A Chip Antenna for cdmaOne† Mobile Phones
by Shoichiro Hirai * , Naoya Arakawa * , Takahiro Ueno * 2 ,Hiroki Hamada * 2 and Koichi Kamei * 2

Mobile phones, one of the representative mobile electronic equipment, are
beginning to be installed with such functions as mailing and imaging as well astransmission and reception of moving pictures. Installation of such additional functions inevitably
requires downsizing and weight reduction of constituting parts in order to maintain the weightand volume of existing equipment. With respect to the whip antenna that is extensively usedconventionally, it has been pointed out that the antenna occupies much space in the casing thus
placing design restrictions. To solve such a situation, Furukawa Electric has developed an ultracompact, high-performance, built-in chip antenna for the 900 MHz band, which can be used
as a main antenna for code division multiple access (cdmaOne) mobile phones. The antennafeatures the use of a high-performance resin material for its dielectric, and it has been confirmedthat the antenna has superior mass productivity and long-term reliability.

ABSTRACT1.

INTRODUCTION

Whip antenna, a representative of external antennas,
with a length corresponding to its resonant wavelengths
is widely used in mobile phones. This type of antenna
must have a storage space in the casing thus placing
restrictions on the sizes of the battery and the circuitry
substrate. In the current situation whereby function
upgrading and design diversification are in progresswith the exploding proliferation of mobile phones, it isobviously required that the main antenna, which is amajor constituting part for mobile phones, should besmall in size as well as low in cost.
In response to such a need for a compact, lowcost antenna for advanced mobile phones, we havesucceeded in developing an ultra-compact chipantenna for CDMA mobile phones of global standard.
The development has been realized based on the coretechnologies of a thermoplastic dielectric resin and ahigh-conductivity, high-strength copper material for
leadframe, both technologies of which the company has
long fostered.
In this report, the features of this ultra-compact chipantenna will be presented.

* Components and Materials Dept., Electronic Components

2.

REQUIRED CHARACTERISTICS, TASKSAND SOLUTIONS

The major developmental tasks are described below.
2.1 Compact and Low-profile Antenna
Tasks of realizing antenna downsizing were constituted
by development of a resin with the most suitabledielectric constant and by how to reduce the size of theradiating conductor while maintaining its desired resonant
frequency.
We have investigated the optimum resin material for
the working frequency of CDMA of 800 MHz to 900 MHz,and furthermore have succeeded in obtaining a compact
antenna of desired frequency through such an approach,whereby a copper alloy material for leadframe is press
worked to form a fine-pitched pattern, which is processed
into a three-dimensional radiation circuit using thedielectric resin thus reducing the length of the antennatransmission line. The use of monopole-type antenna also
helps achieve compactness and high-performance.
The antenna developed here has, as described above,a three-dimensional antenna configuration of copper
conductor which is sandwiched using a thermoplastic
resin, so that it has sufficient strength regardless of its
small thickness. Accordingly, the antenna has satisfactory
resistance against an accidental falling of the mobilephones.

Div.

* 2 Components and Mounting Technology Development Div.,
Ecology and Energy Lab., R&D Div.
† cdmaOne is a registered trademark of CDMA Development
Group.

2.2

Reduction of Resonant Frequency Changes Dueto Ambient Conditions
It is essential for a mobile phone of folding-type toreduce the variation in frequency characteristics of theFurukawa Review, No. 25

2004

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A Chip Antenna for CDMA-ONE Mobile Phones

Thus the simulation technology has become a must in
developing high-value added products such as multiband antennas, ultra-wide band antennas and directivity
controlled antennas, for which demands are increasing inrecent years.
Figures 1 through 3 show some results of simulations,and Figures 4 and 5 show the results of improvement inresonant frequency changes in the folded and unfolded
conditions of folding-type mobile phones, before andafter improvement, respectively. It can be seen that theimprovement of the resonant frequency changes due
to environmental conditions has been achieved usingsimulations.

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antenna as the equipment folds or unfolds. In particular,
the monopole antenna tends to change in terms ofresonant frequency and impedance due to such factors
as the forms of metal casing and circuit substrate and thedistance to the ground plane. Specifically, the resonant
frequency in folded conditions is higher than that ofunfolded conditions. Thus in designing the antenna,
it is required to choose an antenna mounting placeof less interference and to make it unsusceptible toenvironmental changes, i.e., to make it an antenna of
high-isolation characteristics.
In order to meet these requirements, simulation
techniques based on the moment method wereextensively employed to study the designs. The moment
method is one of the numerical analysis methods,
whereby an integral equation is solved by discretization
to obtain an accurate solution in a relatively short time.
In the present analysis, a model for the metal conductors
was discretized using a polygonal element of high degreeof freedom, and current distribution over the model
was calculated by solving Maxwell equations. From thecurrent distribution obtained, antenna characteristics
necessary for performance evaluation are calculated
including the reflection versus frequency, the radiation
pattern, etc.
Simulation are run for antenna characteristics, whereby
the electromagnetic fields are analyzed using the moment
method, significantly reducing the developmental time for
new antennas. Modeling of not only the antenna itself but
also the environmental effects enables quick response
to customers’ needs in the design step for the casing.

