Multi-band hybrid antenna for ultra-thinmobile phone applications

H. Rhyu, J. Byun, F.J. Harackiewicz, M.-J. Park, K. Jung,D. Kim, N. Kim, T. Kim and B. Lee

A compact hybrid antenna consisting of two PIFAs and a slot antennais proposed for ultra-thin mobile phone applications. The antenna has avery compact volume of 46 � 10 � 4.2 mm3, and it operates at GSM850/900, DCS, PCS, and UMTS bands, simultaneously. Results showthat its bandwidth and efficiency are sufficient for these penta-bandmobile phone applications.

Introduction: To bring convenient worldwide roaming services tomobile communication systems, antennas for mobile phones shouldsupport multi-band operation including GSM 850/900 (824–894/880–960 MHz), DCS (1710–1880 MHz), PCS (1850–1990 MHz),and UMTS (1920–2170 MHz) bands. As ultra-thin mobile phoneswith antenna heights of typically 4 to 6 mm become the current trendof mobile phone applications, the role of antenna miniaturisationbecomes key in achieving multi-band mobile phones. For multi-bandoperations such as GSM 850/900, DCS, PCS, and UMTS bands, themost important issue is how to obtain a wide bandwidth (136 MHz)for GSM 850/900 at the lower frequency bands and how to design acompact antenna size without severe degradation of antenna perform-ance. A few antenna designs utilise the resonant modes of a chassis aspart of the antenna for wideband operations [1, 2]. However, these tech-niques have fewer degrees of freedom in designing various shapes ofpractical mobile phones. In addition, it is not easily tuned to cover thewhole GSM 850/900 band since the resonances at the lower frequencybands are usually determined by the size of the PCB ground plane usedfor practical mobile phones. There are other design techniques in con-junction with hybrid antenna structures combining resonance modesfrom different types of radiating elements such as slots, monopoleslots, and monopole T-strips [3, 4]. While these antennas are very effec-tive in achieving a wide bandwidth especially at the lower frequencybands of GSM 850/900, their sizes are still somewhat too large tomeet recent demands in the miniaturisation process of mobilephones. The antenna in [3] occupies a large surface area of 945 mm2

(25 � 45 mm2), and the antenna in [4] has a volume of over3450 mm3 (8 � 8 � 54 mm3).

In this Letter, a hybrid antenna structure consisting of two PIFAs andan open slot antenna is proposed to cover GSM 850/900, DCS, PCS,and UMTS bands. This proposed antenna has a very compact volumeof less than 1940 mm3 which is a reasonable volume in the currentantenna trend of ultra-thin mobile phone applications.

Design and results: Fig. 1 shows the geometry of the proposed antenna,and Fig. 2 shows the photograph of the fabricated antenna. The size ofthe ground plane is 46 � 85 � 1 mm3, and the size of the antennaelement is 46 � 10 � 4.2 mm3. There are three metallic layers, layers1, 2 and 3. There is 1 mm thickness of the FR4 (1r ¼ 4.4) substratebetween layers 1 and 2, and there is 3.2 mm thickness of the FR4 sub-strate between layers 2 and 3. Layers 2 and 3 are electrically connectedby the strips at the connecting points as shown in Fig. 1a. The proposedantenna consists of two PIFAs and one open-ended slot antenna. OnePIFA (PIFA 1) has a quarter-wavelength at GSM 850, which startsfrom the shorted point on layer 2 to the open ‘A’ point on layer 3,and another PIFA (PIFA 2) has a resonant length from the shortedpoint on layer 2 to the open ‘B’ point on layer 3. An open-ended slotantenna is printed on layer 2, and its resonant slot has a quarter-wave-length at GSM 900. These three antenna elements are fed using ahybrid feed (slot-coupled feed and capacitively coupled feed) printedon layer 1. The impedance matching for two PIFAs depends mainlyon the thickness of an FR4 substrate between layers 1 and 2 and thelength of a feed line. The impedance of an open-ended slot antenna ismatched by adjusting the offset of the feed line from the end of theslot. By an open-ended slot antenna in conjunction with PIFA 1, awide bandwidth covering the GSM 850/900 band can be achieved.Combining the fundamental mode of PIFA 2 and the higher mode ofPIFA 1, the frequency bandwidth for DCS, PCS, and UMTS bands isalso obtained. Fig. 3 shows the simulated and measured results ofreturn loss. The VSWR is less than 3 for all operating bands. Theeffect of a feed cable is minimised by attaching the measurement

