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Progress In Electromagnetics Research, Vol. 107, 413–425, 2010
A COMPACT PLANAR HEXA-BAND INTERNAL
ANTENNA FOR MOBILE PHONE
J.-Y. Sze and Y.-F. Wu
Department of Electrical and Electronic Engineering
Chung Cheng Institute of Technology
National Defense University
190 Sanyuan 1st. St., Dasi Township
Taoyuan County 33508, Taiwan, R.O.C.
Abstract—A planar hexa-band internal antenna designed for mobile
phone applications is presented. The antenna occupying a small area
of 45 ×12 mm2is placed on the top no-ground portion of the system
circuit board with a ground-plane size of 45 ×100 mm2. The design
begins with constructing a meandered monopole. With a parasitic and
an impedance-adjustment structure subsequently added, the resulting
antenna can be viewed as a printed planar inverted-F antenna with
a parasitic resonant element. Two wide impedance bands can be
generated by the designed antenna to support GSM 850, GSM 900,
DCS, PCS, UMTS, and 2.4-GHz WLAN operations. The measurement
was found to agree reasonably well with the simulation. Design
procedures and rules along with the design concepts behind are all
presented in detail.
1. INTRODUCTION
In recent years, handheld mobile wireless communication devices
(especially mobile phones) have been widely and rapidly developed.
External appearances of these devices have been receiving increasingly
more attention. Besides keeping the appearances attractive, these
devices must be small not only in the plane parallel to the screen
but also in the thickness direction for becoming competitive in the
market. For attractiveness in appearance, internal antennas that
can be completely concealed in the case of a mobile phone are
now prevailing over external antennas [1–20]. However, the trend
Received 6 February 2010, Accepted 12 August 2010, Scheduled 27 August 2010
Corresponding author: J.-Y. Sze (jeffszejy@gmail.com).
414 Sze and Wu
for an upcoming mobile phone is that more components need to
be installed inside to make the mobile phone more powerful yet
possibly smaller in overall size. Hence, quite unfortunately, the
space in a mobile phone that can be allocated to deploy an internal
antenna becomes more and more limited. In addition, for better
functionality, most internal mobile-phone antennas are required to
provide operating bands wide enough to support the following five
communication standards: GSM 850 (824–894 MHz), GSM 900 (880–
960 MHz), DCS (1710–1880 MHz), PCS (1850–1990 MHz), and UMTS
(1920–2170 MHz). Communication networks involving these standards
are usually referred to as wireless wide-area networks (WWANs). In
order to access the internet, an additional band of 2.4–2.484 GHz for
WLAN applications is also desirable for the antenna mounted internal
to a mobile handset.
For ease of fabricating mobile handsets, printed internal antennas
have been designed to be integrated with ground planes and system
circuits on the same substrates [5–20]. Since the substrates employed
are usually very thin and the conductors printed on them are even
much thinner, it is safe to describe antennas of these types only
by their widths and heights, without emphasizing their thicknesses.
These antennas can be divided into four groups. Loop antennas in the
first group are operated as a half-wavelength resonant structure [5, 6].
Although being able to achieve penta-band operations for GSM 850,
GSM 900, DCS, PCS, and UMTS, antennas in this group suffer
from the drawback of having a large radiator area (as large as
900 mm2). In the second group, monopole antennas are operated as
a quarter-wavelength resonant structure [7–11]. When the radiator
in this type of antenna is close to the ground plane, the resulting
intensive coupling effect between the radiator and the ground plane
usually makes it difficult to design a quarter-wavelength monopole
antenna that not only preserves a small antenna height and width
but also achieves the desired hexa-band operations. In this group,
the antenna in [7] ([9]) although having a small antenna area of
38.5×15 = 577.5 mm2(60 ×10 = 600 mm2) can support only
the following five communication standards: GSM 900, DCS, PCS,
UMTS, and 2.4-GHz WLAN (GSM 850, GSM 900, DCS, PCS, and
UMTS). Belonging to the third group, monopole slot antennas can
also be operated as a quarter-wavelength resonant structure if the
slot is cut at the edge of the ground plane [12–15]. The monopole
slot antenna designed in [15] has a small size of 40 ×15 = 600 mm2
and can support the desired hexa-band operations. However, a height
of 15 mm may be regarded as too large for some mobile handsets.
