Coupled-fed Printed PIFA for Internal Eight-Band LTE/GSM/UMTS Mobile Phone

Transcription

1 Chinese Journal of Electronics Vol.23, No.1, Jan Coupled-fed Printed PIFA for Internal Eight-Band LTE/GSM/UMTS Mobile Phone CHEN Zhi 1, BAN Yongling 2,YINGLijun 2 and CHEN Jinhua 2 (1.National Key Laboratory of Science and Technology on Communication, University of Electronic Science and Technology of China, Chengdu , China) (2.Institute of Electromagnetics, University of Electronic Science and Technology of China, Chengdu , China) Abstract A coupled-fed printed PIFA (Planar Inverted-F antenna) for eight-band operation covering the LTE700/2300/2500 and GSM850/900/1800/ 1900/UMTS2100 bands in the mobile phone is presented. The proposed antenna comprises a driven T-monopole and two coupled folded-strips. The folded strip which is coplaner with the T-monopole is called strip 1 and the folded-strip on the back of the system circuit board is called strip 2. The strip 1 is short-circuited to the system ground through an inductance and the Strip 2 is short-circuited to the system ground plane of the mobile phone directly. The driven T-monopole and the strip 1 contribute a wide band for the antenna s upper band ( MHz), whereas the strip 2 generates a resonant mode for the antenna s lower band ( MHz). The antenna s two wide operating bands are achieved and controlled by tuning the width of the T-monopole, the gap g3 between the strip 1 and the T-monopole, and the dimensions of the strip 2 on the back of the system circuit board. Details of the proposed antenna are described, and the obtained results are presented and discussed. Key words Mobile phone antennas, Printed antennas, Internal antennas, Coupled-fed. I. Introduction A continuously increasing number of communication systems are integrated in mobile devices, which means that mobile terminal antennas need to be able to operate at a wide range of different frequencies, accordingly. Long term evolution (LTE) [1,2] can provide better mobile broadband and multimedia services than the existing GSM and UMTS mobile networks. It is expected that in the very near future the LTE will be incorporated with the existing GSM/UMTS operation in the mobile phone. For this expectation, the internal mobile phone antenna should cover the additional three operating bands of the LTE, which include the LTE700 ( MHz), LTE2300 ( MHz), and LTE2500 ( MHz). That is, eight-band which include the LTE700 ( MHz), GSM850 ( MHz), GSM900 ( MHz), GSM1800 ( MHz), GSM1900 ( MHz), UMTS2100 ( MHz), LTE2300 ( MHz), and LTE2500 ( MHz) bands will be required for the internal mobile phone antennas. Nowadays thin-profile mobile phones are becoming more and more popular on the market. For such mobile phone applications, thin-profile internal antennas become a necessity. Most patch PIFA with a thickness of 3-4 mm, about one half of that of the conventional internal patch PIFAs (Planar Inverted-F antenna) [3,4], are very difficult to cover all the five operating bands of GSM850/GSM900/GSM1800/GSM1900/ UMTS2100, not to mention eight operation bands. This is owing to the small distance between the radiating patch and the ground plane, causing large coupling between the radiating patch and the ground plane and hence limiting the achievable bandwidth. Printed antennas which are printed directly on the no-ground portion of the system circuit board can solve this problem effectively [5 15]. This kind of antenna is an allprinting structure, hence it is easy to fabricate at low cost and is especially suited for thin-profile mobile phone applications. In this article, we present a promising coupled-fed printed PIFA to cover the eight-band LTE/GSM/UMTS operation. The proposed antenna comprises a driven T-monopole, the strip 1 which is short-circuited to the system ground through an inductance [16], and the Strip 2 which is short-circuited to the system ground plane of the mobile phone directly. For the T-monopole and strip1, a wideband (1800MHz 3000MHz) is generated. What s more, they can generate a resonant path to provide a resonant mode at about 700 MHz. For the T- monopole and the strip 2, resonant modes at about 650 MHz and 900MHz are excited, and the impedance matching over the upper band is improved. The proposed antenna is suitable to be directly printed on the system circuit board of the mobile phone, making it easy to fabricate at low cost and attractive for slim mobile phone applications. Details of the proposed antenna are studied in the article. II. Proposed Antenna Configuration The geometry of the proposed antenna for eight-band LTE/GSM/UMTS operation in the mobile phone is shown in Fig.1(a), and detailed dimensions of the metal pattern of Manuscript Received Aug. 2011; Accepted May 2012.

