Bandwidth Enhancement of Small-Size Planar Tablet Computer Antenna Using a Parallel-Resonant Spiral Slit

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 4, APRIL 2012 1705 Bandwidth Enhancement of Small-Size Planar Tablet Computer Antenna Using a Parallel-Resonant Spiral Slit Kin-Lu Wong, Fellow, IEEE, Yu-Wei Chang, and Shu-Chuan Chen, Student Member, IEEE Abstract An internal planar tablet computer antenna having a small size of printed on a 0.8-mm thick FR4 substrate for the WWAN operation in the 824 960 and 1710 2170 MHz bands is presented. The antenna comprises a driven strip, a parasitic shorted strip and a ground pad, all printed on the small-size FR4 substrate. For bandwidth enhancement of the antenna s lower band, the antenna applies a parallel-resonant spiral slit embedded in the ground pad, which generates a parallel resonance at about 1.2 GHz and in turn results in a new resonance occurred nearby the quarter-wavelength mode of the parasitic shorted strip. This feature leads to a dual-resonance characteristic obtained for the antenna s lower band, making it capable of wideband operation to cover the desired 824 960 MHz with a small antenna size. The antenna s upper band is formed by the higher-order resonant mode contributed by the parasitic shorted strip and the quarter-wavelength resonant mode of the driven strip and can cover the desired 1710 2170 MHz band. Details of the proposed antenna and the operating principle of the parallel-resonant spiral slit are presented. Index Terms Mobile antennas, parallel-resonant spiral slit, printed antennas, tablet computer antennas, WWAN antennas. I. INTRODUCTION T O obtain wideband operation with a small antenna size is one of the major design challenges of the internal WWAN (wireless wide area network) antennas for application in the mobile devices such as the mobile handsets and tablet computers. This design challenge is even critical for the WWAN antennas for application in the tablet computers than in the mobile handsets. This is because the ground plane supporting the display panel in the tablet computer is generally much larger than that in the mobile handsets and generally cannot support the chassis (ground plane) mode as in the mobile handset [1] [4] to aid in enhancing the operating bandwidth of the antenna, especially the bandwidth at about 900 MHz. Hence, it is noted that the reported internal WWAN antennas for the tablet or laptop com- Manuscript received June 18, 2011; revised August 19, 2011; accepted October 17, 2011. Date of publication January 31, 2012; date of current version April 06, 2012. K.-L.WongandS.-C.ChenarewiththeDepartmentofElectricalEngineering, National Sun Yat-sen University, Kaohsiung, Taiwan (e-mail: wongkl@ema.ee.nsysu.edu.tw; wongkl@mail.nsysu.edu.tw; chensc@ema.ee. nsysu.edu.tw). Y.-W. Chang was with the Department of Electrical Engineering, National Sun Yat-sen University, Kaohsiung, Taiwan. He is now with the Network Access Strategic Business Unit, Lite-On Technology Corporation, Taipei, Taiwan (e-mail: changyw@ema.ee.nsysu.edu.tw). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TAP.2012.2186266 TABLE I ANTENNA DIMENSIONS OF TYPICAL WWAN LAPTOP COMPUTER ANTENNAS IN RECENT ARTICLES., AND STAND FOR THE HEIGHT, WIDTH AND THICKNESS OF THE ANTENNA DIMENSIONS. THE PLANAR STRUCTURES INDICATE THAT THE ANTENNA IS PRINTED ON A DIELECTRIC SUBSTRATE, WHILE THE 3-D STRUCTURE INDICATES THAT THE ANTENNA IS INA THREE-DIMENSIONAL CONFIGURATION puters are generally required to have a length of about 50 mm or larger to be mounted along the top edge of the display ground to cover the GSM850/900 operation (824 960 MHz) and the GSM1800/1900/UMTS operation (1710 2170 MHz) [4] [14]. Table I lists the dimensions of typical WWAN laptop computer antennas in recent articles. The thickness of 0.8 mm for the planar structure is the thickness of the dielectric substrate on which the antenna is printed. In this paper, we present a small-size planar WWAN tablet computer antenna that is easy to fabricate on a thin FR4 substrate of size and is able to provide two wide operating bands to cover the desired 824 960 and 1710 2170 MHz bands. The required antenna size for the WWAN operation is smaller than those of the related internal WWAN antennas that have been reported [4] [14]. The antenna comprises a driven strip, a parasitic shorted strip and a ground pad, all printed on the small-size FR4 substrate. The wideband operation with a small antenna size is mainly obtained by embedding a parallelresonant spiral slit in the ground pad. The spiral slit can generate an anti-resonant mode or a parallel resonance [15] at the high-frequency tail of the quarter-wavelength resonant mode contributed by the parasitic shorted strip. Owing to the parallel resonance, a new resonance (zero reactance) can occur at a frequency higher than the resonant frequency of the quarter-wavelength resonant mode of the parasitic shorted strip, thereby resulting in a new resonant mode occurred nearby to achieve the desired wide lower band for the antenna. For the wide upper band for the antenna, it is formed by the higher-order resonant modes contributed by the parasitic shorted strip and the quarter-wavelength resonant mode of the driven strip. 0018-926X/$31.00 2012 IEEE

