A Broadband Interior Antenna of Planar Monopole Type in Handsets

IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 4, 2005 9
A Broadband Interior Antenna of Planar Monopole
Type in Handsets
Yong-Sun Shin, Seong-Ook Park, and Manjai Lee, Member, IEEE
Abstract—A novel internal antenna of planar monopole type
is presented for broadband applications. The proposed antenna
fed by a 50- microstrip line covers the digital cordless system
(DCS, 1710–1880 MHz), personal communication system (PCS,
1750–1870 MHz), and international mobile telecommunication
(IMT-2000, 1885–2200 MHz) bands within S 11 10 dB. The
antenna occupies a compact volume of 20 17 4.7 mm 3 and
it is suitable to be built-in within the housing of a mobile phone.
The bandwidth of the proposed antenna (VSWR 2) has
740 MHz starting from 1620 to 2360 MHz. The IE3D software and
microwave studio (MWS) simulation are employed for optimizing
the design parameters, and the simulation results are in agreement
with those of the measured one, considering each associated case
of the antenna itself, phone case, and battery.
Index Terms—Broadband, interior antenna, mobile antenna,
planar monopole.
I. INTRODUCTION
WITH the rapid growth of mobile communications there is
several growing demands with handset design requirements
for small, lightweight, multifunction, and multiband. At
the same time, the mobile handset adapts popularly the internal
antenna structure also. Therefore, these demands for wireless
terminal are an explosive issue.
The planar monopole antenna is a good candidate for wireless
communication because of its simple structure, omni-directional
radiation characteristic, low profile, and lightweight
internal antenna [1]. In the previous researches, the impedance
bandwidth of the planar monopole antenna has been increased
by several techniques such as modifying geometries of bow-tie
and trapezoidal shapes [2], [3], adding a parasitic element [4],
and thickening the radiator. In addition, it is important to consider
the mobile phone case and battery because resonant frequency
and impedance bandwidth are changed by the effect of
them [5].
This paper presents a novel internal antenna of the planar
monopole type for application in mobile phones. The bandwidth
is improved by applying the trapezoidal feeding shape and
tilting it [2], [6]. The proposed antenna size has a small volume
of 20 17 4.7 mm which includes the supporter and it can
achieve a broad bandwidth of about 740 MHz capable of operating
the digital cordless system (DCS, 1710–1880 MHz), personal
communication system (PCS, 1750–1870 MHz), and
Fig. 1. Geometries of the proposed antenna. (a) The side and top views. (b)
Detail dimensions and trapezoidal feed shape.
international mobile telecommunication (IMT-2000,
1885–2200 MHz) bands. In order to check the effect of the
case and battery of the mobile phone, the antenna is placed
on the practical handsets of a folder type with the size of
46.16 92.24 21.64 mm . Each associated impedance
bandwidth is obtained about 680 MHz starting from 1590 to
2270 MHz with case, and 450 MHz starting from 1570 to 2020
MHz with case and battery.
Details of the antenna designs, the simulated and experimental
results of the impedance bandwidth, and radiation
characteristics are investigated.
Manuscript received July 20, 2004; revised November 19, 2004. This work
was supported by the National Research Laboratory, Ministry of Science and
Technology, Korea, under Contract M1-0203-00-0015.
The authors are with the School of Engineering, Information and Communications
University, Daejeon 305-714, Korea (e-mail: shinturtle@icu.ac.kr;
sopark@icu.ac.kr; manjai@icu.ac.kr).
Digital Object Identifier 10.1109/LAWP.2004.841623
II. ANTENNA CONFIGURATION
The geometries of the proposed antenna are shown in Fig. 1.
The size of the main substrate is 40 75 1mm which is
considered as the circuit board of a practical handset. As seen
in Fig. 1(a), the antenna is fed by a 50- microstrip feed line
1536-1225/$20.00 © 2005 IEEE

10 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 4, 2005
Fig. 5.
Measured return losses considering hand phone case and battery.
Fig. 2. The case and battery of the practical mobile phone [model: SPH-X8300
anycall intenna (Samsung)].
Fig. 3.
Measured and simulated return losses of only antenna.
Fig. 4.
Simulated current distribution at 1800 MHz.
Fig. 6. Measured and simulated results of the return losses. (a) Return losses
with case. (b) Return losses with case and battery.
which consists of a metal strip width of 1.68 mm. In order to
achieve the broad bandwidth, the feed which is connected between
the microstrip line and antenna is a trapezoidal shape with
a tilted angle of 34.7 in Fig. 1(b). By adjusting the width of
the bottom and top side of a trapezoidal feed, the
broad bandwidth can be achieved [2] due to the tilting copper

