.4948 nH

RR2R=34.5 OhmC

C3C=0.629744 pF

T ermT erm2

Z=50 OhmNum=2



2 port coupling results;

1-port measurement from the monopole side when the dipole (chassis) is shorted;


S(1

,3)

S(2

,4)

0.6 0.7 0.8 0.9 1.0 1.1 1.20.5 1.3

-16

-14

-12

-10

-8

-18

-6

freq, GHz

dB(S

(1,3

))dB

(S(2

,4))


S(2

,2)

0.6 0.7 0.8 0.9 1.0 1.1 1.20.5 1.3

-30

-20

-10

-40

0

freq, GHz

dB(S

(2,2

))



PIFA-Dipole Improved Model

2-port coupling results;


S(1

,3)

S(2

,4)

TermTerm4

Z=50 OhmNum=4

CC2C=0.58128 pF

CC8C=4 pF

TLINTL2

F=1 GHzE=-65Z=50.0 Ohm

RR2R=275 Ohm

LL5

R=L=4.32 nH

CC6C=6.45 pF

LL4

R=L=16.6 nH

TLINTL1

F=1 GHzE=2.69Z=50.0 OhmTerm

Term2

Z=50 OhmNum=2

RR1R=27.5

CC1C=2.02 pF

LL1

R=L=12 nH

PIFA Antenna Dipole Antenna

0.6 0.7 0.8 0.9 1.0 1.1 1.20.5 1.3

-16

-14

-12

-10

-8

-6

-18

-4

freq, GHz

dB(S

(1,3

))dB

(S(2

,4))



• 1-port measurement from the PIFA side when the dipole (chassis) is shorted;


S(2

,2)

0.6 0.7 0.8 0.9 1.0 1.1 1.20.5 1.3

-6

-4

-2

-8

0

freq, GHz

dB(S

(2,2

))

Comparison of the Model and Realization

Antenna Element Alone

Antenna-Chassis Model

Antenna-Chassis Realization

MonopolePIFA

C-Patch

12.3 % 16 % 23 %7.86 % 29 % 25 %

3.48 % 17 % 10 %


Conclusion

• The antennas are tested on large and small ground plane variations

• The chassis is investigated as a dipole

• The couplings between the antenna element and chassis are measured. It is seen that the bandwidth is related to the coupling.

• The equivalent networks of antenna elements, coupled chassis and the coupling mechanism in between are designed

• The chassis and coupling equivalents are improved after tuning the chassis center frequency to 1.09 GHz


Thank you for your attention

angefertigt von cand.-ing. umut bulus bei prof. dr.-ing. k ...umut bulus, 20.03.2008 page 4...

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