1706 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 4, APRIL 2012 Note that, the spiral slit in this study causes a parallel resonance which is similar to the quarter-wavelength slit or half-wavelength slot that has been applied in the ultrawideband planar antennas [16] [21] to achieve band-notching of the 5.2/5.8 GHz WLAN bands in the ultrawideband operation (3.1 10.6 GHz) [22]. However, the parallel resonance generated by the proposed spiral slit is occurred at the high-frequency tail, close to but not within the operating band, of the existing resonant mode which is generally of a narrow bandwidth. This feature leads to a new resonance generated nearby the existing resonant mode, thereby resulting in a new resonant mode generated to combine with the existing one to form a wide operating band for the antenna s lower band, which mainly dominates the required size of the antenna. Detailed operating principle of the parallel-resonant spiral slit in enhancing the bandwidth of the antenna is addressed. The proposed antenna is also fabricated and tested. Results of the obtained antenna performances are presented and discussed. II. PROPOSED ANTENNA Fig. 1 shows the proposed small-size planar WWAN tablet computer antenna with a parallel-resonant spiral slit in the ground pad. The antenna is mounted at the shielding wall (size ) at the top of the display ground for tablet computer applications, with the ground pad connected to the display ground. Both the ground pad and display ground serve as the antenna ground in this study. The dimensions of the display ground are chosen to be for supporting a 9.7-inch display panel. The selected display ground dimensions are reasonable for the tablet computers on the market. The antenna is also placed close to one corner of the shielding wall withadistanceof15mm.thiscanallowmorepossibleinternal antennas to be mounted along the shielding wall in practical applications in which there are usually a variety of internal antennas required to be embedded in the tablet computer. The antenna is printed on a 0.8-mm thick FR4 substrate of size, relative permittivity 4.4 and loss tangent 0.024. On one side of the substrate, there are a driven strip and a parasitic shorted strip. The latter is short-circuited through a via-hole at point C to a ground pad of size printed on the other side of the substrate. In the ground pad, a spiral slit of length 50 mm and width 0.3 mm as shown in the figure is embedded. The open end of the spiral slit is at the side edge of the ground pad. For practical tablet computer application, the ground pad is grounded to the shielding wall at point D, and the antenna is fed using a 50- mini coaxial line, whose central conductor and outer grounding sheath are connected respectively to pointaandbasshowninthefigure. The antenna geometry can be seen more clearly from the photos of the fabricated prototype shown in Fig. 2. Note that the driven strip has a length of 33.5 mm,which can generate a quarter-wavelength resonant mode at about 1800 MHz. The parasitic shorted strip has a length of about 72 mm and is short-circuited to the antenna ground at point C as shown in the figure. The shorted strip can generate a quarter-wavelength resonant mode at about 850 MHz and a higher-order resonant mode at about 2200 MHz. The latter combines the Fig. 1. Geometry of the proposed planar WWAN tablet computer antenna with a parallel-resonant spiral slit in the ground pad. Fig. 2. Photos of the fabricated antenna. resonant mode generated by the driven strip to cover the desired GSM1800/1900/UMTS bands. Also note that the use of a narrow section (width 0.2 mm) of the shorted strip at the side edge of the substrate is expected to provide some additional inductance to the antenna s input impedance, which can help decrease the required length for generating the resonant mode at about 850 MHz. This is similar to the chip-inductor loading in the radiating strip to decrease the resonant length of the antenna [23] [25]. However, when the spiral slit is not present, the resonant mode at about 850 MHz is generally of a narrow bandwidth and is far from covering the desired GSM850/900 bands. By embedding the proposed spiral slit, a parallel resonance can occur at about 1200 MHz, which is at the high-frequency tail of the resonant mode at about 850 MHz and can lead to a new resonance generated at about 1000 MHz. This new resonance results in a new resonant mode generated to combine the resonant mode at about 850 MHz to form a wide operating band

