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simulated and the measured data for reflection coefficient indi-
cates that a large bandwidth except only a slight frequency shift
in the resonance is achieved by this method. The slight discrep-
ancy between simulation and experiment may be caused by the
effect of an SMA connector and the soldering in addition to
errors in processing.
The far-field radiation patterns are measured in an anechoic
chamber with the Agilent-E8363B antenna-measurement system.
Figure 7 shows the measured normalized radiation patterns of
the optimized antenna at three frequencies: 4.55, 4.75, and 5
GHz. The antenna radiates at broadside radiation in both princi-
ple planes (E-plane and H-plane). The measured gain is plotted
in Figure 8, showing that the gain is about 6.2–6.7 dBi across
the operating band. It is worth noting that the antenna gain is
stable and the radiation patterns are similar in configuration over
the whole operating frequencies to that of the conventional
patch antenna.
5. CONCLUSIONS
The mixed model of BPSO and Zeland IE3D has been suc-
cessfully adopted to the automatic bandwidth broadening of a
patch antenna and a C-Band broadband patch antenna is suc-
cessfully designed. The antenna’s characteristics are calcu-
lated using the well-known Zeland IE3D software package,
whereas the bandwidth characteristic of the antenna is opti-
mized using BPSO technique. The comparison results show
that the 3.2% impedance bandwidth (4.63–4.78 GHz) of the
patch antenna is upgrade to 10.4% (4.47–4.96 GHz) through
the BPSO-IE3D method. The antenna gain is stable and the
radiation patterns are similar in configuration over the whole
operating frequencies to that of the conventional patch
antenna. The measured values of the antenna parameters are
found to match well with that of the simulated results, all of
which illustrate that the method is valid and the antenna can
operate well.
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VC 2011 Wiley Periodicals, Inc.
SMALL UWB ANTENNA WITH BANDSTOPFUNCTION FOR WIRELESS USB OFMOBILE HANDSETS
Yohan Lim, Young Joong Yoon, and Byungwoon JungDepartment of Electric and Electronic Engineering, YonseiUniversity, Seoul 120-749, Korea; Corresponding author:[email protected]
Received 28 April 2011
ABSTRACT: In this letter, a small and an internal ultra-wideband
(UWB) antenna for wireless USB of mobile handsets is proposed forUWB service in which bandstop function of 5.8-GHz wireless local areanetwork band is required. The ground is partially removed and the
microstrip feed line is gradually tapered to obtain enhanced impedancebandwidth. k/4 short slots for bandstop function are modified into L-type
to be accommodated in a small-sized antenna. From the measuredresults, wide bandwidth of 3.15–4.75 and 7.2–10.2 GHz is achievedwhile 5.8 GHz is notched. Three different shapes of conventional mobile
terminals are also considered for measurement. VC 2011 Wiley
Periodicals, Inc. Microwave Opt Technol Lett 54:438–441, 2012; View
this article online at wileyonlinelibrary.com. DOI 10.1002/mop.26551
Key words: UWB antenna; USB; band stop; mobile; handset
1. INTRODUCTION
Ultra-wideband (UWB) technique has been one of the most fas-
cinating technologies in indoor communications with various
antennas [1–3]. It has the merits of high speed transmission rate,
low power consumption, and simple hardware configuration
over conventional wireless communication systems. Recently,
there are attempt to include UWB system in USB dongles and
wireless USB for mobile handsets [4, 5]. To transmit and
receive UWB signals, UWB antennas are required in a mobile
terminal. However, previous UWB antennas for USB dongles or
wireless USB for mobile handsets have relatively large size or
high profile to be accommodated in mobile terminals. Moreover,
in the technology, the interference between UWB and wireless
local area network (WLAN) system has not considered [6, 7].
In this letter, we propose a small and an internal UWB
antenna for wireless USB of mobile handsets. It has very
438 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 54, No. 2, February 2012 DOI 10.1002/mop
compact size such that all radiators are is 10 mm � 7 mm � 1
mm and the antenna clearance is 14 mm � 16 mm, and it has
ultra wide bandwidth of 3.15–10.2 GHz with respect to VSWR
less than 2 and bandstop function of 5.8-GHz WLAN band. It is
also achieved that good radiation and gain performance in the
operating bandwidth. All simulations in this work were carried
out using CST Microwave Studio and a design example of the
proposed antenna is demonstrated.
2. ANTENNA STRUCTURE
The configuration of the proposed antenna is shown in Figure 1.
The antenna is fabricated on the FR4 substrate with dielectric
Figure 2 Return losses due to the gap between the radiator and the
ground plane, GW. [Color figure can be viewed in the online issue,
which is available at wileyonlinelibrary.com]
Figure 3 Return losses due to the gap between the radiator and the ground plane, AH. [Color figure can be viewed in the online issue, which is avail-
able at wileyonlinelibrary.com]
Figure 4 Current distribution of L-shaped short slots (a) 3.15 and (b)
5.8 GHz. [Color figure can be viewed in the online issue, which is avail-
able at wileyonlinelibrary.com]
Figure 1 Configuration of the proposed antenna
Figure 5 Return losses due to slot length, SL. [Color figure can
be viewed in the online issue, which is available at wileyonlinelibrary.
com]
DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 54, No. 2, February 2012 439
constant 4.5 and height of 1 mm and mounted on the top of the
printed circuit board (PCB) of handset.
