A Novel Hexa-Band Antenna for Mobile Handsets Application

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dBi at the resonance frequency. Antenna 3 provides a maximum gain of 2.2 dBi at 1.52 GHz for the CP state.

IV. CONCLUSION

A single feed electronically reconfigurable microstrip antenna with switchable slots for frequency and polarization diversities has been presented in this communication. The antenna can produce linear and circular polarization by controlling the bias conditions of two PIN diodes. A good impedance matching performance for all polarization states is observed without any matching networks. The proposed design achieves a cross polar level better than010 dB in linear po-larization and 1.18% CP bandwidth in circular popo-larization state with broadside radiation characteristics and moderate gain. In addition, the antenna is simple and compact because it uses only a few active and passive components and requires less area to occupy the patch and dc-bias circuit compared to conventional polarization diversity antennas. The frequency and polarization diversities of this design provide some potential applications for wireless communications.

REFERENCES

[1] J. Mitola and G. Q. Maguire, “Cognitive radio: Making software ra-dios more personal,” IEEE Personal Commun. Mag., vol. 6, no. 4, pp. 13–18, Aug. 1999.

[2] M. A. Kossel, R. Kung, H. Benedickter, and W. Bachtold, “An active tagging system using circular polarization modulation,” IEEE Trans. Microw. Theory Tech., vol. 47, no. 12, pp. 2242–2248, Dec. 1999. [3] M. Boti, L. Dussopt, and J.-M. Laheurte, “Circularly polarized antenna

with switchable polarization sense,” Electron. Lett., vol. 36, no. 18, pp. 1518–1519, Aug. 2000.

[4] F. Yang and Y. Rahmat-Samii, “A reconfigurable patch antenna using switchable slots for circular polarization diversity,” IEEE Microw. Wireless Compon. Lett., vol. 12, no. 3, pp. 96–98, Mar. 2002. [5] M.-H. Ho, M.-T. Wu, C.-I. G. Hsu, and J.-Y. Sze, “An RHCP/LHCP

switchable slotline-fed slot ring antenna,” Microw. Opt. Technol. Lett., vol. 46, no. 1, pp. 30–33, Jul. 2005.

[6] M. K. Fries, M. Grani, and R. Vahldieck, “A reconfigurable slot antenna with switchable polarization,” IEEE Microw. Wireless Compon. Lett., vol. 13, no. 11, pp. 490–492, Nov. 2003.

[7] Y. J. Sung, “Reconfigurable patch antenna for polarization diversity,” IEEE Trans. Antennas Propag., vol. 56, no. 9, pp. 3053–3054, Sep. 2008.

[8] B. Kim, B. Pan, S. Nikolaou, Y.-S. Kim, J. Papapolymerou, and M. M. Tentzeris, “A novel single-feed circular microstrip antenna with recon-figurable polarization capability,” IEEE Trans. Antennas Propag., vol. 56, no. 3, pp. 630–638, Mar. 2008.

[9] M. Ali, A. T. M. Sayem, and V. K. Kunda, “A reconfigurable stacked microstrip patch antenna for satellite and terrestrial links,” IEEE Trans. Antennas Propag., vol. 56, no. 2, pp. 426–435, Mar. 2007.

[10] S. V. Shynu, G. Augustin, C. K. Aanandan, P. Mohanan, and K. Va-sudevan, “A compact electronically reconfigurable dual frequency mi-crostrip antenna for L-band applications,” Int. J. Wireless Opt. Comm., vol. 2, no. 2, pp. 181–187, 2004.

[11] M. S. Nishamol, V. P. Sarin, A. Gijo, V. Deepu, C. K. Aanandan, P. Mohanan, and K. Vasudevan, “Compact dual frequency dual polarized cross patch antenna with an x-slot,” Microw. Opt. Technol. Lett., to be published.