WONG et al.: BANDWIDTH ENHANCEMENT OF SMALL-SIZE PLANAR TABLET COMPUTER ANTENNA 1707 Fig. 3. Measured and simulated return loss of the proposed antenna. Fig. 5. Simulated input impedance for the proposed antenna and Ant2 studied in Fig. 4. Fig. 4. Simulated return loss for the proposed antenna, the case with the driven strip only (Ant1), and the case with the driven strip and parasitic shorted strip only (Ant2). to cover the GSM850/900 operation. Also note that the parallel resonance generated by the spiral slit can be controlled by adjusting the length of the spiral slit, and more detailed results for the parallel-resonant spiral slit are given in Section III. III. RESULTS AND DISCUSSION Fig. 3 shows the measured and simulated return loss of the fabricated antenna shown in Fig. 2. The ground pad of the fabricated antenna is connected to the display ground as shown in Fig. 1 for testing in the experiment. The simulated results are obtained using the full-wave electromagnetic field simulation software HFSS version 12 [26]. The simulated results in general agree with the measured data. Two wide operating bands are obtained for the antenna to cover the desired 824 960 and 1710 2170 MHz bands (see the shaded region in the figure) for the WWAN operation. Note that in the desired operating bands, the impedance matching is better than 6-dB return loss (3:1 VSWR), which is the widely used design specification for the internal WWAN handset antennas. To analyze the operating principle of the antenna, Fig. 4 shows the simulated return loss for the proposed antenna, the case with the driven strip only (Ant1), and the case with the driven strip and parasitic shorted strip only (Ant2). For Ant1, a resonant mode is seen to occur at about 2000 MHz, although the impedance matching of this resonant mode is poor. By adding a parasitic shorted strip to form Ant2, a resonant mode at about 850 MHz is generated, which however shows a narrow bandwidth. A higher-order resonant mode at about 2200 MHz is also generated by the parasitic shorted strip, and the impedance matching of the resonant mode contributed by the driven strip is improved. By further embedding the proposed spiral slit in the ground pad to form the proposed antenna, a parallel resonance at about 1200 MHz is generated. This behavior can be seen more clearly in Fig. 5 in which the input impedance of the proposed antenna and Ant2 is shown for comparison. The parallel resonance at about 1200 MHz greatly modifies the input reactance of Ant2 at about 1000 MHz and leads to a new resonance (zero reactance) generated nearby the quarter-wavelength resonant mode contributed by the parasitic shorted strip. This behavior leads to a dual-resonance characteristic for the antenna s lower band seen in Fig. 4, which covers the desired 824 960 MHz. Also, the spiral slit slightly shifts the two resonant modes contributed by the driven strip and parasitic shorted strip to lower frequencies to cover the desired 1710 2170 MHz bands. In addition, as seen in Fig. 5, there is a second parallel resonance occurred at about 2800 MHz, which is contributed by the spiral slit and modifies the impedance matching of the resonant mode at about 2200 MHz contributed by the shorted strip to result in another new resonant mode generated at about 2400 MHz (the third mode in the antenna s upper band seen in Fig. 4). Fig. 6 shows the simulated surface current distributions on the antenna s metal pattern and the electric field strengths in the spiral slit at 850, 1000 and 1200. It is clearly seen that the shorted strip is excited at both 850 and 1000 MHz, and is not excited at 1200 MHz. On the other hand, strong electric fields are seen in the spiral slit at 1200 MHz, which confirms that a parallel resonance is generated by the spiral slit at 1200 MHz. Also, the electric field strengths are much weaker at 850 MHz than at 1000 MHz, while the surface currents on the driven strip are much stronger at 850 MHz than at 1000 MHz. This behavior suggests that the excitation of the shorted strip at 850 MHz is related to the driven strip, while that at 1000 MHz is related to the spiral slit.

