Mobile Phone Antenna

1

THE CHINESE UNIVERSITY OF HONK KONG

Design of Mobile Phone Antenna

Yip Wah Chun

香港中文大學電子工程學系

DEPARTMENT OF ELECTRONIC ENGINEERING

2

Design of Mobile Phone Antenna

Author: Yip Wah Chun

Student I.D.: 03608183

Supervisor: Professor K.L. Wu

Associate Examiner: Professor K.N. Leung

A project report presented to the Chinese University of Hong Kong

in partial fulfillment of the Degree of Bachelor of Engineering

Department of Electronic Engineering The Chinese University of Hong Kong

April, 2007

I

Abstract

In recent years, the demand for small and mobile communication devices,

especially the mobile phone, has grown rapidly. Devices having internal

antenna is a trend and is required for such applications Antenna size is a major

factor that limits device miniaturization. To decrease the size, antenna design

is base on microstrip antennas and planar inverted-F antennas (PIFA) which

have been used for handheld wireless devices because these antennas have

low-profile geometry and can be embedded into the mobile phone.

Nowadays, mobile phones are not only for voice communication but they are

required for operation in more than one frequency band.

Dual-band and tri-band phones have been now become a standard because of

the multiple frequency bands used for wireless applications.

Reducing antenna size generally degrades antenna performance. It is

therefore important to also examine the effect on the size reduce and

parameter tradeoffs for reducing the size. In the handheld environment,

antennas are mounted on a small ground plane. Ground plane size effects on

antennas are investigated

II

Acknowledgements

I would to acknowledge Professor Wu Ke Li on the advice on the project. He

has a deep knowledge on electromagnetic wave that I can gain more

knowledge on it. Through the project, I learn how to use simulation tools to

design the antenna. All these meetings are a great help for this project.

I would to thank tutor Lam Fuk Ming who give many advice on the project.

Also, I have to thanks all the staffs in Microwave Laboratory for all the

supports.

III

Content

Abstract .......................................................................................................................... I

Acknowledgements....................................................................................................... II

Content.........................................................................................................................III

Chapter 1- Introduction..................................................................................................1

1.1 Introduction......................................................................................................1

1.2 Thesis Outline ..................................................................................................2

Chapter 2 - Antenna of Mobile Unit ..............................................................................3

2.1 Small mobile phone antenna............................................................................3

2.1.1 Miniaturization..............................................................................................4

2.2 Bandwidth ........................................................................................................5

2.3 Reviews of Mobile Phone Antennas ................................................................5

2.4 Monopole .........................................................................................................6

2.5 Normal Mode Helical Antenna ........................................................................7

2.6 Meander Line Antenna.....................................................................................8

2.7 Inverted-L Antenna (ILA)................................................................................9

2.8 Inverted-F Antenna (IFA) ..............................................................................10

2.9 The meander Planar Inverted-F Antenna .......................................................12

Chapter 3 – Design of Antenna....................................................................................13

3.1 Overviews ......................................................................................................13

3.2 Design Tools ..................................................................................................13

3.3 Design Consideration.....................................................................................14

3.3.1 Location of Antenna............................................................................15

3.3.2 Ground plane effect.............................................................................16

3.3.3 Antenna Height Effect.........................................................................19

IV

Chapter 4 – Antenna Simulation ..................................................................................20

4.1 Dual band Mobile Phone Antenna .................................................................20

4.1.1 Return loss ..........................................................................................21

4.1.2 Current Distribution ............................................................................22

4.1.3 Radiation Pattern.................................................................................24

4.2 Triple band Antenna.......................................................................................25

4.2.1 Return Loss .........................................................................................26

4.2.2 Current Distribution ............................................................................27

4.2.3Radiation Pattern..................................................................................29

Chapter 5 – Antenna Implementation ..........................................................................31

5.1 Antenna Fabrication .......................................................................................31

5.1 Experimental Setup – Network Analyzer ......................................................33

5.2 S11 .................................................................................................................34

Conclusion ...................................................................................................................35

Reference .....................................................................................................................36

1

Chapter 1- Introduction 1.1 Introduction

In the mobile communication, in the past decade, the industry has grown

significantly. In the past, the mobile unit has only for voice communication, it

has changed and more band and applications are need in a mobile phone

which may lead the mobile phone has multiple antenna.

In the mean time, the most of the mobile phone has been in internal antenna

elements instead of external whip and helix antennas used previously.[1] Also,

the space is very limited for antennas inside the casing of a mobile unit,

antennas with as small size as possible are needed. One great challenge in

the antenna development is to obtain compact antenna elements with

sufficient bandwidth and high efficiency.