A Novel Hexa-Band Antenna for Mobile Handsets Application

Chia-Mei Peng, I-Fong Chen, and Chia-Te Chien

Abstract—A novel hexa-band antenna for mobile handsets application is proposed and analyzed in this communication. An asymmetric T-type monopole antenna with a shorted-line is designed to be operated in code-division multiple access (CDMA, 824–894 MHz), global system for mo-bile communications (GSM, 880–960 MHz), digital communication system (DCS, 1710–1880 MHz), personal communication system (PCS, 1850–1990 MHz), wideband code division multiple access (WCDMA, 1920–2170 MHz) and Bluetooth (2400–2484 MHz) bands. A prototype of the proposed an-tenna with 50 mm in length, 3 mm in height and 15 mm in width is fab-ricated and experimentally investigated. The experimental results indicate that the VSWR 2.5:1 bandwidths achieved were 17.8% and 37.1% at 900 MHz and 2100 MHz, respectively. The specific absorption rate (SAR) for an input power of 24 dBm in CDMA, GSM and WCDMA bands, and an input power of 21 dBm in DCS and PCS bands all meet the SAR limit of 1.6 mW/g. Experimental results are shown to verify the validity of theoretical work.

Index Terms—Hexa-band antenna, mobile handsets, shorted-line, spe-cific absorption rate (SAR), T-type monopole.

I. INTRODUCTION

Wireless communications continue to enjoy exponential growth in the cellular telephony, wireless Internet, and wireless home networking arenas. In order to roam worldwide, the operation bands of major wireless services, such as code-division multiple access (CDMA), global system for mobile communications (GSM), digital commu-nication system (DCS), personal commucommu-nication system (PCS), wideband code division multiple access (WCDMA) and Bluetooth should be simultaneously considered [1]. Downsizing the handset unit, which has seen remarkable progress in recent years, requires the size reduction of the antenna element also. However, as a small antenna element is used, the utilization of the handset body is beneficial to enhance antenna performance of the handset because the handset body is usually larger than the antenna element. Therefore, the overall ef-fective antenna dimensions augment dramatically. As a consequence, the corresponding gain and the bandwidth of the antenna system are increased [2]–[10]. While the use of the handset body as a part of the radiator is advantageous, it also caused disadvantage at the same time in practical operation. The antenna performance in terms of gain and input impedance varies due to the influence of the human head and hand. In this communication, an asymmetric T-type monopole antenna is designed jointly with a solid shorting-line to achieve hexa-band

Manuscript received September 16, 2010; revised November 13, 2010; ac-cepted January 26, 2011. Date of publication July 07, 2011; date of current ver-sion September 02, 2011. This work was supported by the National Science Council, R.O.C., under Contract 97-2221-E-228-004.

C.-M. Peng and I.-F. Chen are with the Department of Electronic Engineering and Institute of Computer and Communication Engineering, Jinwen University of Science and Technology, Taipei, Taiwan, R.O.C. (e-mail: ex0206@just.edu. tw). .

C.-T. Chien us with the Department of Electronic Engineering and Institute of Computer and Communication Engineering, Jinwen University of Science and Technology, Taipei, Taiwan, R.O.C. and also with the Department of Communi-cation Engineering, National Chiao Tung University, Hsinchu, Taiwan, R.O.C. Color versions of one or more of the figures in this communication are avail-able online at http://ieeexplore.ieee.org.

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3428 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 59, NO. 9, SEPTEMBER 2011

Fig. 1. (a) Geometry of the proposed antenna for hexa-band operation in the mobile handset. (b) Dimensions of the proposed antenna.

(CDMA, GSM, DCS, PCS, WCDMA and Bluetooth) performance. A hexa-band antenna is constructed to operate in the range of a dual operating-band: lower-operating band (CDMA and GSM) and upper-operating band (DCS, PCS, WCDMA and Bluetooth). The proposed antenna has a dual asymmetric radiated-strip structure that is developed by modifying the structure of a printed T-type monopole. The feasibility of wide bandwidth operation has been proven by the design of a solid shorted-line and a solid open-stub radiating structure to operate in the dual operating bands. Smaller power loss (dB absorp-tion) due to the influence of phantom-head model is shown. It is also demonstrated that the proposed antenna structure produces a low spe-cific absorption rate (SAR) value. Details of the design considerations and the experimental results of the constructed prototype are presented and discussed in the following sections.

