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IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 11, 2012 403

Ultrawideband Antenna for LTE/GSM/UMTSWireless USB Dongle Applications

Yong-Ling Ban, Jin-Hua Chen, Li-Jun Ying, Joshua Le-Wei Li , Fellow, IEEE , and Yu-Jiang Wu

Abstract— In the letter, a simply printed planar antenna cov-ering GSM850/900/1800/1900/UMTS2100 and LTE700/2300/2500operating frequency bands for wireless USB dongle applicationsis proposed, designed, and fabricated. The presented antenna con-

sists of a large patch and a matching network in order to enhanceimpedance bandwidth. The upper operating bands includingGSM1800/1900/UMTS2100/LTE2300/2500 are primarily at-tributed to the large patch. Meanwhile, the lower resonant modescovering LTE700/GSM850/900 bands are generated physically by

ground planes of both the USB dongle circuit board and the laptopboard. The impedance matching over all bands is improved by thematching network. The proposed antenna occupies a small size of

mm and can be easily printed on a 0.8-mm-thick FR4

substrate of conventional dimensions of mm , whichmakes it promising for wireless USB dongle applications.

Index Terms— Antennas, printed antennas, ultrawideband an-

tennas, USB dongle.

I. I NTRODUCTION

W ITH rapid development of wireless communication

technology such as WLAN and GSM/UMTS/LTE

WWAN systems, laptops and other digital devices with wire-

less network access functions [1]–[11] are becoming very

popular. A wireless USB dongle, a small terminal that can beconnected to a computer, has been developed as a wireless

adapter designed to compensate for the insuf ficient bands

of laptops and other digital devices. However, realizing in-

ternal multiband antenna design in such a small USB dongle

with a common size of mm is considerably chal-

lenging. In recent years, extensive research activities have

been dedicated toward the development of multiband antennas

for wireless USB dongle applications [1]–[9], monopole

antennas [1]–[6], meander-line antennas [7], and planar in-

verted-F antennas [8], [9]. Most of these designs generally

require complicated two- or three-dimensional structures. As

a result, it leads to, on one hand, a large size in the radiator inwireless USB dongle devices. On the other hand, some of these

complicated antennas [1]–[9] cannot cover a bandwidth broad

Manuscript received February 06, 2012; revised March 05, 2012; acceptedMarch 15, 2012. Date of publication April 06, 2012; date of current versionApril 23, 2012. This work was supported in part by the National Science Foun-dationof China under ProjectNo. 61171046and HuaweiTechnologies Co., Ltd.

The authors are with the Institute of Electromagnetics and School of Elec-tronic Engineering, University of Electronic Science and Technology of China,Chengdu 611731, China (e-mail: [email protected]; [email protected];[email protected]; [email protected]; [email protected]; [email protected]).

Color versions of one or more of the figures in this letter are available onlineat http://ieeexplore.ieee.org.

Digital Object Identifier 10.1109/LAWP.2012.2192470

enough for future communication requirements, especially for

GSM850/900/1800/1900/UMTS2100 and LTE700/2300/2500

band. Due to dif ficulties of achieving ultrawideband operations

under stringent volume limits, there lacks new progress, and

much work needs to be further done.

With the above-mentioned issues in mind, a novel sur-

face-mount printed antenna for wireless USB dongle appli-

cations is proposed. Compared to most of the existing USB

dongle antennas reported in [2] and [4]–[6], the presently pro-

posed antenna has very simple physical structure and relatively

wider operating bandwidths covering GSM850/900/1800/1900/

UMTS2100 (824–894 MHz/880–960 MHz/1710–1880 MHz/

1850–1990 MHz/1920–2170 MHz) and LTE700/2300/2500

(698–806 MHz/2305–2400 MHz/2500–2690 MHz). Design

considerations of the presented antenna are described in the

following sections, where simulated and measured results for

the fabricated prototype are both depicted and discussed.