We have to male the trade of between the different properties of the antenna

such as the size, bandwidth, gain, etc.[2] Besides, universal antenna elements

cannot be realized because the antenna performance depends strongly on the

size of the metal parts of the device and the location of the antenna on it.

2

1.2 Thesis Outline

In this chapter, there is a brief introduction on mobile phone issue is stated on

discussed.

In chapter 2, there is a review on the mobile phone antenna, discussion on

different type antenna on mobile phone.

In chapter 3, design issues on the mobile phone antenna are investigated and

it showed how they affect the antenna.

In chapter 4, a design on the mobile phone antenna is mention and simulation

result is shown.

In chapter 5, it showed the antenna fabrication and measurements on the

antenna are carried out.

3

Chapter 2 - Antenna of Mobile Unit

2.1 Small mobile phone antenna

In recent years, the mobile cells market has been growing rapidly all over the

world. One of the trends in mobile phone in the past few years has been to

reduce the size and weight of the mobile phone. This remarkable reduction in

the unit’s size has sparked a rapid evolution of the antennas used for mobile

phone.

Hence, the design of antennas for small mobile terminals is becoming more

challenging. The antennas are required to be smaller and smaller and their

performances have to be maintained. However, usually a degradation of the

gain and bandwidth are observed when the antenna’s size is reduced.

Furthermore, more than one antenna will be implemented in a mobile phone

as more applications are required today. As a result, the design of two or more

antennas on a small mobile phone is more challenging compared to the design

of a single conventional antenna in the mobile phone. [3]

4

2.1.1 Miniaturization

To decrease the size of an antenna, the resonant frequency remains the same

even though the antenna size is reduced. Some of the parameters that may

suffer are:

1 Reduced efficiency (or gain)

2 Shorter range

3 Smaller useful bandwidth

4 Increased sensitivity to external factors

There are several means for miniaturization.

1 By loading the antenna in a way that the self-resonance is obtained when the

antenna volume is smaller than that of a basic structure.

2 By increasing the effective resonator length by bending the structure

according to some geometrical configuration, e.g. meandering.

Several techniques can be applied to further reduce the antenna size.

However we have to trade off the effect by applying different miniaturization

methods.[4]

5

2.2 Bandwidth

For a small antenna, the term bandwidth typically refers to the impedance

bandwidth. The antenna should have an adequate bandwidth covering the

frequency range used by the required wireless communication system. The

requirements for operating frequency and bandwidth are different for each

system. Typically, the impedance bandwidth in cellular systems could be

defined as the return loss of Lretn > 6 dB for the whole operating frequency

range. [5]

2.3 Reviews of Mobile Phone Antennas

For the mobile communication systems in 1980s (the earliest mobile

communication), the typical mobile phone was nearly 600cc in volume and

approximately 850g in weight. The antenna used for the first phone was a half

wavelength monopole antenna. After many years of evolution, the volume for

the mobile phone had been reduced to less than 60cc and a weight of less

than 60g around 2000. it can see that the built-in antennas are more preferable

than the half-wavelength monopole antenna.

6

2.4 Monopole

The quarter-wavelength monopole antenna is the fundamental mobile antenna

and has a simple structure as shown in Figure 2.1. However, a

quarter-wavelength monopole antenna caused large leakage currents to the

terminal case compared to the half-wavelength monopole antenna [6].

For a half-wavelength monopole, the maximum current amplitude occurs

around the center of the monopole therefore current amplitude around the feed

point (between the monopole and the terminal case) is small. However, for a

quarter-wavelength monopole the maximum current amplitude occurs around

the feed point and large current flows into the terminal case. Due to the

leakage currents, the length of the terminal case significantly changes the

radiation characteristics of an antenna.

Moreover, the 3/8 or 5/8 wavelengths monopole antennas have been

employed for mobile terminals as they have the appropriate input impedance

for matching to the feeding line and yet the current flow on the terminal case is

very small. This antenna is also named as the “whip” antenna.

7

Fig 2.1 - 1/4-wavelength monopole antenna

2.5 Normal Mode Helical Antenna

In the normal mode, the dimensions of the helix are small compared with the

wavelength. The far field radiation pattern is similar to an electrically short

dipole or monopole. These antennas tend to be inefficient radiators and are

typically used for mobile communications where reduced size is a critical factor.