2 200 Chinese Journal of Electronics 2014 the antenna are given in Fig.1(b). The antenna is formed by the T-monopole, the strip 1 which is directly printed on the no-ground portion (size15 60mm 2 ),andthestrip2whichis printed on the reverse side of the system ground. The strip 1 and strip 2 have uniform width w1 =1mmandw2 =0.6mm, respectively. The gap g1 and g2 in the wrapped structure in the strip 1 and strip 2 are 1mm and 0.6mm, respectively. The gap g3 between the strip 1 and the T-monopole is 0.5mm. The T-monopole includes a rectangle patch and a triangle structure. In this study, the system circuit board with dimensions of mm 2 is made from a 0.8-mm thick FR4 substrate of relative permittivity 4.4 and loss tangent A plastic casing, which is made of a 1-mm-thick plastic plate with relative permittivity 3.0 and loss tangent 0.01, encloses the system circuit board to simulate the practical mobile phone casing. The plastic housing is chosen to have a thickness of 10mm in the study, and the system circuit board is arranged to be at the center of the plastic housing. The selected dimensions of the ground plane and circuit board are reasonable for practical mobile phones. The antenna can provide eight-band LTE/GSM/UMTS operating bands: the lower band covering the LTE700/GSM 850/900 ( MHz) with return loss better than 6dB and the upper band covering the GSM1800/1900/UMTS ( MHz) with return loss better than 6dB and the 2.4 GHz WLAN ( MHz) with return loss better than 10dB. The T-monopole itself can function as efficient quarterwavelength radiator to generate a resonant mode at about 2400 MHz for the antenna s upper band. The closed coupling structure formed by the strip 1 and the T-monopole though a small gap g3 can achieve good impedance matching over the upper band. As a result, a wideband (1800 MHz 3000 MHz) operation is obtained. What s more, the strip 1 can generate a resonant path to provide a resonant mode at about 700 MHz. The strip 2 is meandered to achieve a compact structure. Owing to the coupling effect between two adjacent meandered sections, the effective electrical length will be less than the physical length. This is largely the reason that the strip 2 length of branch is large than required 0.25λ. Thestrip 2 contributes most of the lower band ( MHz) operation. The triangle structure (see Fig.1) can help to achieve good impedance matching for frequencies over both the lower band ( MHz) and the upper band. Hence, the wider band can be achieved. The impedance matching over the lower and upper bands can be controlled by adjusting gap g3 inthe coupling feed. III. Results and Discussion Fig.2 shows the measured and simulated return loss of the proposed antenna. The measured data are observed to agree with the simulated results obtained by Ansoft simulation software HFSS version 12. With 3:1 VSWR definition which is widely used for practical internal mobile phone antenna design, the lower band has a wide bandwidth covering the desired MHz band. The upper band has an even wider bandwidth of larger than 980 MHz covering the desired MHz band. That is, the proposed antenna can cover the eight-band LTE/GSM/UMTS operation. Fig. 2. Simulated and measured return loss of the proposed antenna Fig. 1. (a) Geometry of the coupled-fed printed PIFA for the LTE/GSM/UMTS operation in the mobile phone; (b) The metal pattern of the proposed antenna The comparison between the proposed antenna and the antenna without the triangle structure is studied in Fig.3. Obviously, the triangle structure (see Fig.1) can help to improving the impedance matching for frequencies over both the lower band ( MHz) and the upper band. The operating principle is analyzed in Fig.4 in which results of the simulated return loss of the proposed antenna,