II. ANTENNASTRUCTURE ANDDESIGN

Fig. 1(a) shows the geometry of the proposed antenna for hexa-band operation in the mobile handset. The presented antenna structure is composed of an asymmetric T-type monopole which is printed on a FR4 glass epoxy substrate with the thickness of 1.6 mm, relative permittivity of 4.3 and loss tangent of 0.023. The proposed antenna is placed on a portion without metal ground on the backside. All sections are at the same layer. One of the asymmetric T-type strips combined with solid shorting-line to form a loop structure is denoted as part A. The other strip combined with solid open-stub is denoted as part B. The electrical-length of the radiating elements can be determined from the quarter-wave length at the resonant frequencies. Detailed dimensions of the proposed antenna are given in Fig. 1(b). In part A, the resonant frequency is designed to occur at 1800 MHz, the electrical-length of the planar-strip is equal to 40 mm (which is 15 mm + 25 mm). For covering DSC, PCS,

WCDMA and Bluetooth bands, the shape of part A is designed for wideband operation, the tuning of broad bandwidth is obtained by increasing strip-area and inserting some slits. These slits cause the discontinuities of the current distribution on the surface of radiating-strip which improves the impedance bandwidth [11], [12]. In part B, the resonant frequency is designed to occur at 900 MHz, the electrical-length of the planar-strip is equal to 80 mm (which is 15 mm + 25 mm + 6 mm + 22 mm + 5 mm + 7 mm). For covering CDMA and GSM bands, the solid-open stub is used as a top-loading of part B and it increases the electrical-length and impedance bandwidth in the antenna’s lower-operating band. The impedance matching at lower- and upper-operating bands can be also tuned by solid shorting-line of part A and extended strip of part B. The solid shorting-shorting-line is found to be effective in obtaining a wider impedance bandwidth in the antenna’s upper-operating band. Note that the widths of these strips, slits, solid shorting-line and solid open-stub, etc., are not identical. By selecting appropriate dimensions (part A, part B) of the antenna struc-ture, good impedance matching of the asymmetric T-type monopole can be obtained, and thus the bandwidth is also extended. Besides, [7] indicated that the ground-plane mode is responsible for SAR. Hence, in order to demonstrate the low current distribution on the handset body, the effect of varying the ground-plane length of the proposed antenna structure is investigated by simulations. Detail results will be presented and discussed in the next section.

III. EXPERIMENTALRESULTS ANDDISCUSSION

In the experiment, the feeding-point and ground-plane are connected to a 50 SMA connector. By using the described design procedure, a hexa-band antenna is constructed to operate in the range of a dual oper-ating-band: lower-operating band (CDMA and GSM) and upper-oper-ating band (DCS, PCS, WCDMA and Bluetooth). Fig. 2(a) shows the measured and simulated V.S.W.R plot of the dual band antenna and the V.S.W.R 2 bandwidths are 135 MHz (15%) and 790 MHz (37.6%) at 900 MHz and 2100 MHz, respectively. The simulated results are ob-tained by using the Ansoft HFSS. We can also find that a good agree-ment between the simulation and measureagree-ment is obtained. Fig. 2(b) shows the measured V.S.W.R of the proposed antenna in terms of part A and part B. For part A only, the radiated-strip and the shorting-line is matched at the DCS, PCS and WCDMA bands, the 560 MHz (28% at 2000 MHz) operating bandwidth is shown. This is due to the fact that the surface current distribution of the asymmetric radiated-strip is dis-continuous. For part B only, the modified bended monopole antenna is matched at the GSM and PCS bands. As expected, the measured results indicate that part A and part B introduce an upper- and lower-operating band, respectively.

The measured Smith Chart as shown in Fig. 2(c), the full charac-teristics of the proposed antenna are shown. Fig. 3 presents the mea-sured 3-D and 2-D radiation patterns in the free space at 850 MHz and 902 MHz in the xy-plane and yz-plane, respectively. It is obvious that the dipole-like radiation patterns are observed. In other words, at the lower-operating bands, the ground-plane becomes a part of the antenna, and is responsible for the radiation [7]. The measured radiation patterns at 1720, 1920, 2045 and 2450 MHz are shown in Fig. 4. From Fig. 4, more variations in the radiation pattern-shapes are obtained, as com-pared to those in Fig. 3. This is probably because the ground-plane still acts as a part of the antenna at the upper-operating band. The overall ground-plane length is about one wavelength long and there are nor-mally four main lobes at the upper-operating band.

Table I. presents the measured antenna total efficiency of the pro-posed antenna in the free space (without head and phantom-hand), and with phantom-head and phantom-hand.