A Tesla coil secondary coil is also an example. Figure 2.2 show a structure of a

helix

Fig 2.2 - Geometrical configuration of a helix

8

2.6 Meander Line Antenna

This antenna define as an antenna with the wire folded back and forth where

resonance is found in a much more compact structure than can otherwise be

obtained.

For example we can shorten a monopole by using a printed meander pattern

instead of a helical as shown in Figure 2.3. Meander line antenna is also a

physically small but electrically large antenna.

A planar and compact meander line antenna has been studied [7]. Multi-band

characteristics can be accomplished by connecting two or more λ/4 meanders

in parallel with each being tuned to its own frequency as shown in Figure 2.4.

Fig 2.3 Meander printer antenna

9

Fig 2.4 Dual-band meander line antenna.

2.7 Inverted-L Antenna (ILA)

The inverted-L antenna is an end-fed short monopole with a horizontal wire

element placed on top that acts as a capacitive load. Figure 2.4 shows the

structure of the inverted-L antenna. The inverted-L antenna is an attractive

alternative because of its simple layout. The design is uncomplicated and can

be easily manufactured with low cost materials.

Additionally, many of the electrical characteristics of the inverted-L are similar

to those of the well understood short monopole.

The ILA has low input impedance as its input impedance is equal to that of the

short monopole plus the reactance of the horizontal element closely placed to

the ground plane.

10

Fig. 2.4 – Structure of Inverted-L antenna

2.8 Inverted-F Antenna (IFA)

Most of the new mobile terminals (e.g. GSM phones) have built-in antennas

which are not extruded from the terminal’s exterior. Generally, the very top of

the phone is not the best position to place the antenna because the antenna

element should be kept away from the user to avoid unnecessary losses. Also,

the antenna should not be placed too low on the back of the phone either as

such a position will increase the antenna’s losses due to the users’ hand.

Therefore, the surface on the upper back of the phone is a preferable position

to place the built-in antenna. The well known built-in antennas i.e. Inverted

F-antenna (IFA) and PIFA have been widely used in most of current mobile

terminals.

The IFA is originally transformed from an inverted-L antenna (ILA) which

consists of a short monopole as a vertical element and a wire horizontal

11

element attached at the end of the monopole. The ILA is a low profile antenna

as the height of the vertical element is usually much less than a wavelength.

The horizontal element normally has a length of about a quarter wavelengths.

The planar version of the inverted-F antenna, the planar inverted-F antenna (PIFA),

meets the specifications which are required in a reduced size environment as shown in

figure.2.5.

The common characteristics of the PIFA have been analyzed in [8] The

shorting pin is positioned at the corner of the planar element to yield a

maximum reduction in the antenna’s size. The narrower the shorting plate

width, W, the lower the resonant frequency of the PIFA. The resonant

frequency (f) of the PIFA can be determined from the equation below

f =c/ 4(L1+L2) (3.1)

where L1 is the width of PIFA, L2 is the length of PIFA and c is the speed of light

in free space.

Figure 2.5 – Structure of Planar Inverted-F Antenna

12

2.9 The meander Planar Inverted-F Antenna

One other variation of the PIFA is introduced with the meander like structure, it

has a further reduction in size while still maintaining adequate bandwidth. The

bandwidth still maintained and the size is only an eighth of a wavelength long.

The meander PIFA is modification of the conventional PIFA design that is

slightly reduced in size from the conventional PIFA. It uses several slits cut

laterally in the PIFA radiating element. These slits effectively act to increase

the electrical length of the antenna and allow for reduced overall antenna

volume.

13

Chapter 3 – Design of Antenna

3.1 Overviews

The mobile phone antenna to be designed is based on the structure of the

Planar Inverted-F Antenna. The idea is to cut slot on the planar element of a

PIFA, sp that the antenna can work as a multi-band PIFA. As shown in figure

3.1, the basic principle is that the longer arm resonates at low band whilst

shorter arm resonates at high band.

Figure 3.1 – Structure of a dual band antenna

3.2 Design Tools

The Cellular PIFA was simulated using a commercial 2.5D Method of Moments

code (IE3D). The reason to use IE3D is that It use the moment method codes

use an integral equation formulation combined with a matrix method to solve

the antenna characteristics. The surface nature of the integral equation

14

formulation makes it particularly suited to solving wire and surface geometries.

Moment method codes have the advantage of typically being computationally

faster than other numerical analysis methods

3.3 Design Consideration

The dimensions of the phone may vary a lot depending on the handset design.

