Ultra-Compact Chip Antenna for the 2.4~2.5 GHz Bandby Shoichiro Hirai *, Naoya Arakawa *, Takahiro Ueno *2,
Hiroki Hamada *2, Isao Tomomatsu *3 and Yoichi Iso *4

Recently the development of information-intensive society around us is quite
remarkable, making many innovative systems indispensable for our daily lives.
There are, e.g., the explosive development and diversification of mobile phones, wirelesscommunications technologies and car navigation systems for automobiles, and the domestic
penetration of short-distance wireless communications equipment that are in conformity with
Bluetooth or IEEE 802.11a and 11b. Antenna is one of the key components supporting thewireless technologies. Furukawa Electric has developed a high-performance ultra-compact chipantenna for the 2.4~2.5 GHz band. The antenna features the use of a functional resin material forits dielectric, and has been confirmed to be suitable for mass production ensuring high long-term
reliability.

ABSTRACT1.

INTRODUCTION

Wireless communications in conformity with Bluetooth,IEEE 802.11b, etc. are generally used for handing overof data between various electronic equipment such as
notebook PCs, mobile phones, headsets, PDAs (Personal
Digital Assistant), and digital cameras. For wider
acceptance of these equipment by society, it is necessary
to make them small in size and low in cost.
In response to these needs, Furukawa Electric has
succeeded in developing an antenna, one of the key
components for communication equipment, based on
the long-fostered core technologies of high-permittivity
thermoplastic resins and high-conductivity, high-strength
copper alloys for leadframes. This paper reports on thecharacteristics of this ultra-compact chip antenna.

2.

DEVELOPMENT TASKS OF COMPACTCHIP ANTENNA

Development tasks for this antenna are described below.
2.1 Downsizing of Antenna
The role for an antenna is to radiate high-frequency
energy generated in electronic circuits into the space*

Components and Materials Dept., Electronics Components Div.
Components and Advanced Interconnect Technologies
Dept., Ecology and Energy Lab.
*3 Nano-Technology Center, Ecology and Energy Lab.
*4 FITEL Network Lab.
*2

as electromagnetic waves, and, vice versa, to gather
electromagnetic waves in the space converting them as
high-frequency energy into the electronic circuits. Thus aresonant antenna that resonates at a specific frequency
is very efficient since it can induce large currents in thecircuit.
The wavelength at 2.45 GHz is calculated to be about
12 cm, so that a linear antenna that resonates at thisfrequency to induce a large current has to have anelement 12 cm in length, or at least 3 cm for a quarter
wavelength. When an antenna is to be used, however,in mobile equipment such as mobile phones, headsets,
and PDAs, it should be as compact as possible in order tosave space and improve design flexibility.
2.2 Omnidirectional Radiation and High Gain
The intensity of electromagnetic wave radiated froman antenna changes, even at the same distance fromthe antenna, according to the direction. This is called
directivity of antenna. The directivity of an antenna formobile applications should be omnidirectional, since thedirection of reception or transmission depends on the use
conditions of the mobile equipment.
Mobile equipment such as mobile phones, PDAs, andnotebook PCs are carried around everywhere, so that low
power consumption is one of the important characteristicsof these equipment. Accordingly, every electronic
component used should be as low as possible in power
consumption. Antennas are also required to efficiently
radiate electromagnetic waves using small power, i.e., tohave a high radiation gain.

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Ultra-Compact Chip Antenna for the 2.4~2.5 GHz Band

2.3 Broad Bandwidth
Basically the bandwidth of an antenna decreases as
its size is reduced. When mounted on equipment, theresonant frequency of an antenna changes through the
influence of the environment. Thus narrow bandwidth
raises a practical problem of difficult adjustment. Mobile
equipment of today are rapidly increasing their mounting
density accompanied by size reduction, requiring
every component to be small in size. Consequently, it
is essential that the downsizing of an antenna is done
while maintaining its wide bandwidth so as to cope withfrequency changes due to influence of the mounting
environment.
2.4 Cost Reduction
Recently communications equipment are coming downin price day by day. It is necessary therefore that our
products meet the customers’ needs for cost reduction,satisfactorily maintaining stable performance and mass
producibility.

3.

PRODUCT FEATURES

Features of the antenna developed here will be describedin detail below.
3.1 Antenna Structure
Figure 1 shows an appearance of the antenna and Figure
2 its outer dimensions. Whereas it is generally said thatan antenna size should be a quarter wavelength, the sizeof the antenna developed here is no more than one-tenthwavelength.

Figure 1

Appearance of antenna.

8.8

0.4

2.9

1.4

0.4

0.7

0.7

1.45

0.7

8

Unit: mmFigure 2

Outer dimensions of antenna.

Table 1Comparison of antenna volume.