In the fourth group are printed planar inverted-F antennas (printed
Progress In Electromagnetics Research, Vol. 107, 2010 415
PIFAs) [16–20], whose operations also rely on quarter-wavelength
resonance. A simple printed PIFA can be constructed by adding a
grounded strip to an inverted-L quarter-wavelength monopole [16, 17].
The height of a simple printed PIFA is usually smaller than those
of other types of antennas. However, a smaller height implies a
more intensive coupling effect between the radiator and the ground
plane, leading to a larger capacitive reactance and hence a poorer
impedance match. Although the impedance mismatch owing to the
intensive coupling effect can be improved by adding a grounded
strip that acts as an impedance-adjustment structure, the resulting
impedance bandwidth is often still not large enough. This is why
simple printed PIFAs [16, 17] are frequently adopted in the 2.4- and
5.2-GHz WLAN bands, for which the required fractional bandwidths
are only moderate, but not in other lower frequency bands for which
the required fractional bandwidths are relatively large. To overcome
this disadvantage, some research papers [18–20] have proposed printed
PIFAs using coupling feeding structures, instead of the direct feeding
ones employed in [16,17]. These antenna designs not only can support
WWAN or WWAN/WLAN operations but also have smaller antenna
heights (i.e., 11, 11, 10 mm for the antennas in [18–20], respectively)
than those in most of the antennas in [5–15]. Among them, the antenna
in [20], although having the smallest antenna height of 10 mm, can
support GSM 850/900/DCS/PCS/UMTS/2.4-GHz WLAN hexa-band
operations. However, the antenna width of 60 mm for the antennas
in [16, 18] may be considered large for some handsets.
In this paper, we aim to design for the desired hexa-band (WWAN
and WLAN) operations an internal printed direct-fed antenna that has
an width of 45 mm and that has an area of only 45 ×12 = 540 mm2,
which is smaller than those of all the mobile-phone antennas in [5–
15, 20] (note that the antennas in [16, 17] are for WLAN operations
only and those in [18, 19] are for laptop-computer applications). In
particular, the width (height) of 45 mm (12mm) is smaller than those of
the antennas in [5, 9, 18–20] ([5–8] and [13–15]). The designed antenna
is expected to provide two impedance bands, the lower (upper) of
which should cover the desired operating band of 824–960 MHz (1710–
2484 MHz) required by GSM 850 and GSM 900 (DCS, PCS, UMS, and
2.4-GHz WLAN). Although the designed antenna can be viewed as a
printed PIFA with a parasitic grounded inverted-L strip nearby, it was
actually constructed to be only a meandered monopole in the initial
design stage. With the excitation mechanism and impedance matching
of various resonant modes of the printed monopole presented step by
step, systematic design procedures and rules are developed to achieve
the goal.
416 Sze and Wu
2. ANTENNA CONFIGURATION
Figure 1 shows the geometry of the proposed planar internal antenna,
which is fabricated using a 0.8-mm-thick, 45-mm-wide, and 112-mm-
high FR4 substrate with dielectric constant 4.4. On the lower portion
of the FR4 substrate is a 45×100 mm2ground plane, above which is an
area of 45 ×12 mm2(referred to as the antenna area for convenience)
reserved to locate the designed antenna. The designed antenna,
according to its inherent functions, can be divided into three parts:
a main radiation structure (or called a main radiator), a parasitic
structure, and an impedance-adjustment structure (see the detailed
metal pattern in Fig. 1(b)); all these structures are printed coplanar
with the ground plane. The main radiator is a 1-mm-wide, 80-mm-long
metal strip that starts from the upper-right corner and is printed along
the E-D-C-B-A meandered path. This strip, which is to be excited at
point A and whose bottom edge is 1-mm away from the ground plane,
can be designed to resonate at about 960 and 2100 MHz. The parasitic
structure lies in the lower-right corner of the antenna area and is a 1-
mm-wide grounded inverted-L metal strip. This strip originates from
(a)
(b)
Figure 1. Compact planar hexa-band antenna for a mobile phone:
(a) perspective view of the entire structure, (b) metal pattern in the
antenna area.