3 Coupled-fed Printed PIFA for Internal Eight-Band LTE/GSM/UMTS Mobile Phone 201 the case Ref1 with the driven T-monopole only, the case Ref2 with the driven T-monopole and the strip 2, the case Ref3 with driven T-monopole and the strip 1, and the case with the proposed antenna. The corresponding dimensions of the antennas in above cases are the same as those of the proposed antenna. For the case Fef1, a wide resonant mode is seen to occur at about 2400 MHz, and the impedance matching of this resonant mode still needs to be improved. For the case Ref2, a wideband (1800 MHz 3000 MHz) is generated. What s more, a resonant mode to provide a resonant patch at about 700 MHz is generated. For Ref3, resonant modes at about 650 MHz and 900 MHz are excited, and the impedance matching over the upper band is improved. For the proposed antenna, it incorporates the resonances and generates the lower band ( MHz) and the upper band ( MHz). from 0.3 to 0.9mm is shown in the Fig.5. In the figure, it is observed that coupling gap g3 take large effects on the impedance matching of the proposed antenna at both lower and upper band. When g3 < 0.4mm, the impendence matching in lower band goes bad drastically. Good impedance matching of the proposed antenna can be achieved by adjusting the gap g3. Fig. 5. Simulated return loss as a function of coupling gap g3 Fig. 3. Simulated return loss of the proposed antenna and the antenna without triangle structure Fig. 6. Photos of the manufactured proposed antenna: Top side and (b) Backside (a) The measured 3D total-power radiation patterns for the proposed antenna are shown in Fig.7. Similar to the most mobile phone antenna, dipole-like radiation pattern with omnidirectional radiation in the azimuthal plane (x-y plane) at 824 MHz and 915 MHz in the lower band is seen. This is mainly owing to the system ground plane contributes much to the radiation in the antenna s lower band. For the higher fre- Fig. 4. Simulated return loss of the propoesd antenna, the case Ref1 with the driven T-monopole only, the case Ref2 with the driven T-monopole and strip 2, the case Ref3 with driven T-monopole and strip 1 Effects of varying the coupling gap g3 in the coupling feed are analyzed in Fig.5. The simulated return loss for g3 varied Fig. 7. Measured 3D total-power radiation patterns for the proposed antenna

4 202 Chinese Journal of Electronics 2014 quencies at 1750, 1920, and 2410 MHz, much more variations are seen in the radiation patterns. The obtained patterns show no special distinctions to those of the printed internal mobile phone antennas. The measured radiation efficiency for the proposed antenna is presented in Fig.8. The radiation efficiency is about 45% 85% for the lower band and 55% 88% for the upper band, respectively. The radiation frequencies are all better than 45% over the eight operating bands, which are acceptable for practical mobile phone applications. Fig. 8. Measured radiation efficiency for the proposed antenna. (a) The lower band ( MHz); (b) The upper band ( MHz) IV. Conclusions A coupled-fed printed PIFA for eight-band operation covering the LTE700/2300/2500, GSM850/900/1800/1900, and UMTS bands in the mobile phone is proposed. The proposed antennacomprisedat-monopoleandafoldedstrip1whichis printed on the no-ground portion directly (size 15 60mm 2 ), and a folded strip 2 which printed on the reverse side. Good radiation characteristics over the operating bands have also been achieved. The proposed antenna is printed on the system circuit board of the mobile phone directly, making it easy to fabricate at low cost and attractive for slim mobile phone applications. References [1] P. Xu, J. Wang, F. Qi, et al., An enhanced EM/SAGE-based H-infinity channel estimator for MIMO-OFDM systems, Chinese Journal of Electronics, Vol.20, No.4, pp , [2] H. Zhang and X. Dai, Time-variant channel estimation and symbol detection for MIMO/OFDM systems using superimposed training, Chinese Journal of Electronics, Vol.19, No.3, pp , [3] M.Z. Azad and M. Ali, A miniaturized Hilbert PIFA for dualband mobile wireless applications, IEEE Antennas Wireless Propag Lett, Vol.4, pp.59 62, [4] C.W. Chiu and F.L. Lin, Compact dual-band PIFA with multiresonators, Electronic Lett., Vol.38, No.12, pp , [5] K.L. Wong and W.Y. Chen, Small-Size Printed Loop-Type Antenna Integrated With Two Stacked Coupled-Fed Shorted Strip Monopoles For Eight-Band LTE/GSM/UMTS Operation In The Mobile Phone, Microwave Opt Technol Lett, Vol.52, No.7, pp , [6] W.Y. Chen and K.L. Wong, Small-size coupled-fed shorted T-monopole for internal WWAN antenna in the slim mobile phone, Microwave Opt Technol Lett, Vol.52, pp , [7] G. Wen, Q. Rao, S. Ali, et al., Handset antenna design: Practice and theory, Progress In Electromagnetics Research, Vol.80, pp , [8] Z. Zhang, W. Chen, Z. Feng, et al., Integrated dual-band antenna system design incorporating cell phone bezel, IEEE Antennas Wireless Propag Lett, Vol.7, pp , [9] Y.W. Chi and K.L. Wong, Internal compact dual-band printed loop antenna for mobile phone application, IEEE Trans