II. A NTENNA PROPOSED FOR USB DONGLE

Fig. 1(a) shows the physical geometry of the proposed an-

tenna for wireless USB dongle applications, where dimensions

of the metal pattern of the proposed antenna are detailed in

Fig. 1(b). In the design, the main antenna component locatednext to the USB interface has a small dimension of mm

and is mounted on an inexpensive 0.8-mm-thick FR4 substrate

of relative permittivity 4.4 (which serves as the USB dongle’s

circuit board). Notice that the stated USB dongle ground plane

does not cover the entire part of the substrate, leaving a non-

ground area on the other side of the antenna pattern. Then, the

USB dongle circuit board with an area of mm is con-

nected to the big laptop ground plane (through the USB interface

with a size of mm for transmitting wireless data). The

laptop display ground and the keyboard ground form an angle

of 90 (as a common professional standard), both with the same

dimension of mm . In the configuration, the USB

dongle ground is printed on the other side in the antenna de-

sign, and R F signal can be transmitted to the antenna via a 50-

microstr ip feed line.

The proposed antenna comprises two major portions, that is,

a big rectangular patch and a matching network. The network is

constructed in terms of a lumped chip capacitance and a lumped

chip inductance. Therefore, some electromagnetic energy can be

coupled into the USB dongle ground plane and the major laptop

ground plane via the gap between the big radiating patch and the

USB dongle ground. Moreover, the end of the chip inductance is

connected to the USB dongle ground via a metallic hole in order

to enhance the performance of the impedance matched over the

wide bandwidth of interests. As shown in Fig. 1, both length

1536-1225/$31.00 © 2012 IEEE

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404 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 11, 2012

Fig. 1. (a) Geometry of the proposed antenna for wireless USB dongle appli-cations. (b) Detailed dimensions of the antenna (whose units are in millimeters).

and width of the radiating patch are 18 mm (which is about

0.25 wavelength at 3200 MHz), and they produce a resonant

mode at 3200 MHz. The fundamental resonant mode at about

800 MHz is excited by the gaps between the large patch and

the USB dongle ground and the laptop ground. By adjusting

the value of the chip inductance and the gap width , two wide

operating frequency bands 698–960 and 1710–2690 MHz can

be obtained ultimately.

In the experiment, the antenna is fed by a 50- microstrip

line connected to an SMA connector for testing the con-

structed prototype of the proposed antenna. Since the design

needs to cover two wide bandwidths, LTE700/GSM850/900

and DCS1800/PCS1900/UMTS2100/LTE2300/2500, and a

USB dongle of low-profile characteristics should be easily

Fig. 2. (a) Photograph of the fabricated USB dongle and laptop computer (overall view). (b) Enlarged photograph of the fabricated USB dongle (topicalview).

Fig. 3. Measured and simulated return loss of the proposed antenna.

embedded, a big foreground is considered for mobile digital

receivers, and at the same time a good performance of the

antenna should be maintained. Fig. 2 depicts the proposed

antenna printed on the FR4 substrate.

III. R ESULTS AND DISCUSSIONS

The proposed antenna was then fabricated and tested. Fig. 3

shows the measured and simulated return losses of the proto-

type. The simulated results are obtained using Ansoft HFSS and

are in agreement with the measured data. Obviously, a broad

operating bandwidth of about 2315 MHz (ranging from 685 to

3000 MHz) with return loss better than 6 dB (i.e., 3:1 VSWR)

is obtained. As a universal criterion, the 3:1 VSWR definition is

generally adopted for the internal mobile terminal device an-

tenna for WWAN operations and serves as a commonly ac-

cepted industrial standard.To analyze the excitation mechanism in the studies, we

attempt to figure out how the antenna performance is affected

by adjusting the chip capacitance and inductance of matching

network in Figs. 4 and 5. The simulated input impedance on

the Smith chart for the frequency ranges of 650–1000 and

1700–2700 MHz are shown. In the design considerations

depicted in Fig. 4 and subsequently in other figures, all di-

mensions are the same as those given in Fig. 1 if they are not

specified. As plotted in Fig. 4, varying the chip capacitance

indeed significantly affects impedance-matching bandwidth in

the lower bands. With decreasing the chip capacitance, poor

matching bandwidth will be seen in LTE700/GSM850/900

bands, while the upper operating bands will be improved.

Obviously, compared to the other chip capacitance, nearly the

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BAN et al.: ULTRAWIDEBAND ANTENNA FOR LTE/GSM/UMTS WIRELESS USB DONGLE APPLICATIONS 405

Fig. 4. Simulated input impedance on the Smith chart for the proposed antennaas a function of the chip capacitance .

Fig. 5. Simulated Smith chart for the proposed antenna as a function of thechip inductance .

entire desired loop of the impedance curve for the proposed

design is shifted inside the 3:1 VSWR circle.