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Fig. 2. (a) The measured and simulated V.S.W.R against frequency. (b) The measured V.S.W.R in terms of the part A and part B. (c) The measured Smith Chart of the proposed antenna.

Acceptable radiation characteristic for the practical applications is obtained for the proposed antenna. The omni-directional feature of the proposed antenna can be observed from the Horizontal-plane. The ef-fect of the proposed antenna structure on the antenna performance is also studied and the results are described below. In addition, the SAR results of the proposed antenna are also analyzed.

Fig. 3. Measured 3-D and 2-D radiation patterns at (a) 850 MHz and (b) 902 MHz for the proposed antenna.

A. Analysis of the Proposed Antenna Structure

The design parameters and the corresponding characteristics of the resonant frequency, input impedance and bandwidth are a function of the geometrical parameters of the proposed antenna. The simulated cur-rent distribution of the proposed antenna structure on the handset body is shown in Fig. 5. In the upper-operating band, only a few current is distributed on the handset body. Note that a small loop antenna can be regarded as a magnetic dipole normal to the loop plane and it re-duces the current flow on the handset body [6], [7]. However, in the lower-operating band, more current are distributed on the handset body as compared to those in the upper-operating band. That is because in the lower-operating band, the electrical-length of the modified bended monopole is over one quarter-wavelength, as a consequently, the input impedance of the modified bended monopole is matched to the handset body [3]–[7]. When a mobile handset is used in close proximity to a human head, dielectric-loading effect can be expected, there may also be a detuning issue. In order to demonstrate the distinctive performance of the proposed antenna in the presence of a human head, the measure-ment efficiency set-up with the phantom-head is shown in Fig. 6. The liquid parameters used in the measurements are listed in Table II. The measured V.S.W.R against frequency of antenna with phantom-head is shown in Fig. 7.

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The degradation of total efficiency of antenna with phantom-head is shown in Table I.

TABLE I

THEMEASUREDANTENNAGAINS AND THETOTALEFFICIENCYWITHIN THE

OPERATINGBANDWIDTH OF THEPROPOSEDANTENNA

Fig. 5. The simulated current distribution of the proposed antenna structure on the handset body (the ground-length is 100 mm) at (a) 850 MHz, (b) 902 MHz, (c) 1720 MHz, (d) 1920 MHz, (e) 2045 MHz, (f) 2450 MHz.

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Fig. 6. Photo of experimental arrangement for efficiency measurement with (a) Phantom-head. (b) Phantom-hand.

Fig. 7. Measured V.S.W.R against frequency of antenna with phantom-head and hand.

B. Analysis of the SAR

The SAR in passive mode has been measured using Dasy-4 system [13], as shown in Fig. 8. The antenna is placed at the cheek position of the right-hand side of the phantom, and the spacing between the ground-plane and the cheek is 3 mm. Two cases for the proposed tenna test are shown in Fig. 9. The input power of the proposed an-tenna at GSM, CDMA and WCDMA bands is 24 dBm. However, the

TABLE II

THELIQUIDPROPERTY OFPHANTOM-HEAD/HAND

Fig. 8. Photo of experimental arrangement for SAR measurement.

Fig. 9. The physical model for measuring SAR with the proposed antenna at the top and bottom position of the handset body.

input power at DCS and PCS bands is 21 dBm (both considering a user channel being 1/8 of a time slot) [2]. The liquid parameters used in the measurements are listed in Table III. The measured SAR results in 1 g mass of simulated tissue from exposure to the antenna radiation are listed in Table IV. When the proposed antenna is to be located at the top position (normal using mode), it is seen that the 1 g mass SAR re-sults at all frequencies meet the SAR limit of 1.6 mW/g. We can also observe that the difference between the measured SAR at the top and bottom positions is large. Obviously, this is due to the high current den-sity concentration around the antenna. In general, the SAR passive test is only a preliminary measurement and the test results are used to ana-lyze the antenna. In practical application, SAR is finally tested with an active device which may result in a different SAR value due to extra device elements.

