998 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 9, 2010

Folded Dual-Loop Antennafor GSM/DCS/PCS/UMTS

Mobile Handset ApplicationsChia-Hao Ku, Hsien-Wen Liu, Student Member, IEEE, and Sheng-Yu Lin

Abstract—A folded dual-loop antenna suitable for GSM/DCS/PCS/UMTS applications is proposed. It is fabricated using a pair ofsymmetric meander strips to form two loops. By properly bendingthe radiating strips, the antenna can achieve a compact size of50 ( ) 9 ( ) 9 ( ) mm� to be integrated within a mobilehandset device as an internal antenna. With 6 dB return loss, twooperating frequency bands covering 847–971 and 1670–2230 MHzcan be obtained with our design. Moreover, the resonant charac-teristics of the antenna can be tuned by using various strip lengthsand also spaces between the radiator and the ground plane. Ex-perimental results exhibit that the proposed folded dual-loop an-tenna features nearly good omnidirectional radiation patterns withproper gain, so it is well suitable to meet GSM/DCS/PCS/UMTSoperations for mobile handset applications.

Index Terms—Digital Cellular System (DCS), Folded dual-loopantenna, Global System for Mobile Communications (GSM), Per-sonal Communication System (PCS), Universal Mobile Telecom-munication System (UMTS).

I. INTRODUCTION

W ITH the rapid growth of communication technologies,several important wireless systems including Global

System for Mobile Communications (GSM: 890–960 MHz),Digital Cellular System (DCS: 1710–1880 MHz), Per-sonal Communication System (PCS: 1850–1990 MHz),and Universal Mobile Telecommunication System (UMTS:1920–2170 MHz) to be integrated within a mobile handsetdevice has been a new trend. To this end, antenna design withsome desirable features such as multiband operation, lightweight, low profile, and easy fabrication have earned high at-tention for practical applications. Thus, many studies to satisfymultiband operation have been proposed in [1]–[7]. A built-infolded monopole antenna using meander lines for handset ap-plication was reported in [1]. To reduce antenna size, a numberof folded loop antennas using a tuning stub [2] or bent-shapedstructure [3]–[5] to implement multiband operation were also

Manuscript received August 21, 2010; revised September 25, 2010; acceptedOctober 05, 2010. Date of publication October 21, 2010; date of current versionNovember 04, 2010.

C.-H. Ku is with the Department of Electrical Engineering, Ming Chi Univer-sity of Technology, Taipei 24301, Taiwan (e-mail: kuchiahao@mail.mcut.edu.tw).

H.-W. Liu and S.-Y. Lin are with the Department of Electrical Engineering,National Taiwan University of Science and Technology, Taipei 106, Taiwan(e-mail: D9407303@mail.ntust.edu.tw; M9707602@mail.ntust.edu.tw).

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.2010.2089037

investigated for integration into a handset device as an internalantenna. Furthermore, hybrid designs, consisting of loop andmonopole antennas to operate at GSM/DCS/PCS/UMTS sys-tems, were widely discussed in [6] and [7]. However, all thesedesigns cannot be easily embedded inside a handset device dueto their large sizes.

In this letter, we propose a compact folded dual-loop antennato meet GSM/DCS/PCS/UMTS operations for mobile handsetapplications. This antenna, formed with a bent-shaped radiator,consists of a pair of symmetric meander strips, which only occu-pies a small size of 50 ( ) 9 ( ) 9 ( ) mm . By properlydesigning the strip length as well as space between the radiatorand the ground plane, the antenna can realize not only good res-onance property, but also two desired operating frequency bandscovering 847–971 and 1670–2230 MHz. Owing to such tunablefeatures, the frequency shifting from the device casing can bebetter solved when the antenna works inside a mobile handset.Compared to previous studies presented in [1]–[7], the proposedantenna with a more compact size and a tunable loop structure isthus satisfactory to achieve GSM/DCS/PCS/UMTS operationsfor integration within a mobile handset as an internal antenna.Details of the design concept of the antenna are described inSection II, and a fabricated prototype of the proposed antennais constructed and experimentally studied in Section III. Para-metric study for the antenna will be performed and discussed aswell. Finally, this letter will be concluded with a brief summaryin Section IV.