Similar results can be observed in Fig. 5. By increasing the

chip inductance , it is helpful for the lower bandwidth cov-

erage, however the desired upper input impedance matching is

poor when equals 15.0 nH. For different designed parameters,

the input impedance (Im curves and Re curves) of the proposed

design nH is smaller than that of the other chip in-

ductance. Naturally with the impedance matching enhancement

for the desired frequencies over the antenna’s lower band from

698–960 MHz, good excitation of a wide operating band for the

Fig. 6. Simulated return loss as a function of the proposed design with or without laptop.

Fig. 7. Simulated return loss as a function of the gap’s width between the bigradiating patch and the USB dongle ground plane.

proposed antenna’s upper band from 1710–2690 MHz can still

be achieved (most of the impedance curves fall within the 3:1

VSWR circle).

When compared to the reference antenna without the laptop,

as shown in Fig. 6, the results clearly indicate that no reso-

nant mode is excited at about 750 MHz. This behavior confirms

the lower band is significantly affected by the laptop ground

plane, meaning that the laptop is a significant portion of the pro-

posed antenna. The proposed antenna is an entire effective radi-

ating structure formed by: 1) the radiating elements; 2) the USB

dongle ground plane; and 3) the laptop ground plane. The whole

antenna confi

guration constitutes an effective radiating system.Furthermore, the role of the coupling gap is discussed in

Fig. 7. Results of the simulated return loss for varied from 0.5

to 1.5 mm (other dimensions have no variations) show that there

are large effects on the impedance matching of the antenna’s

lower band and small variations in the impedance matching of

the upper band. This behavior confirms that the lower band is

significantly affected by the coupling gap, meaning that good

impedance matching of the lower band can be effectively ad-

justed by the gap .

The measured and simulated radiation patterns at 830 and

2170 MHz are plotted in Fig. 8. At 830 MHz, the measured

radiation patterns in all the three planes are nearly omni-

directional, as shown in Fig. 8(a). At 2170 MHz, relatively

complicated radiation patterns over the antenna upper band

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406 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 11, 2012

Fig. 8. Measured radiationpatternsof theproposedantenna at twofrequencies:(a) 830 MHz and (b) 2200 MHz.

Fig. 9. Measured antenna gain andradiation ef ficiency of the proposed antennaversus frequency. (a) Lower band for LTE700/GSM850/900. (b) Upper band for

GSM1800/1900/UMTS2100/LTE2300/2500.

are obtained and shown in Fig. 8(b). However, there are a

few differences between measured and simulated patterns at

830 and 2170 MHz, and the measured results of the proposed

antenna are less than the simulated results. In fact, this is

owing to that the practical coaxial cable used in measure-

ments leads to radiation variations of the whole structure

and also to power loss in experiments, whereas the cable is

not assumed in simulations. Fig. 9 shows the measured and

simulated antenna gain and measured radiation ef ficiency of

the proposed design. In Fig. 9(a), results for the lower band are

presented. Small variations of the antenna gain (for measured

and simulated results) in the range of about 1.3–2.6 dBi are

seen for LTE700/GSM850/900 operation, and the measured

radiation ef ficiency varies from about 55% to 64%. For the

upper band shown in Fig. 9(b), the measured antenna gain

for DCS1800/PCS1900/UMTS2100/LTE2300/2500 operation

varies from about 2.3 to 5.6 dBi, and the simulated antenna gain

for the upper band is 3.8–6.2 dBi, while the measured radiation

ef ficiency ranges from about 56% to 70%. Obviously, the above

results of the obtained radiation characteristics indicate that the

presented antenna is a good solution for practical wireless USB

dongle (attached to laptop) applications.

IV. CONCLUSION

A novel printed antenna for wireless USB dongle applica-

tions has been designed, presented, and discussed in this letter.

Made of a big radiating patch and a matching network, the an-

tenna can cover LTE700/2300/2500, GSM850/900/1800/1900,

and UMTS2100 frequency bands entirely, while the occupied printed size of the proposed antenna on the circuit board is only

400 mm in size. Compared to the existing common scheme

available elsewhere, the presently proposed USB dongle an-

tenna has a simple structure but a very good radiation perfor-

mance. Finally, the return loss, radiation ef ficiency, and antenna

gain are acceptable. Because the antenna is easily fabricated

on the printed circuit board (PCB) (using the printed circuit

boards), it is very promising for mobile applications.

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