A Band Reconfigurable Antenna for a Mobile Phone with the Metal Cover

Jui-Han Lu, Syue-Yi Syu and Yong-Yong Zhang

Department of Electronic Communication Engineering, National Kaohsiung University of Science and Technology, Kaohsiung, Taiwan

Abstract - This work proposes dual inverted-F antennas (IFAs) to obtain multi-band reconfigurable operation for a LTE/WWAN mobile phone with the metal cover. The impedance bandwidths across dual operating bands approach the bandwidth specification of the LTE / WWAN bands, respectively. The measured peak gains and antenna efficiencies are approximately 0.2 / 2.2 / 1.0 dBi and 36 / 55 / 66 % across the LTE/WWAN bands, respectively.

Index Terms —LTE, WWAN, Reconfigurable.

1. Introduction

The long term evolution (LTE) system with three operating bands in the LTE700 (698 ~ 787 MHz), LTE2300 (2300 ~ 2400 MHz) and LTE2500 (2500 ~ 2690 MHz) has integrated into the 4G communication technology to support dual wideband operations in the mobile devices and provide the significantly higher data rate than that of 3G wireless wide area network (WWAN) operations. Recently, several LTE/WWAN antennas have been presented [1-6] by using the metal rims of a mobile device to maximize the visual screens. And, matching circuits are introduced to integrated with the metal casing of the tablet or handset [1, 3-5]. However, the above antenna designs [1-3] have larger ground clearance. Then, this work proposes dual inverted-F antennas (IFAs) to obtain low/high band reconfigurable operation and meet the bandwidth specification of LTE/WWAN systems. A switch IC is introduced into the low-band IFA to adjust the operating frequency of LTE700 and GSM900 bands. To comply with the SAR requirement, this work also analyzes the simulated body SAR results of the proposed IFA antennas. Details of the proposed antenna design are described in this study, and the related results for the obtained performance operated across LTE/WWAN bands are presented and discussed.

2. Antenna design and experimental results

Fig. 1 illustrates the geometry of the proposed dual inverted-F antennas with band-reconfigurable operation for a LTE/WWAN mobile phone with the metal cover. The low-band inverted-F antenna is comprised of the metal frame connecting with the step-shaped metal strip and coupled-fed with a π-shaped LC circuit to obtain better impedance matching across LTE700/GSM/UMTS bands. In this study, a switch IC (CXA4447GC) is added at the end of step-shaped metal strip to adjust LTE700/GSM850/900 operating band. Then, the high-band

inverted-F antenna is directly fed with a L-shaped matching circuit to excite LTE2500/3500 MHz bands.

(a) Front view (b) Back view

Fig. 1. Geometry of the proposed dual inverted-F antennas in a LTE/WWAN mobile phone with the metal cover.

To demonstrate the above deduction and guarantee the

correctness of simulated results, the electromagnetic simulator HFSS based on the finite element method [7] has been applied for the proposed dual inverted-F antennas. Fig. 2(a) shows the related simulated and experimental return loss for the proposed dual inverted-F antennas. From the experimental results, by switching the feed point A or A’, the measured impedance bandwidths (RL ≥ 6 dB) can meet the band specification of LTE700 / GSM900 / LTE2500 / 3500 MHz operating bands, respectively. The band reconfigurable operation across LTE700 and GSM900 MHz bands is shown in the Fig. 2(b). It is shown that the operating frequency can be adjusted by a switch IC to meet the bandwidth specification of LTE700/GSM900 MHz band. The 3D radiation patterns of the proposed dual inverted-F antennas are measured in anechoic chamber by using NSI-800F system with Agilent PNA N5230A. Fig. 3 shows the measured peak gains and efficiencies of the

Low-band Antenna

2018 International Symposium on Antennas and Propagation (ISAP 2018)October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea

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proposed dual inverted-F antennas. The maximum measured peak antenna gains and efficiencies are 0.2 / 2.2 / 1.0 dBi and 36 / 55 / 66 % across LTE/WWAN bands, respectively.

(a)

(b)

Fig. 2 Simulated and measured results against frequency for the proposed dual inverted-F antennas in a mobile phone with the metal cover.

(a)

(b)

Fig. 3. Simulated and measured peak gains and efficiencies across the operating bands for the proposed dual inverted-F antennas.

3. Conclusions

A novel dual inverted-F antennas with band reconfigurable operation for a LTE /WLAN mobile phone has been proposed and investigated. It provides enough impedance bandwidth for LTE/WWAN operating bands. Also, the proposed antenna provides maximum peak antenna gains and efficiencies of 0.2 / 2.2 / 1.0 dBi and 36 / 55 / 66 % across LTE/WWAN bands, respectively.

References

[1] Y.-L. Ban, Y.-F. Qiang, H. Wang, and K.-L. Wong, “A reconfigurable narrow-frame antenna for LTE/WWAN metal-rimmed smartphone applications,” IET Microw., Antennas Propag., vol. 10, no. 10, pp. 1092–1100, Jul. 2016.

[2] Y. L. Ban, Y. F. Qiang, Z. Chen, K. Kang, and J. H. Guo, “A dual-loop antenna design for Hepta-band WWAN/LTE metal-rimmed smartphone applications,” IEEE Trans. Antennas Propag., vol. 63, no. 1, pp. 48–58, Jan. 2015.

[3] K.-L. Wong and M.-T. Chen, “Very-low-profile dual-wideband loop antenna for LTE tablet computer,” Microw. Opt. Technol. Lett., vol. 57, no. 1, pp. 141–146, Jan. 2015.

[4] K.-L. Wong and C.-Y. Tsai, “IFA-based metal-frame antenna without ground clearance for the LTE/WWAN operation in the metalcasing tablet computer,” IEEE Trans. Antennas Propag., vol. 64, no. 1, pp. 53–60, Jan. 2016.

[5] K.-L. Wong and Y.-J. Li, “Low-profile open-slot antenna with three branch slots for triple-wideband LTE operation in the metal framed smartphone,” Microw. Opt. Technol. Lett., vol. 57, no. 10, pp. 2231–2238, Oct. 2015.

[6] C.-K. Hsu and S.-J. Chung, “Compact multiband antenna for handsets with a conducting edge,” IEEE Trans. Antennas Propag., vol. 63, no. 11, pp. 5102–5107, Nov. 2015.

[7] http://www.ansoft.com/products/hf/hfss, Ansoft Corporation HFSS.

2018 International Symposium on Antennas and Propagation (ISAP 2018)October 23~26, 2018 / Paradise Hotel Busan, Busan, Korea

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