II. ANTENNA DESIGN

Fig. 1(a) depicts the whole geometry of the proposed foldeddual-loop antenna, which utilizes a pair of symmetric meanderstrips to form two loops for achieving GSM/DCS/PCS/UMTSoperations. These strips are all designed with a union widthof 1 mm and implemented using a 0.2-mm-thick copperplate.To reduce the antenna size, the proposed design is constructedwith two perpendicular layers to obtain a bent-shaped ra-diator. The overall dimensions of the antenna are merely50 ( ) 9 ( ) 9 ( ) mm to be embedded inside a mobilehandset. In this letter, a 0.2-mm-thick copperplate with a size of90 ( ) 50 ( ) mm is selected as the ground plane for sim-ulating general handset application. Note that a shielding planevertical and connecting to the ground plane can be employedto support the casing of a mobile handset. Since the proposeddesign works with a balanced structure, a balun to be connectedbetween the antenna and the feeding cable will be accordinglyutilized for measurements.

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KU et al.: FOLDED DUAL-LOOP ANTENNA FOR GSM/DCS/PCS/UMTS MOBILE HANDSET APPLICATIONS 999

Fig. 1. Geometry of the proposed folded dual-loop antenna. (a) Whole struc-ture. (b) Detailed design parameters. (� � ���� mm, � � � mm, � �

� mm, � � � mm, � � � mm, and � � ��� mm).

To meet the multiband demands of GSM/DCS/PCS/UMTSsystems, multiple resonance paths are required in our antennadesign. Hence, two loops of the antenna need to be developedwith different lengths, as shown in Fig. 1(b). We can observethat the longer loop of about path A–C–D–E–F–G–H–I–B,corresponding to one wavelength at 900 MHz, is working forthe lower band. With regard to the upper band operation, theshorter loop of about path A–C–D–F–H–I–B is designed to beone wavelength at 1800 MHz. For widening the upper band,the center vertical strips having a coupling structure also cangenerate a resonant mode at 2100 MHz, where a gap amongthem is well evaluated about 1 mm to realize good radiationperformance. Consequently, two proper operating frequencybands suitable for GSM/DCS/PCS/UMTS applications canbe achieved with our antenna design. Also note that a gapbetween the feeding point A and the grounding point B isdesigned to be 8 mm, which is capable of tuning the operatingfrequencies of the antenna. An electromagnetic (EM) softwarepackage, Ansoft HFSS, has been used to simulate and analyzethe electrical characteristics and radiation performance of theproposed antenna. The design parameters optimized for theantenna have been eventually determined with mm,

mm, mm, mm, mm, andmm. A photograph of the implemented prototype of

the proposed antenna is shown in Fig. 2.

III. RESULTS AND DISCUSSIONS

A fabricated prototype for the proposed folded dual-loop an-tenna was constructed and tested. A vector network analyzer(Agilent 8362B) was used to measure and examine the antenna

Fig. 2. Photograph of the proposed folded dual-loop antenna.

Fig. 3. Simulated and measured return losses of the proposed antenna.

performance. It should be noted that a balun to be connected be-tween the antenna and the feeding cable was properly exploitedfor those measurements. Fig. 3 illustrates the simulated and ex-perimental return losses against the frequency of the antenna,where fairly good agreements between them can be attained.As seen, two measured impedance bandwidths with 6 dB returnloss for the proposed antenna have been determined to be about847–971 and 1670–2230 MHz, corresponding to 13.6% and28.7%, respectively. Hence, the proposed antenna design withmultiband property is capable of satisfying the requirements ofGSM/DCS/PCS/UMTS systems for practical applications.

