Furukawa ElectricNewNew Products
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Small and Low-Profile Multiband Antennas for Mobile Phones

INTRODUCTION

Many improvements are being made in mobile phoneequipment to respond to user requirements for multifunctionality, multiband capability to support 3rd generation communication protocols, thinner handsets, and soon. Increasingly antennas are being built in, so that user
requirements in terms of communication performancemust be met under the stringent conditions inside thehandset.
To respond to these requirements, we describe hereantennas that we have marketed that incorporate proprietary structures and materials, are thin (only 2.5 mm) andsmall, and have multiband capability.

2.

FEATURES

2.1 General description
To achieve antennas that are smaller and thinner, yetdeliver the required characteristics, we have introduced
technologies of basic circuit patterning, materials andstructure that differ from those of existing products. Figure
1 shows typical antennas designed to suit various handset configurations. These antennas comprise a 3-layer
dielectric, with radiation elements connected to bothsides of the dielectric that constitutes the middle layer.
The features of these antennas are summarized as follows.
2.2 Parallel 2-Wire Circuitry
The increasing trend to handsets with multiband capability has resulted in a need for antennas that cover an
extremely broad range of frequencies. However sinceantennas are built-in they are smaller and connected toground, making it more difficult to cover an expandedband. Accordingly we have modified the radiation element with respect to a planar inverted-F antenna (PIFA),
thereby reducing the size, and, by disposing in parallel a
conductor of substantially the same configuration as theradiation element, have expanded the bandwidth.
Simulation data demonstrating this effect are shown inFigure 2.
2.3 High Dielectric Loading
By loading a material with a high dielectric constant as
the radiation element of the antenna, it is possible toreduce antenna size. However our proprietary conductor
structure as described above (a conductor of substantiallythe same configuration aligned in parallel) presents two
problems: 1) if a material of high dielectric constant isloaded between conductors, the bandwidth becomes
extremely narrow; and 2) normally materials that have ahigh dielectric constant also have a high dielectric loss
tangent, with a consequent tendency for radiation resistance to decrease.
For this reason we have developed a resin for injection
molding which can be applied as a coating to the outsideof the conductor only, and which also has a high dielectric
constant (approximately 18) while the rise in dielectricloss tangent is held to about 0.002 (the “new material”
referred to in Figure 3). By means of this material it hasPIFA

Antenna with expanded bandwidth8720
GND5VSWR1.

654323Dimensions in mm

11.4 1.45 1.5 1.55 1.6 1.65 1.7 1.75 1.8 1.85 1.9

Frequency（GHz）

Figure 1

Typical antennas.

Figure 2

Example of bandwidth expansion.

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Small and Low-Profile Multiband Antennas for Mobile Phones

been possible to achieve both reduced size and expanded bandwidth.
2.4 Manufacturing Process
To realize the features described above, we have developed a manufacturing process, similar to that for PCBs, inwhich a middle layer material (low-dielectric material) isfabricated with double-sided interconnect patterning, andis inserted into an injection-molding die for molding, sothat the high-dielectric material is coated onto the outside. Further, with this structure and manufacturing process we have achieved antennas of 2.5-mm thickness.
A variety of mounting configurations are in demand forthe built-in antennas, depending on the individual handset. As an example, Figure 4 shows a mounting configuration using a PCB that supports coaxial cable power
supply. The antenna is disposed in the narrow space
under the battery. A wide variety of other mounting configurations are also possible in accordance with handset
requirements, such as power supply by spring and direct
soldering of power supply terminal to the PCB.

Phenol resin

Dielectric loss tangent

LCP
Acrylic resin
Epoxy resin
Polycarbonate
Polyimide resin
Polyphenylene sulfide

CHARACTERISTICS

Since antenna characteristics are affected by the configuration of the ground connection used, characteristics
were evaluated by standard boards (GND) simulating
mobile phone size. The frequency characteristics ofVSWR are shown in Figure 5 and those for antenna radiation efficiency in Figure 6. In the standard GSM bandwidth(880~960 MHz), VSWR was substantially below 3 andradiation efficiency was substantially above 40 %, and at
DCS/PMS/UMTS (1710~2170 MHz), VSWR was below 4
and radiation efficiency was above 40 %, achieving
extended bandwidth and high efficiency.

4.

CONCLUSIONAs described above, we believe that these small and thinmultiband-capable antennas based on our proprietary
structure and materials can contribute to securing communications performance for various types of handsets.
We also believe that mobile phones will become evensmaller and have even greater functionality, and weremain committed to pushing further with the development of materials and to optimizing antenna design tosecure antenna performance, even in this environment.
For more information, please contact:
Antenna Solution Team, Electronics Components Dept.,
Electronics and Automotive Systems Co., Furukawa
Electric
TEL: +81-3-3286-3295 FAX: +81-3-3286-3960

0.10000.01003.

High dielectric constant LCP

Thermosetting
PPO resin + glass
樹脂＋ガラスNew material
BT resin
Alumina substrate

0.0010Polyphenylene ether
Polyethylene

3458121620

Dielectric constant（E）
Thermoplastic resins

Figure 3

Thermosetting resins

VSWR

2New material developed here

Dielectric constant vs. dielectric loss tangent for
selected resins.

9977

VSWRPTFE
0.0001533

10.80 0.84 0.88 0.92 0.96 1.00 1.04

11.50 1.58 1.66 1.74 1.82 1.90 1.98 2.06 2.14 2.22 2.30

Frequency (GHz)

Frequency (GHz)

Figure 5

Front caseBattery area

GND connection and ﬁxed terminal
Connection to main substrate

Example of antenna mounting.

80

Radiation eﬃciency (%)

Coaxialcable

Figure 4VSWR characteristics.

Antenna
Radiation eﬃciency (%)

Connection to coaxial cable

5644832
161008060402000.80 0.84 0.88 0.92 0.96 1.00 1.04

01.50 1.58 1.66 1.74 1.82 1.90 1.98 2.06 2.14 2.22 2.30

Frequency (GHz)

Frequency (GHz)

Figure 6

Antenna radiation efficiency characteristics.

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