Resin

Antenna volume

Conventional (permittivity=3)50.40 mm3

New resin used here

16.24 mm3

The materials employed in the antenna structure are as
follows.
To increase the efficiency of an antenna, the electricalconductivity of antenna’s radiation circuit should be
improved. We have employed a high-conductivity copper
alloy for leadframes as the conductor, and sheathed
it using a high-permittivity thermoplastic resin that thecompany has proprietarily developed.
Table 1 shows a comparison of antenna volume
between the resin used here and the one having apermittivity of three. It can be seen that that the antennavolume has been reduced to about one third. Meanwhile,the thermoplastic resin used here has both heat
resistance and heat-and-humidity resistance sufficient for
in-vehicle use in automobiles, thereby making the antenna
available for all application environments.
Moreover, the antenna uses lead-terminal structures
unlike conventional ceramics chip antennas. This leadterminal portion relaxes the stress caused by the
expansion and contraction due to the difference in thermal
expansion coefficient between the resin and mounting
board, thus improving the reliability of soldered joints after
surface mounting. This provides the product with superior
resistance against heat shock.
In addition, whereas much has been talked about
environmental issues globally in recent years, theseissues have to be taken into consideration with regard
to electronic components also. Therefore, in response
to such environmental issues, we have adopted a 100% Sn-plating for the lead-terminal portion, thus realizing
Pb-free plating.
3.2 Radiation Characteristics
As mentioned previously, the antenna developed here
has adopted a structure such that, in order to obtainhigh-efficiency as well as ominidirectional directivity,
the high-conductivity conductor is sheathed using ahigh-permittivity thermoplastic resin that the company
proprietarily developed. A special meander configuration
was adopted for the conductor that significantly
influences radiation characteristics. A variety of conductor
configurations were evaluated confirming that suchfactors as the aspect ratio of capacitive loading element
and the spacing and layout of wires strongly influence
the characteristics. Subsequently basic design was
carried out using simulation techniques to determine theoptimized meander configuration. Figure 3 and Figure 4
show an electric field distribution and radiation directivity,
respectively, both are the results of simulation.
Measurement results of antenna characteristics will be
described next.
Figure 5 shows the reference board for antenna

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Ultra-Compact Chip Antenna for the 2.4~2.5 GHz BandZ+

Antenna

2.3

XY-

X+

Y+

34

49

Z

GND
17

Figure 5

Figure 3

Schematic of reference board for evaluationof antenna together with antenna layout.

3.0

Typical electric field distribution.

2.8
2.6

90

2.4

VSWR

120

60

150

2.2
2.0
1.8
1.6
1.4

30

180

1.2
1.0
2.25

2.3

2.35

2.4

0

210

Figure 6

330

240
270

Figure 4

2.45

2.5

2.55

2.6

2.65

Frequency (GHz)XY-plane

VSWR vs. frequency.

dBi

X-

10

300

V-XY

H-XY

Ave. [dBi]

0.3

-10.3

Max. [dBi]

2.4

-5.2

0
-10

Typical radiation directivity.

-20
-30

characteristics evaluation together with antenna layout,
and Figure 6 the result of VSWR measurement. It canbe seen that the antenna has a broad bandwidth of
more than 200 MHz for a VSWR of 2. This bandwidthis about three times the Bluetooth band of 2400~2480
MHz, so that it is sufficiently broad to assure the standard
bandwidth even when subjected to the influences of thecasing as well as human body.
Figure 7 shows the results of the gain and directivity
measurements. It can be confirmed that the antenna has
high gain and omnidirectional directivity, satisfactorily
meeting the development tasks.
Meanwhile, the radiation efficiency of the antenna isassuredly 70~80 %.
3.3 Feeding Configuration
It is desirable that the antenna has sufficient flexibility,
although it is under the severe constraint of equipment
design, in mounting on the equipment. The antenna

Y-

Y+

-40

V-XY
X+

Figure 7

H-XY

Radiation pattern.

developed here has been designed to enable configuring
two types of feeding, i.e., monopole type and inverted-F
type, which can be selected at the time of mounting to
improve mounting flexibility.
The two types of feeding configuration are shown in
Figures 8 and 9, respectively. One of the two terminals
is to be used for monopole feeding, and the other for
inverted-F feeding. The two types of feeding can besuitably selected according to the form of GND and therelative position of antenna with respect to GND, thereby

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Ultra-Compact Chip Antenna for the 2.4~2.5 GHz Band

Pin 3: Open

Antenna (SF2450)

L

0.9

Pin 1: Feed-in

34

49

Pin 2: OpenTo feeding circuit
through 50Ω feeder

Figure 817

Monopole-type feeding.
Pin 3: OpenGND

Figure 10 Schematic of reference board for evaluation of
feeding configuration together with antenna layout.

500

Pin 2: Feed-in

To GND on substrate

Bandwidth (MHz)400

Pin 1: Ground

300

100

To feeding circuit
through 50Ω feeder

Inverted-F type feeding.

