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:yjyoon@yonsei.ac.kr

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