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TABLE III

THELIQUIDPROPERTY OFPHANTOM

TABLE IV

THEMEASUREDSAR RESULTS IN1-gOF THESIMULATEDTISSUEFROM

EXPOSURE TO THEANTENNARADIATIONWITHTWOCASES OF THEPROPOSED

ANTENNA TOLOCATE AT THETOP ANDBOTTOMPOSITIONS OF THEHANDSET

BODY

IV. CONCLUSION

In this communication, the proposed hexa-band antenna is practi-cally capable to operate at the CDMA, GSM, DCS, PCS, WCDMA and Bluetooth bands. We demonstrated that a printed asymmetric T-type monopole with a solid shorting-line and a solid open-stub structure pro-vides the hexa-band operation. By correctly choosing the shorting-line parameters and by modifying the shape of the T-type monopole arms, two bandwidths, 17.8% and 37.1%, can be obtained. The contribution of this communication is to implement a simple and low profile antenna for the practical mobile handset application. Measurement results show that a broad bandwidth is obtained. Although this antenna is designed for mobile handset applications, this design concept can be extended to the antenna design for laptop computers.

ACKNOWLEDGMENT

The authors would like to thank Prof. C.-Y. Wu (IEEE Life Fellow, Dept. of E.E, Jinwen University of Science and Technology), Prof. C.-W. Hsue (IEEE Fellow, Dept. of E.E, National Taiwan University of Science and Technology) for their help. The authors also appreciate the reviewer’s comments to improve the quality of this communication.

REFERENCES

[1] Ramiro and Chaouki, “Wireless communications and networking: An overview,” IEEE Antennas Propag. Mag., vol. 44, pp. 185–193, Feb. 2002.

[2] C.-H. Chang and K.-L. Wong, “Printed 8-PIFA for penta-band WWAN operation in the mobile phone,” IEEE Trans. Antennas Propag., vol. 57, pp. 1373–1381, May 2009.

[3] J. D. Kraus and R. J. Marchefka, Antennas, 3rd ed. New York: Mc Graw-Hill, 2002, pp. 804–805.

[4] K.-L. Wong, G. Y. Lee, and T.-W. Chiou, “A low-profile planar monopole antenna for multiband operation of mobile handsets,” IEEE Trans. Antennas Propag., vol. 51, no. 1, pp. 121–125, Jan. 2003.

[5] Z. Li and Y. Rahmat-Samii, “Optimization of PIFA-IFA combination in handset antenna design,” IEEE Trans. Antennas Propag., vol. 53, pp. 1770–1777, May 2005.

[6] P. Vainikainen, J. Ollikainen, O. Kivekäs, and I. Kelander, “Res-onator-based analysis of the combination of mobile handset antenna and chassis,” IEEE Trans. Antennas Propag., vol. 50, no. 10, pp. 1433–1444, Oct. 2002.

[7] A. Cabedo, J. Anguera, C. Picher, M. Ribó, and C. Puente, “Multi-band handset antenna combining a PIFA, slots, and ground plane modes,” IEEE Trans. Antennas Propag., vol. 57, no. 9, pp. 2526–2533, Sep. 2009.

[8] R. Hossa, A. Byndas, and M. E. Bialkowski, “Improvement of com-pact terminal antenna performance by incorporating open-end slots in ground plane,” IEEE Microw. Wireless Compon. Lett., vol. 14, no. 6, Jun. 2004.

[9] J. Anguera, I. Sanz, A. Sanz, A. Condes, D. Gala, C. Puente, and J. Soler, “Enhancing the performance of handset antennas by means of groundplane design,” presented at the IEEE Int. Workshop on Antenna Technology: Small Antennas and Novel Metamaterials (iWAT 2006), New York, Mar. 2006.

[10] C. Picher, J. Anguera, A. Cabedo, C. Puente, and S. Kahng, “Multiband handset antenna using slots on the ground plane: Considerations to fa-cilitate the integration of the feeding transmission line,” Progr. Elec-tromagn. Res. C, vol. 7, pp. 95–109, 2009.

[11] C.-M. Peng, I.-F. Chen, and C.-W. Hsue, “Modified printed folded 8 dipole antenna for DVB applications,” IEICE Trans. Commun.., vol. E90-B, pp. 2991–2994, Oct. 2007.

[12] I.-F. Chen, C.-M. Peng, and S.-C. Liang, “Single layer printed monopole antenna for dual ISM-band operation,” IEEE Trans. An-tennas Propag., vol. 53, no. 4, pp. 1270–1273, Apr. 2005.

[13] Schmid and Partner Engineering, AG (SPEAG) [Online]. Available: http://www.speag.com/speag/products.php