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Figure 3

Simulated VSWR vs. frequency characteristics.

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Figure 4Figure 1

Simulated current distribution on
an antenna mounting model.

Simulated changes in VSWR characteristics
in folded and unfolded conditions(before improvement of antenna mounting).

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Figure 5
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Simulated antenna directivity.

Simulated changes in VSWR characteristics
in folded and unfolded conditions(after improvement of antenna mounting).

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A Chip Antenna for CDMA-ONE Mobile Phones

3.

FEATURES

The features of the antenna developed here will be
described in detail below.
3.1 Antenna Structure
Figures 6 and 7 show the appearance and dimensionsof the antenna, respectively. It is generally said that anantenna requires one-quarter wavelength in size, but thesize of the antenna developed here is only one-twentieth
the wavelength, with a volume of 4.8 mm×16.4 mm×1.5mm.
Structural members adopted are as follows.
In order to raise the antenna efficiency, it is necessary
to increase the electrical conductivity of the antennaradiation circuit. To this end, a high-conductivity coppermaterial for leadframe is used as the antenna conductor,and its structure is such that the finely patterned radiation
conductor is covered with a dielectric resin to improvethe durability of the antenna. Lead terminals of J-Lead areused to meet the requirement for surface mounting withhigher density.
Moreover, considering that the environmental issues
that are causing global concerns recently should also betaken into account in the field of electronic parts industry,
we introduced Pb-free plating for the lead terminals thus
responding to such environmental requirements.

3.2 Manufacturing Process
The manufacturing process for the antenna developedhere will be presented below.
This is a continuous, reel-to-reel, product-on-thehoop process covering all the press working of radiation
conductor, insertion molding into resin, and final product.
The details are as follows.
With regard to the manufacture of the radiation
conductor, a high-conductivity, high-strength copper alloy
based on Furukawa Electric’s proprietary technology ispress worked into a fine-pitched radiation conductor. The
stamping accuracy at press working is sufficiently high toachieve a stable form as well as mass productivity.
The radiation conductor thus manufactured iscontinuously inserted into a forming die to be injection
molded with a dielectric thermoplastic resin. The resin
has a small contraction coefficient so that, helped by thedimensional stability of injection molding, contributes agreat deal to achieving a very high degree of dimensional
stability of the final product.
3.3 Radiation Characteristics
The radiation characteristics of the antenna will bepresented below.
Figure 8 shows the reference board, matchingcircuit, and antenna configuration for characteristics
measurement, and Figure 9 the results of VSWR
measurement using this reference board. It can be seen�����

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Figure 6

Appearance of antenna.

Figure 8

Reference board and antenna configurationfor measurement.

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Figure 7

Dimensions of antenna.

Figure 9

Relationship between VSWR and frequency.

Furukawa Review, No. 25

200430A Chip Antenna for CDMA-ONE Mobile Phones�������� ������ �������� � ��������� ����������������� ���� � � ���� ��������� ���� � ����� ������������������������ � ����������� �������������
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Figure 10 Results of radiation pattern and gain measurements.

Table 1

Reliability test items and conditions.

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Results of reliability test.
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CONCLUSION

A chip antenna for cdmaOne mobile phones has beendeveloped. The development was carried out placing
much emphasis on making the antenna mounting spacesaving, highly flexible in casing design, and capableof built-in configurations. An extremely small size has
been realized helped by the investigations of molding
resin materials together with the adoption of a threedimensional radiating circuit, and the antenna has been
confirmed to have good long-term reliability.
Hereafter, we plan to develop multi-band antennas ofdual- and triple-band type using the same manufacturing
technologies, thus promoting expansion of the productlineup.

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Each test was preceded by a series of pre-processing
comprising a humidity-absorbing process of 85°C/RH85%×168 hr and three repetitions of a reflow process
for solder melting of 30~40 sec duration at 230°C or
higher with 250°C peaks. Subsequently, the electricalcharacteristics were measured using our proprietary
instruments including a shielding room.
Table 2 shows the results of the evaluation. As shownin the table, the initial characteristics scarcely changedby the tests, thus confirming that sufficient reliability has
been achieved. Incidentally, initial characteristics before
the tests were as follows.
Averaged resonant frequency: 903 MHz
Averaged bandwidth (VSWR=2): 100 MHz or more�� � �� ����� � �������� �� �����

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���� ������� � �� ����� � �������� �� ����that the bandwidth for VSWR of not greater than 2.0 is
50 MHz --no doubt a wide bandwidth when its extremely
small size is considered.
Figure 10 shows the results of gain and directivity
measurements. It can be confirmed that the average gain
is high and the directivity is omnidirectional, satisfactorily
meeting application requirements.

4.

RELIABILITY EVALUATIONThe results of reliability evaluation of the antenna will bepresented below.
Table 1 shows the items and conditions of evaluation.
The evaluation included five items of low-temperaturestorage, high-temperature storage, high-temperature andhigh-humidity storage, heat shock, and salt spray test.

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