Progress In Electromagnetics Research, Vol. 107, 2010 417
point F of the ground plane, extends upward along the right edge of the
substrate by a length of 9 mm, and then extends leftward by a length of
12 mm. The parasitic structure is implemented to excite one additional
resonant mode to widen the upper impedance band. The impedance-
adjustment structure is a 0.5-mm-wide inverted-L strip, whose 7-mm-
long horizontal section connects to point B of the main radiator and
whose 6-mm-long vertical section connects to point H of the ground
plane. This structure can improve the impedance matching in the
lower impedance band. Finally, the AB and BC sections of the main
radiator are widened to have a width of 3mm, resulting in a much
better impedance match in the upper resonant band. The design
procedures along with the design ideas behind are elucidated in the
next section.
3. CONCEPTS AND PROCEDURES OF ANTENNA
DESIGN
3.1. Preliminary Design of Main Radiator
For size reduction, many existing multi-band monopole antennas have
been constructed by bending a metal strip into meandered shape.
The meandered strip can be designed to resonate around multiple
pre-selected frequencies. The quarter-wavelengths of the first few
resonant modes are roughly the total length of the meandered strip
or the lengths of some particular sections bent in the meandered
strip. In this study, the main strip, whose route is E-D-C-B-A (see
Fig. 1(b)) with a total length of 80 mm, is also of meandered type. For
convenience, the antenna so constructed is a folded monopole antenna
referred to as the type 1 antenna. As shown in Fig. 2, the first three
Figure 2. Measured VSWR against frequency for the types 1, 2, and
3 antennas.
418 Sze and Wu
resonant modes of the folded monopole antenna are excited at around
960, 2100, and 3500 MHz. Simulated using Ansoft HFSS, the electric
current distributions of the resonant modes on the meandered strip
of the type 1 antenna are shown in Fig. 3. The quarter-wavelength
route of the electric current distribution at 960 MHz roughly has
the same length of the entire main radiator, whereas the A-B-C
quarter-wavelength route at 2100 MHz has a much shorter length of
about 35.7 mm. For the third resonant mode at 3500 MHz, the half-
wavelength route of the main electric current distributed between two
current nulls (depicted as circular dashed lines in Fig. 3(c)) has a
length of about 33 mm. Since the impedance band associated with the
third resonant mode is far beyond our frequency bands of interest, the
frequency response of that band will not be studied in the remaining
antenna design procedures.
3.2. Design of Parasitic Structure
Note that the upper (i.e., the second) VSWR ≤3 impedance band
of the type 1 antenna is far from wide enough to cover the desired
higher operating band (i.e., 1710–2484 MHz) for DCS, PCS, UMTS,
and 2.4-GHz WLAN operations. To achieve the goal, an additional
(a)
(b)
(c)
Figure 3. Resonant-mode elec-
tric current distributions on the
type 1 antenna at (a) 960 MHz,
and (b) 2100 MHz, (c) 3500 MHz.
(a)
(b)
(c)
Figure 4. Resonant-mode elec-
tric current distributions on the
type 2 antenna at (a) 850 MHz,
and (b) 1907 MHz, (c) 2560 MHz.
Progress In Electromagnetics Research, Vol. 107, 2010 419
resonant mode excited in the desired upper operating band is needed.