The size of the PCB is 35 mm � 80 mm � 1 mm, and it is
a typical size for mobile handsets. The ground plane below the
radiator is partially removed for coupling between the radiator
and the ground plane, and it can also be enhanced impedance
matching. Moreover, the coupling effects make it helpful to
have small radiator. Tapered microstrip feed line is also used for
enhanced impedance matching over wideband. L-shaped short
slots are inserted in a radiator for bandstop function. Generally,
short sots are used to have antiresonance by inducing opposite
current at k/4of the required frequency. As the length of the slot
varies, the center frequency of the stop band can be changed.
Approximately, 7 mm of slot length is required for bandstop at
5.8 GHz but the radiator is too small to occupy slot length of 7
mm. Therefore, the shape of slot is modified to L-type and it
can be inserted in the radiator. The upper part of radiator (AH)
is folded to the backside of the PCB (�z direction) to extend
current path for covering low frequency of UWB. It has a merit
of low profile by using height of PCB.
3. SIMULATED RESULTS AND ANALYSIS
Based on the simulation by MWS, the proposed antenna is
designed and optimized to operate in all UWB band of 3.15–
10.2 GHz including bandstop function of 5.8-GHz WLAN.
According to the return loss characteristic of the proposed
antenna, most strongly influenced factor is the gap between the
radiator and the ground plane, GW, and those results are shown
in Figure 2. The length of 6 mm is determined after considering
characteristic of return loss and size of antenna clearance.
The variation of design parameters due to AH is shown in
Figure 3. It can be observed that the proposed antenna can
cover lower frequency as length of AH is longer. Length of 1
mm should be determined after considering not only character-
istic of return loss but also height of PCB because AH is
folded to the backside of the PCB (�z direction) to reduce its
profile by using height of PCB. Figure 4 shows the current dis-
tribution around L shaped short slots for bandstop function at
3.15 and 5.8 GHz. Even though length of the radiator AL is
smaller than length of 7 mm, which is required for bandstop at
5.8 GHz, the proposed antenna can have band stop function by
using L-shaped slots. Currents around the radiator and slots
have the same direction and currents are distributed to entire
ground plane at 3.15 GHz while opposite currents are strongly
generated at slots and most of currents cannot be delivered to
ground plane at 5.8 GHz.
The optimum design parameters of the proposed antenna are:
AW ¼ 10 mm, AL ¼ 7, AH ¼ 1, GW ¼ 6, FL ¼ 7, FL ¼ 15,
SL ¼ 4.75, and SW ¼ 2.5 mm. The total size for the antenna
clearance including feed line is 14 mm � 16 mm. It has very
compact size and low profile. Figure 5 shows return losses due
to slot length for variation of stop band. It can be seen from
Figure 5 that center frequency for band stop function can be
varied due to slots length and length of 4.75 mm is determined
for band stop at 5.8 GHz.
4. EXPERIMENTAL RESULTS
In Figure 6, the fabricated antenna is compared with previous
UWB antenna [8]. It can be seen that the proposed antenna have
very compact size compared with the previous UWB antenna.
The proposed antenna is directly fed by coaxial cable and the
antenna is located in top left of PCB.
The proposed antenna was housed with three kinds of
handset terminals of bar, slide, and folder type for measure-
ment and those return losses are shown in Figure 7 compared
with return loss of bare type. It shows that the impedance
bandwidth with voltage standing wave ratio (VSWR) less
than 2 is from 3.15 to 10.4 GHz. It covers all UWB band
and rejects the band at 5.8 GHz. As shown in Figure 8, the
radiation patterns were measured at 3.15, 5.8, and 7.2 GHz
and XZ-plane patterns are omni-directional. Table 1 shows the
measured maximum gain of the proposed antenna. The gain
varies from 1.27 to 2.79 dBi on the azimuth plane except the
stop band and proposed antenna can have the maximum gain
from �2.28 to 0.11 under the condition that the antenna was
housed with the cases of mobile terminals.
Figure 6 Photo of the proposed antenna (a) front and (b) back. [Color
figure can be viewed in the online issue, which is available at
wileyonlinelibrary.com]
Figure 7 Measured return loss of the proposed antenna for the various
mobile terminals. [Color figure can be viewed in the online issue, which
is available at wileyonlinelibrary.com]
TABLE 1 Maximum Gain of the Proposed Antenna for theVarious Mobile Terminals
Model
4.0 GHz
(MHz)
Maximum
Gain (dBi)
5.8 GHz (MHz)
7.2 GHz
(MHz)
Bare 5.85 �17.34 1.27
Bar type �1.01 �17.42 �2.28
Slide type 0.09 �16.24 �0.35
Folder type �0.92 �16.15 �1.41
440 MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 54, No. 2, February 2012 DOI 10.1002/mop
5. CONCLUSIONS
We proposed a small UWB antenna for mobile handsets to
operate for UWB band including bandstop function. It can
have wide impedance matching due to the partially removed
ground plane and tapered feed line and cover all UWB band
of 3.15–10.2 GHz. It can have bandstop function of 5.8-GHz
WLAN by using slots of L-type. Moreover, it has very com-
pact size. After all, it will have very strong potential for next
generation of convergence between UWB system and mobile
handsets.
ACKNOWLEDGMENTS
This research was supported by the LG Electronics, Seoul,
Korea.
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VC 2011 Wiley Periodicals, Inc.
Figure 8 Measured radiation pattern of the proposed antenna for the various mobile terminals (a) bare (b) bar type (c) slide type, and (d) folder type.
[Color figure can be viewed in the online issue, which is available at wileyonlinelibrary.com]
DOI 10.1002/mop MICROWAVE AND OPTICAL TECHNOLOGY LETTERS / Vol. 54, No. 2, February 2012 441