On the other hand, a parametric study to analyze the antennaperformance has been performed by utilizing the solver HFSS.Simulated return losses of the proposed antenna with variousgaps are compared and indicated in Fig. 4. Obviously, loweroperating frequency can be obtained by using a narrower gap,whereas higher operating frequency needs a wider gap. This isbecause the narrower gap works with a longer loop path and thewider gap is with a shorter one. Besides, the space betweenthe antenna and the ground plane can be also used to tune theoperating frequency, as shown in Fig. 5. We can find that whenthe space is reduced, the antenna radiates with a lower oper-ating frequency due to the capacitive coupling. By utilizing a

1000 IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 9, 2010

Fig. 4. Simulated return losses versus various gaps � for the proposed antenna.

Fig. 5. Simulated return losses versus various spaces h between the antennaand the ground plane.

Fig. 6. Simulated return losses for the antenna with and without the couplingstrip.

large space, a higher operating frequency can be achieved aswell. Properties for the antenna with and without the center ver-tical strips around the point F are also simulated in Fig. 6. It isclear that the antenna using these strips can reach a lower op-erating frequency and a wider bandwidth. This is because the

Fig. 7. Measured radiation patterns of the proposed antenna. (a) 900 MHz.(b) 1800 MHz. (c) 2100 MHz.

center vertical strips around the point F work as not only a cou-pling structure, but also a pair of shorting strips. Therefore, an

KU et al.: FOLDED DUAL-LOOP ANTENNA FOR GSM/DCS/PCS/UMTS MOBILE HANDSET APPLICATIONS 1001

Fig. 8. Measured peak antenna and radiation efficiency of the proposed an-tenna. (a) Lower band. (b) Upper band.

effect in regard to the frequency shifting caused by the casingof a mobile handset device may be well addressed with suchadjustable property. This also means that the proposed foldeddual-loop antenna is well suitable to be integrated within a mo-bile handset as an internal antenna for GSM/DCS/PCS/UMTSapplications.

To examine the radiation performance of the antenna, a 3-Dspherical near-field antenna measurement system produced byNSI has been utilized. Fig. 7 exhibits the measured far-fieldradiation patterns in the , and planes for the fre-quencies at 900, 1800, and 2100 MHz, respectively. As seen,nearly good omnidirectional patterns have been obtained in the

plane over these three frequencies. This further implies thatfairly good coverage for GSM/DCS/PCS/UMTS operations

can thus be attained with our design. In addition, the measuredpeak gains and radiation efficiencies versus the frequency ofthe proposed antenna are plotted in Fig. 8. For operating inthe lower band, as shown in Fig. 8(a), the peak gain variesfrom 1.28 to 1.62 dBi, and the radiation efficiency is largerthan 64.2%. Results to demonstrate the antenna performance atthe upper band are given in the Fig. 8(b), where the peak gainvaries within 2.16–2.65 dBi, and the efficiency is also betterthan 75.3%. Accordingly, reasonably stable variation for bothgain and efficiency can be received with our antenna design,so better communication quality for GSM/DCS/PCS/UMTSsystems can be realized as well.

IV. CONCLUSION

A compact folded dual-loop antenna to be integrated within amobile handset for GSM/DCS/PCS/UMTS operations has beenproposed and investigated in this letter. This antenna utilizes notonly two loops to implement multiband operation, but also abent-shaped radiator to well reduce the whole size. Comparedto prior studies, the proposed design can easily tune the oper-ating frequencies to solve the effect from the casing of a handsetdevice. Furthermore, some properties such as good omnidirec-tional coverage and stable gain variation can be satisfactorilyachieved across the operating frequency bands for the antenna.For these reasons, the proposed antenna design with a compactsize is well suitable for integration into various mobile handsetsto meet GSM/DCS/PCS/UMTS applications.

REFERENCES

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