For that purpose, a grounded inverted-L strip functioning as a parasitic
structure is added in the lower-right corner of the antenna area to form
a type 2 antenna. Note that the right edge of the vertical section of the
parasitic structure is aligned with that of the substrate; the horizontal
section of the parasitic structure is set to be equal vertical distance
away from the two horizontal sections (i.e., the DE and BC sections)
of the main radiator.
With the length of the parasitic structure’s vertical section fixed
at 9 mm, the resonant mode excited in the parasitic structure can be
controlled by varying the length of the horizontal section. When the
length of the horizontal section is adjusted to 12 mm, the additional
resonant mode is excited at about 2500 MHz, whereas the first
and second resonant frequencies are slightly lowered from 960 and
2100 MHz of the type 1 antenna to 850 and 1907 MHz, respectively.
The changes in resonant frequencies can be explained by examining
on the type 2 antenna the electric current distributions depicted in
Fig. 4. Because of the presence of the parasitic structure, the open end
of the meandered strip around point E experiences a larger fringing
capacitance, resulting in a larger effective length of the meandered
strip than that of the type 1 antenna. Hence, although the current
distributions of the first two resonant modes on the meandered strips
of the types 1 and 2 antennas are very similar, the resonant frequencies
of the latter are slightly lower than those of the former. By contrast,
the quarter-wavelength current distribution of the additional (third)
resonant mode shown in Fig. 4(c) mainly concentrates on the parasitic
structure of the type 2 antenna, and the associated current distribution
on the meandered strip is much weaker and is quite different from
that of the third resonant mode of the type 1 antenna. The resonance
occurring mainly in the parasitic structure instead of the main radiator
explains why the third resonant frequency of the type 2 antenna
is farther away from that of the type 1 antenna than are the first
two resonant frequencies of the type 2 antenna away from those
of the type 1 antenna. Since the two resonant frequencies of the
second and third excited modes are close to each other, a wide upper
impedance band of 1800–2720 MHz is established. Unfortunately, the
parasitic structure has downgraded the impedance matching in the
lower resonant band, leading to a minimum VSWR of as high as 2.7
in that band.
3.3. Design of Impedance-adjustment Structure
For the type 2 antenna, the enhancement in the upper impedance
bandwidth accompanies an impedance mismatch in the lower resonant
420 Sze and Wu
Figure 5. Reflection-coefficient loci around the lower resonant bands
for the types 2 and 3 antennas.
band. To overcome this problem, we sought to adjust the input
impedance, especially in the lower resonant band. With a 0.5-mm-wide
grounded inverted-L strip connected to point B of the main radiator
to form a type 3 antenna, the first three resonant modes are excited
around the frequencies that are close to the resonant frequencies of
the type 2 antenna (the current distributions on the meandered strips
of these two antennas are very similar and are not shown here for
brevity). This grounded inverted-L strip provides adequate impedance
matching in the lower resonant band (see Fig. 2) and hence can be used
as the impedance-adjustment structure. The reflection-coefficient loci
of the types 2 and 3 antennas are shown in the Smith charts of Fig. 5.
This impedance-adjustment structure helps improve the impedance
matching in the lower resonant band around 850 MHz, leading to a
tightened resonant locus in the Smith chart for the type 3 antenna. The
resulting lowest VSWR is as low as 1.2, and the VSWR ≤3 impedance
band now ranges from 756 to 945 MHz, only slightly insufficient to cover
the desired lower operating band (i.e., 824–960 MHz) for GMS 850 and
GMS 900 operations.
3.4. Final Design of Main Radiator for Better Impedance
Matching
Although the impedance matching in the lower resonant band of the
type 3 antenna is greatly improved as compared with the type 2
antenna, the impedance matching around 2.2GHz in the upper
impedance band is downgraded. Obviously, the type 2 antenna’s upper
VSWR ≤3 impedance band has been split into the type 3 antenna’s
two disjoint bands, which are even more insufficient for completely
Progress In Electromagnetics Research, Vol. 107, 2010 421
enclosing the desired upper operating band of 1710–2484 MHz. To
overcome this problem, the strong variation of the electric current on
the main radiator needs to be smoothened. This can be accomplished
by widening the A-B-C section of the main radiator. The horizontal
BC section is widened toward the −zdirection, whereas the vertical
AB section is widened symmetrically toward the +yand −ydirections.