Antennas Propag, Vol.55, No.5, pp , [10] J.H. Chen, Y.L. Ban, H.M. Yuan, et al., Printed coupledfed PIFA for seven-band GSM/UMTS/LTE WWAN mobile phone, J. of Electromagn. Waves and Appl., Vol.26, pp , [11] Y.L. Ban, C.Q. Lei, J.H. Chen, et al., Compact coupled-fed PIFA employing T-shaped monopole with two stubs for eightband LTE/WWAN in internal mobile phone, J. of Electromagn. Waves and Appl., Vol.26, pp , [12] Z. Chen, Y.L. Ban, J.H. Chen, L.W. Li and Y.J. Wu, Bandwidth enhancement of LTE/WWAN printed mobile phone antenna using slotted ground structure, Progress In Electromagnetics Research, Vol.129, pp , [13] Y.L. Ban, J.H. Chen, S.C. Sun, et al., Printed ultrawideband antenna with chip-capacitor-loaded inductive strip for LTE/GSM/UMTS WWAN wireless USB dongle application, Progress in Electromagnetics Research, Vol.128, pp , [14] Y.L. Ban, H.M. Yuan, J.H. Chen, et al., A novel ultrawideband antenna with distributed inductance for wireless USB dongle attached to laptop computer, J. of Electromagn. Waves and Appl., Vol.26, pp , [15] Y.L. Ban, J.H. Chen, L.W. Li, et al., Printed ultra-wideband antenna for LTE/GSM/UMTS wireless USB dongle applications, IEEE Antennas Wireless Propag. Lett., Vol.11, No.1, pp , [16] T.W. Kang and K.L. Wong, Chip-inductor-embedded smallsize printed strip monopole for WWAN operation in the mobile phone, Microwave Opt Technol Lett, Vol.51, No.4, pp , CHEN Zhi received B.E., M.E., and Ph.D. degrees in Electrical Engineering from University of Electronic Science and Technology of China (UESTC), in 1997, 2000, 2006, respectively. On April 2006, he joined the National Key Lab of Science and Technology on Communications (NCL), UESTC, and worked as associate professor in this lab from August He was a visiting scholar at University of California, Riverside during His current research interests include wireless communication and signal processing, microwave communication, and THz communication. Dr. Chen has served as a reviewer for various international journals and conferences, including IEEE Transactions on Vehicular Tech-

5 Coupled-fed Printed PIFA for Internal Eight-Band LTE/GSM/UMTS Mobile Phone 203 nology, IEEE Transactions on Signal Processing, etc. ( BAN Yongling (corresponding author) received B.S. degree, M.S. degree, and Ph.D. degree in mathematics from Shandong University, in electromagnetics from Peking University, and in microwave engineering from University of electronic science and technology of China (UESTC), in 2000, 2003, and 2006, respectively. In July of 2006, he joined the Institute of Xi an mechanical and electrical information from China North Industries Group Corporation, as a microwave engineer. Half year later, he moved to Huawei Technologies Co., LTD. in Shenzhen, first as a RF antenna design engineer and then to senior design engineer. In Huawei, he designed and implemented various antennas for 15 data card and mobile phone products customized from leading telecommunication industries like Vodafone. From August of 2010 to present, he has served as an associate professor in the department of microwave engineering from University of Electronic Science and Technology of China (UESTC). His research and development interests include wideband small antenna for 3G/LTE handheld and mobile devices, directional patch antennas and arrays for mobile small base station, MIMO antenna decoupling techniques, and reducing interactions between small antennas and users (such as head, hand). He holds 11 granted and pending China and overseas patents, and he is the author of over 30 referred journal and conference papers on these topics. ( byl@uestc.edu.cn) ylj195@163.com) YING Lijun received the B.S. degree from Shandong University of Technology, China, in 2009, and the M.S. degree from University of Electronic and Science Technology of China (UESTC), China, in 2012 respectively. He is currently with Huawei Technologies Co., Ltd., Shenzhen, China. His research interests include wideband mobile terminal antennas, and MIMO decoupling techniques. ( CHEN Jinhua received the B.S. degree from West Anhui University, China, in 2009, and the M.S. degree from University of Electronic and Science Technology of China (UESTC), China, in 2012 respectively. He is currently with Huawei Technologies Co., Ltd., Chengdu, China. His research interests include. mobile terminal antennas, and microwave passive and active circuits. ( 2008jhchen@163.com)