SHIN et al.: BROADBAND INTERIOR ANTENNA OF PLANAR MONOPOLE TYPE IN HANDSETS 11
Fig. 7.
Measured and simulated radiation patterns of the proposed antenna at 1800 MHz. (a) x-z plane (1800 MHz). (b) x-y plane (1800 MHz).
Fig. 8.
Measured and simulated radiation patterns considering phone case. (a) x-z plane (1800 MHz). (b) x-y plane (1800 MHz).
plate. Also, the resonant frequency can be shifted lower because
the traveling current path is longer. As a result, the broad
bandwidth can be achieved. The antenna is placed on a supporter
with a height of 4.5 mm which has relative permittivity
. As seen in Fig. 1(b), the basis of the proposed antenna
is a planar monopole type of three pieces of copper strip
with the dimensions of 20 17 0.2 mm which occupies a
small volume in handsets. Fig. 2 shows the fabricated antenna
mounted on the practical mobile phone with the dimensions of
46.16 92.24 21.64 mm . The antenna is designed in the real
operating environment with the handset case and battery. Because
the presence of the handset case and battery can alter the
resonant frequency and radiation patterns, this paper includes
their effects for antenna analysis. In order to find the optimized
antenna characteristics, microwave studio (MWS) is used to
tune each associated parameter of antenna structure. Fabrication
and measured results were compared with the simulated ones.
III. RESULTS
The designed antenna has fabricated and measured with an
Agilent 8510C network analyzer to confirm its performance.
Fig. 3 shows the measured and simulated results of the antenna
without considering the case and battery which resonates at
1810 MHz with the bandwidth 41.1% at . In order
to check the current flows at the resonance frequency, the simulation
result in Fig. 4 is obtained from the IE3D software.
There are two current paths in Fig. 4 corresponding to the upper
branch and lower branch at the resonance frequency of 1800
MHz. These total lengths of the current paths are about 41.5 mm

12 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 4, 2005
Fig. 9.
Measured and simulated radiation patterns considering phone case and battery. (a) x-z plane (1800 MHz). (b) x-y plane (1800 MHz).
IV. CONCLUSION
TABLE I
THE SIMULATED AVERAGE GAINS IN THREE PRINCIPAL PLANES
and 44.2 mm, which are corresponding to an approximately
quarter-wavelength at 1700 and 1800 MHz, respectively.
Fig. 5 shows the measured return losses considering the antenna
itself, phone case, and battery. Fig. 6 shows the measured
and simulated return losses in cases considering the hand
phone case and battery. As shown in Fig. 6, the resonated frequency
is shifted by the presence of case and battery. Each associated
bandwidth has 680 MHz (1590–2270 MHz) with case
and 450 MHz (1570–2020 MHz) with case and battery. The simulation
results are performed with MWS. The experimental results
have a good agreement with the simulated results. Fig. 7
shows the measured and simulated radiation patterns of the antenna
itself at the frequency of 1800 MHz. It is seen that the
radiation patterns are approximately omnidirectional and similar
to those of a z-directed electric monopole. Table I shows the
simulated average gains in three principal planes. The measured
maximum gain has 2.3 dBi, while the simulated maximum gain
has 2.54 dBi at 1800 MHz.
Figs. 8 and 9 show the radiation patterns of the antenna with
the placement of case and battery, respectively. The measured
maximum gain is about 2.8 dBi with case and 3.1 dBi with case
and battery, while the simulated maximum gain has 2.98 and
3.2 dBi at 1800 MHz, respectively. This slight discrepancy can
be attributed to the effects of the conductor loss and dielectric
loss of case, battery, and other conductors in the mobile phone.
The characteristics of the broad bandwidth and omnidirectional
radiation patterns are very suitable for handset application.
A novel internal antenna of planar monopole type suitable
for DCS, PCS, and IMT-2000 bands has been proposed and investigated.
In addition, the antenna is applied to the practical
handsets. The proposed antenna has a compact dimension of
20 17 4.7 mm and when it is considered case and battery in
practical handsets, further reduction size of the antenna is possible.
Also, if the slot which has the taped shape of edges is
added in the center from the feed part with a trapezoidal shape
to each branch of prototype antenna, the global system for mobile
(880–960 MHz) band can be achieved.
The obtained bandwidth is 740 MHz at
and the
measured maximum gain is 2.3 dBi without considering the battery
and handset case. Each associated bandwidth is 680 MHz
(1590–2270 MHz) with case and 450 MHz (1570–2020 MHz)
with case and battery at
and the maximum gains
are 2.8 and 3.1 dBi, respectively. The omnidirectional radiation
patterns are similar to those of the monopole antenna. These features
make the proposed antenna attractive for mobile handsets.
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