With the width (w1) of the A-B-C section changed from 1 to 3 mm, not
only can the upper VSWR ≤3 impedance band be enlarged to 1705–
2505 MHz, but a lower impedance band of 810–1010 MHz can also be
obtained, as shown in Fig. 6. Each of these two impedance bands can
completely cover its associated desired operating band. Hence, the
type 3 antenna with w1= 3 mm is selected to be our final designed
antenna. From Fig. 7, it is observed that the electric current on BC
section is smoothened after widening the width of the A-B-C section.
Figure 6. Measured VSWR for the type 3 antenna with different vales
of w1.
A
B
C
DE
F
G
H
D
CB
A
HF
E
G
(a)
(b)
A
B
C
DE
F
G
H
A
B
C
DE
F
G
H
D
CB
A
HF
E
G
D
CB
A
HF
E
G
(a)
(b)
(a)
(b)
Figure 7. Simulated electric current distributions of type 3 antenna
at 2200 MHz with different vales of w1: (a) w1= 1mm; (b) w1= 3 mm.
422 Sze and Wu
3.5. Radiation Characteristics of the Designed Antenna
Figure 8 shows for the final designed antenna the measured and
simulated far-field radiation patterns in the x-y,y-z, and x-zplanes
(a)
(b)
(c)
Figure 8. Measured and simulated far-field radiation patterns for
the three resonant modes of the designed antenna at (a) 920 MHz, (b)
1880 MHz, and (c) 2365 MHz.
Progress In Electromagnetics Research, Vol. 107, 2010 423
0.80 0.85 0.90 0.95 1.8 2.0 2.2 2.4 2.6
-6
-4
-2
0
2
4
6
8
10
0
20
40
60
80
100
Gain (measured)
Gain (simulated)
Radiation Efficiency (%)
Gain (dBi)
Frequency (GHz)
Radiation Efficiency (simulated)
Figure 9. Peak antenna gains and antenna efficiencies in the two
operating bands of the designed antenna.
at the frequencies of the three resonant modes. The measured and
simulated results agree reasonably well with each other. Shown in
Fig. 9 are the measured and simulated peak antenna gains and the
simulated antenna efficiency. The peak antenna gain in the lower
operating band is in the range of 0.6–2.2 dBi and that in the upper,
1.5–4.2 dBi; the efficiencies in the lower and upper operating bands
are around 60% and 70%, respectively, rendering the designed antenna
suitable for practical applications.
4. CONCLUSION
A planar hexa-band internal antenna proposed in this paper has been
successfully realized and discussed. The antenna was initially designed
as a meandered monopole and subsequently step-by-step developed
into a direct-fed printed PIFA with a parasitic resonant unit. The
structurally simple antenna not only occupies a small area of only
45 ×12 mm2but also has two VSWR ≤3 impedance bands of 810–
1010 MHz and 1705–2515 MHz, which can cover the desired operating
bands required for GSM 850, GSM 900, DCS, PCS, UMTS, and 2.4-
GHz WLAN operations. This antenna was measured to have good
radiation characteristics. The peak antenna gains in the lower and
upper operating bands are as high as 1.5 and 3 dBi, respectively,
making the antenna valuable for practical applications.
ACKNOWLEDGMENT
The authors would like to thank the reviewers for their careful review
and valuable suggestions. This work was supported by the National
424 Sze and Wu
Science Council of Taiwan, ROC, under Grand NSC 95-2623-7-014-
013-D. The authors are also grateful to the National Center for
High-Performance Computing, Taiwan, ROC, for computing time and
facilities.
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