ELECTRONICS LETTERS 16th July 2009 Vol. 45

cable to the lower electric field region and locating the feed point ofan inner conductor of a feed cable close to the ground plane.However, one can still see some disagreement between simulation andmeasurement results in Fig. 3 because of the disturbance of a feedcable. The bandwidth (VSWR , 3) is 16.8% (818–968 MHz)especially at the lower frequency bands, GSM 850/900, and this isachieved by generating each fundamental mode of a hybrid antenna insuch a small volume. Fig. 4 shows that the proposed antenna has agood efficiency over 40% in all operating frequency bands.

unit: mm 6

3.2 17

10 open ‘A’

open ‘B’ 19

3 FR4 FR4

shorted connecting point

ground plane

open slot

a

b

2

2 2

8 3 1

1 4

19 15.5 7

shorted

ground plane

feed point

ground plane layer 1

feed line

1.5 1.5

22

21 3

3

1

1

1.5

2.5

layer 2

connecting points

layer 1

1.5 1.5

z

y

xφ

θ

2

layer 3 layer 2

Fig. 1 Geometry of proposed antenna

a Overall structureb Dimensions in detail for layers 1 and 2

a

b

Fig. 2 Photograph of fabricated antenna

a Top viewb Rear view

No. 15

0

–5

–10

–15

–200.5 1.0 1.5

frequency, GHz

2.0 2.5

retu

rn lo

ss, d

B

GSM 850GSM 900

DCS 1800

VSWR 3:1

PCS 1900UMTS

Fig. 3 Return losses

——— measured. . .. . .. . .simulated

80

70

60

50

40

30

20 800 820 840 860 880 900

a

b

920 940 960 980

ante

nna

effic

ienc

y, %

80

70

60

50

40

30

20

1650 1700 1750 1800 1850 1900

frequency, MHz

frequency, MHz

1950 2000 2100 2150 2200

ante

nna

effic

ienc

y, %

Fig. 4 Antenna efficiency

a GSM 850/900 bandsb DCS/PCS/UMTS bands

ELECTRO

Conclusion: A novel compact antenna is proposed for multi-bandmobile phones which has a very low profile. The proposed antenna uti-lises a hybrid structure with the conjunction of two PIFAs and an openslot antenna, so that it has sufficient bandwidth and efficiency for alloperating frequency bands including GSM 850/900, DCS, PCS, andUMTS bands.

# The Institution of Engineering and Technology 200930 May 2009doi: 10.1049/el.2009.1530

H. Rhyu, M.-J. Park, K. Jung, D. Kim, N. Kim and B. Lee (Departmentof Wireless Communications Engineering, Kwangwoon University, 447-1, Wolgye-Dong, Nowon-Gu, Seoul, 139-701, Korea)

E-mail: bj_lee@kw.ac.kr

J. Byun (Telecommunication R&D Center, Samsung Electronics Co.Ltd, 416, Maetan-3dong, Yeongtong-Gu, Suwon-Si, Kyeonggi-Do433-742, Korea)

F.J. Harackiewicz (Department of Electrical and ComputerEngineering, Southern Illinois University Carbondale, Carbondale,IL 62901, USA)

T. Kim (Division of General Education–Mathematics, KwangwoonUniversity, 447-1, Wolgye-Dong, Nowon-Gu, Seoul, 139-701, Korea)

References

1 Antonino-Daviu, E., Suarez-Fajardo, C.A., Cabedo-Fabres, M., andFerrando-Bataller, M.: ‘Wideband antenna for mobile terminals basedon the handset PCB resonance’, Microw. Opt. Technol. Lett., 2006, 48,pp. 1408–1411

2 Lindberg, P., Ojefors, E., and Rydberg, A.: ‘Wideband slot antenna forlow-profile hand-held terminal applications’. Proc. 36th IEEE EuropeanMicrowave Conf., Manchester, UK, September 2006, pp. 1698–1701

3 Wu, C.H., and Wong, K.L.: ‘Hexa-band internal printed slot antenna formobile phone application’, Microw. Opt. Technol. Lett., 2008, 50,pp. 35–38

4 Lin, C.I., and Wong, K.L.: ‘Internal hybrid antenna for multibandoperation in the mobile phone’, Microw. Opt. Technol. Lett., 2008, 50,pp. 38–42

NICS LETTERS 16th July 2009 Vol. 45 No. 15