In current mono block mobile phone, the typical length is in the range of 80-

140 mm, the width in the range of 40-60 mm, and the thickness a few

millimeters. For the phones with a slider, the phone dimensions change in

different use positions.

Beside, antenna location and antenna height can affect the performance of the

antenna. The bandwidth and efficiency can be varied with changing the above

parameters.

A rough design of the antenna is designed as follow: Different parameter of the

antenna is studied then.

15

Figure 3.2 – Structure of the mobile phone antenna (dimension in mm)

3.3.1 Location of Antenna

The location of the antenna is studied to find the best position to locate the

antenna.

The antenna’s position is varied from top of the antenna to see its effect on the

performance of the antenna. Its effect on the bandwidth of antenna is plotted

as follow:

16

Location of Antenna

0

1

2

3

4

5

0 10 20 30 40 50

Location (mm)

Ban

dWid

th (

%)

Frequency-900MHz

Frequency-1800MHz

Figure 3.3 – Effect of different location of antenna

3.3.2 Ground plane effect

It is studied that most of the antennas used in current mobile phones are small

unbalanced antennas for which the ground plane is an important factor. This

can includes inverted-F antennas (IFA), planar inverted-F antennas (PIFA),

and their derivatives. When it is attached to a relative small finite ground plane,

some of the properties of these antennas can be very different from those of

the same antennas on a large or infinite ground plane.

There is a strong influence of the mobile size on the antenna parameters. The

effect of a small ground counterpart has also been noticed in [5] in a different

17

context.

Figure. 3.4 shows the results for a length of the mobile phone antenna ground

plane ranging from 80 mm to 150 mm. It is noticed that a strong effect which.

the impedance bandwidth of the antennas rises until the mobile reaches a

certain length

Ground Plane Effect

0

1

2

3

4

5

6

7

8

9

80 90 100 110 120 130 140 150

Ground Plane (mm)

rel.

Ban

dwid

th -

10dB

(%

)

Frequency-900MHz

Frequency-1800MHz

Figure 3.4 Effect of ground plane on bandwidth

18

Beside, its effect on the resonant frequency of the antenna is showed in figure

3.5, it can see that the resonant frequency is not much affected by the size of

the ground.

Effect on Fr

0

500

1000

1500

2000

80 90 100 110 120 130 140 150

mm

Freq

uen

ct(M

Hz)

1800

900

Figure 3.5 Effect of ground plane on resonant frequency

19

3.3.3 Antenna Height Effect

It is known that in PIFA, the antenna height has a effect on the performance of

the antenna. Figure 3.6 shows that the antenna height effect on the bandwidth

of the antenna. It is noticed that as antenna height increase the bandwidth

increase.

Effect of Antenna Height

0

1

2

3

4

5

6

2 3 4 5 6 7 8

Height (mm)

Ban

dwid

th (

%)

Frequency-900MHz

Frequency-1800MHz

Figure 3.5 – Antenna height effect on bandwidth

20

Chapter 4 – Antenna Simulation

4.1 Dual band Mobile Phone Antenna

After studied the factors that affect the antenna, a dual band mobile phone

antenna is designed. The dimension of the ground of the antenna is 40mm ×

110mm, the size of the antenna part is 40mm × 30mm, with a height of 7mm. Figure 4.1

show the top view of the mobile phone antenna and figure4.2 show the slide view of the

mobile phone antenna

Figure4.1 Top view of the antenna

Figure 4.2 Side view of the antenna

21

4.1.1 Return loss

The return loss is plotted in figure4.3, it can show that the antenna work on the

desired frequency band, 900MHz and 1800MHz.

Figure 4.3 Return loss of the dual band mobile phone antenna

For the 10bB bandwidth efficiency, at 900MHz, the bandwidth is 8.7%, at

1800MHz, the bandwidth is 3.8%.

22

4.1.2 Current Distribution

The vector and average current distribution of the antenna at 900MHz and

1800MHz are showed in figure 4.4 and they are compared with that in 500MHz

and 2100MHZ

Figure 4.4a Current distribution at 900MHz

Figure 4.4b Current distribution at 1800MHz

23

Figure 4.4cCurrent distribution at 500MHz

Figure 4.4dCurrent distribution at 2100MHz

It is obvious that the current distribution is denser in the operating band.