3.4 Manufacturing Process
The manufacturing process for the antenna developed
here is described below.
The process permits continuous manufacturing of
the product in the form of hoop on a reel-to-reel basis,covering the patterned sheet conductor, insertion molding
into resin, and the final product. Details are as follows.
The patterned sheet conductor is manufactured
from a high-conductivity, high-strength copper alloy for
leadframes of Furukawa Electric’s proprietary materialusing press stamping. Whereas, as mentioned before,
the meander configuration of the radiating conductor
significantly influences the characteristics, the accuracy

0

1

2

3

4

5

6

7

8

9

Antenna-to-GND distance (mm)Figure 11 Relationship between bandwidth (VSWR=2)
and antenna-to-GND distance.
100
90

Radiation efficiency (%)

achieving high efficiency. Figure 10 shows the referenceboard used for feeding configuration evaluation together
with antenna layout. Using this board the changes incharacteristics of monopole feeding and inverted-F
feeding were measured as the distance L between theantenna and GND was changed. Figure 11 shows therelationship between the distance and bandwidth andFigure 12 the relationship between the distance andefficiency, respectively.
Which of the two feeding configuration is more efficientdepends on the antenna installation conditions in eachequipment, so that adjustment and evaluation should be
carried out equipment by equipment for final confirmation.

Monopole feeding

200

0Figure 9

Inverted-F feeding

Inverted-F feeding

80
70

Monopole feeding

60
50
40
30
20
10
0

0

1

2

3

4

5

6

7

8

9

Antenna-to-GND distance (mm)Figure 12 Relationship between radiation efficiency
and antenna-to-GND distance.

of press stamping is sufficiently high, achieving stableconfigurations as well as mass producibility.
The patterned sheet conductor thus manufactured iscontinuously inserted into forming mold, and is sheathedwith a high-permittivity thermoplastic resin using injection
molding. The resin has a low contraction ratio, and thus
contributes to achieving, helped by the dimensional
stability of injection molding, a very high degree ofdimensional stability in the final products.

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Ultra-Compact Chip Antenna for the 2.4~2.5 GHz Band

Table 2
No.

Table 3

Reliability test conditions.

Test item

Conditions

Time

1

Low-temperature storage-40°C

1000 hrs

2

High-temperature storage+90°C

1000 hrs

85°C·85 %1000 hrs

High-temperature and3high-humidity storage

4

Temperature and humidity cycling

5

Heat shock-25~+85°C-40°C↔+85°C,
30 min each

10 cycles
1000 cycles

No.

Results of reliability tests.

Test item

Change after test
Resonant frequency Bandwidth (VSWR=2)

1

Low-temperature storage±1 % or less

5 % decrease or less2

High-temperature storage±1 % or less

5 % decrease or less

±1 % or less

5 % decrease or less

±1 % or less

5 % decrease or less

±1 % or less

5 % decrease or less3
4
5

High-temperature andhigh-humidity storage
Temperature andhumidity cycling
Heat shock

+85°C

+25°C
-10°C
2.5h

3h

94 %

2.5h 2.5h

89 %

3h

2.5h

94 %

89 %

2h

3.3h

3h

94 %

Figure 13 Conditions for heat and humidity test.

At the end of the process, the molded products in theform of hoop are separated one by one and are containedin trays and the like. But they are also available in theform of tape carrier for surface mounting.
To summarize, the manufacturing process for theantenna developed here is a continuous manufacturingmethod ranging from patterned sheet conductor to
injection molding. The process is amply compatible withthe current hoop-forming techniques, necessitates no
dedicated instruments, has superior mass producibility,
and thus enables low-cost production.

4.

RELIABILITY EVALUATIONThe results of reliability evaluations for the antenna are
explained below. The conditions for evaluations areshown in Table 2 and Figure 13. The evaluations werecarried out in terms of low-temperature storage, hightemperature storage, high-temperature and high-humidity
storage, temperature and humidity cycling, and heatshock. The heat-shock test was preceded by a series of
pre-processing comprising a humidity-absorbing processof 85°C/RH85 % × 168 hrs and three repetitions of reflow
process at 230°C containing 250°C peaks of 30~40 sec
duration.

The results of evaluations are shown in Table 3. The
electrical characteristics were measured using our
proprietary instruments.
As shown in the table, the characteristics scarcely
changed after tests, thus confirming that sufficientreliability has been achieved. Meanwhile, initialcharacteristics before the tests were as follows:
Averaged resonant frequency:
2465 MHz
Averaged bandwidth (VSWR=2): 260 MHz or more

5.

CONCLUSION

As explained above, the antenna developed here
has a number of features. It is compact, so that alimited space suffices to mount the antenna onto highdensity mounted mobile equipment such as mobile
phones, PDAs, etc. Because it has a broad bandwidth,
it maintains satisfactory characteristics even when
its resonant frequency changes under the influenceof mounting environment. Thus it is believed that theantenna has many applications for 2.4~2.5 GHz wirelesscommunications equipment.
Using the same manufacturing process, development ofvarious antennas is under way including the main antennaof built-in type for CDMA (Code Division Multiple Access)equipment and multi-band antennas with dual- or tripleband. Based on these new products, we intend to develop
our product lineup.

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