24

4.1.3 Radiation Pattern

The radiation patterns are shown is figure 4.5

Figure 4.5a Pattern view of the antenna at 900MHz

Figure 4.5b Pattern view of the antenna at 1800MHz

25

4.2 Triple band Antenna

The antenna is used the Dual inverted-F antenna geometry together with a

meander structure to obtain the desired frequency range.

The structure of the antenna is shown in figure 4.6

Figure 4.6 structure of the antenna

Part Length (mm) Width (mm)

a 30 9

b 30 6

c 30 6.5

d 29 6.5

e 28.8 6

26

4.2.1 Return Loss

The return loss is plotted in figure4.7, it can show that the antenna work on the

GSM band and has a third band at 2.5GHz

Figure 4.7 Return loss of the triple band antenna

For the 10bB bandwidth efficiency, at 900MHz, the bandwidth is 7.6%, at

1800MHz, the bandwidth is 4.8%. For the third band, it has a 6dB bandwidth

which is 2.5%.

27

4.2.2 Current Distribution

The vector and average current distribution of the antenna at 950MHz and

1800MHz and 2450MHz are showed in figure 4.4 and they are compared with

that in 500MHz



28



It can see that the current is denser in the operating frequency.

29

4.2.3Radiation Pattern

The pattern views are compared in figure 4.9

Figure 4.9a Pattern view of the antenna at 930MHz


30


31

Chapter 5 – Antenna Implementation

After the antenna is simulated as shown in Chapter 4, the antenna is fabricated

using fr4 as the material. It has 0.8mm thick with a dielectric constant 2.2.

5.1 Antenna Fabrication

The fabrication of the antenna is carried out in the darkroom and the fabricated

antenna is shown in figure 5.1.

Figure 5.1a Dual band antenna

Figure 5.1b Top view of dual band antenna

32

Figure 5.1c Triple band antenna

Figure 5.1d Top view of triple band antenna

33

5.1 Experimental Setup – Network Analyzer

R3767CG Network Analyzer is a microwave measurement system, which can

determine the S-Parameters for a given two-port device. The S-Parameter is in

the form of a four scattering matrix and S11, S12, S21, S22 have both

amplitude and phase values.

Figure 5.2 R3767CG Network Analyzer

For the test equipment, it may exist some errors and alters the measurement

result. Therefore, before taking the measurement, an error correction process

should be performed by Calibration. This calibration is to let the Network

Analyzer measure the standards (i.e. open circuit, short circuit and precision

load impedance) provided in the Calibration Kit.

This calibration can remove directivity, source match and reflection tracking

from reflection measurements

34

5.2 S11

The return loss of the dual band antenna is shown in figure5.3 , it is noticed

that the resonant frequency has a shift to the desired frequency band.

Figure 5.3 Return loss of antenna

The error can be due to the fabrication of the antenna is not perfect enough.

35

Conclusion

In conclusion, in designing an antenna for mobile phone, there are many

factors that need to be considered. Today, mobile phone has many types, such

as mono block, slide, fold and swivel, So far it has been impossible to make

the universal antenna (module), because different form factors have different

requirements on antenna shape and placemen

The antennas suggested in this project can work on dual band or triple band

which is suitable for GSM and some application.

Also, the mobile phones are requiring more and more application beside the

voice communication, and it would become more complicated and challenging.

36

Reference

[1] L. Setian, Practical Communication Antennas with Wireless Applications,

Prentice Hall PTR, New Jersey: 1998.

[2] Design Guide for Wireless Device Antenna Systems, Centurion Wireless

Technologies, Inc, 2000

[3] Multi band, multi antenna system for modern mobile terminal, Zhinong

Ying and Johan Anderson, IEEE 2003

[4] O. Lehmus, Miniaturization methods of handset antennas, Master’s

Thesis, Helsinki University of Technology, Radio Laboratory, Espoo,

Finland, Feb. 1999, 99 p.

[5] J. Toftgård, S. N. Hornstleht, and J. B. Andersen, “Effects on portable

antennas of the presence of a person,” IEEE Trans. Antennas Propagat.,

vol. 41, no. 6, June 1993, pp.739-746.

[6] K. Hirisawa and M. Haneishi, Analysis, Design, and Measurement of

small and Low-Profile Antennas, Artech House, Boston: 1992.

[7] A.B. Smolders, Microstrip Phased-Array Antennas: A Finite-Array

Approach, Thesis Report, Endhoven University of Technology, 1994,

[8] K. Hirasawa, and M. Haneishi, Design, and Measurement of Small and

Low-profile Antennas, MA: Artech House, 1991.

Documents

Mobile Phone Antenna