1708 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 4, APRIL 2012 Fig. 6. Simulated surface current distributions on the antenna s metal pattern and electric field strengths in the spiral slit at 850, 1000 and 1200 MHz. Note that the occurrence of the two parallel resonances seen in Fig. 5 can be controlled by the length of the spiral slit. The first parallel resonance occurs when the length of the spiral slit is close to a quarter-wavelength of the parallel resonance frequency [16]. Owing to the presence of the FR4 substrate on which the spiral slit is printed, the required spiral length (50 mm in this study) is much lower than a free-space quarter-wavelength (about 62 mm) of the obtained parallel resonance frequency at 1200 MHz seen in the figure. Fig. 7 shows the simulated return loss and input impedance versus the length of the spiral slit. By decreasing the length of the spiral slit from 50 to 45 mm, the two parallel resonances are shifted to higher frequencies. Effects of the display ground size on the proposed antenna are also analyzed. Fig. 8 shows the simulated return loss for the proposed antenna with three different dimensions of the display ground. Small effects on the antenna s upper band are seen, while there are relatively large effects on the antenna s lower band. The obtained results indicate that although the display ground dimensions are much larger compared to the system ground plane of the mobile handset, there are still large groundplane effects on the 900-MHz band for the internal WWAN tablet computer antenna. This can be attributed to the large wavelength (about 33 cm) of the frequencies in the 900-MHz band compared to the dimensions of the display ground in the tablet computer. Fig. 9 shows the simulated return loss for the antenna in Fig. 1, the case of the antenna flushed to the side edge of the display ground (Case A in the figure), and a grounded metal box of size added nearby the antenna (10-mm to the antenna) in Case A (Case B in the figure). The dimensions of the three cases shown in the figure are all the same. Small effects are observed for the three cases, indicating that the antenna can be placed at the corner of the display ground and metal object can also be placed nearby the antenna. Fig. 10 shows the simulated return loss for the proposed antenna as a function of the length in the parasitic shorted strip. The length is the length of the open-end section of the parasitic shorted strip. By tuning the length, the two resonant modes contributed by the parasitic shorted strip can be adjusted, with Fig. 7. Simulated (a) return loss and (b) input impedance versus the length of the spiral slit. Fig. 8. Simulated return loss for the proposed antenna as a function of different dimensions of the display ground. the resonant mode at about 1800 MHz contributed by the driven strip almost not affected. It is also noted that the resonant mode at about 1000 MHz generated owing to the spiral slit is affected as well. This behavior is reasonable since the additional resonance (zero reactance) related to the resonant mode at about 1000 MHz is an effect caused by the generated parallel resonance of the spiral slit on the input impedance characteristic of the frequencies at the high-frequency tail of the resonant mode of the parasitic shorted strip. Fig. 11 shows the simulated return loss for the proposed antenna as a function of the length of the driven strip. By decreasing the length,thefirst resonant mode in the antenna s upper band is shifted to higher frequencies. This confirms that

WONG et al.: BANDWIDTH ENHANCEMENT OF SMALL-SIZE PLANAR TABLET COMPUTER ANTENNA 1709 Fig. 12. Measured antenna efficiency (mismatching loss included) of the proposed antenna. Fig. 9. Simulated return loss for the antenna in Fig. 1, the case of the antenna flushed to the side edge of the display ground (Case A), and a grounded metal plate added nearby the antenna in Case A (Case B). The antenna dimensions are all the same in this study. Fig. 10. Simulated return loss for the proposed antenna as a function of the length in the parasitic shorted strip. Fig. 13. Measured radiation patterns of the proposed antenna. Fig. 11. Simulated return loss for the proposed antenna as a function of the length of the driven strip. this resonant mode is contributed by the driven strip, and hence it can be controlled by adjusting the length of the driven strip. It is also observed that the shifting of this resonant mode causes some variations on the other resonant modes nearby, causing degraded impedance matching for frequencies in the antenna s upper band. Fig. 12 shows the measured antenna efficiency of the proposed antenna. The simulated results are also shown for comparison. The measurement is conducted in a far-field anechoic chamber, and the measured antenna efficiency includes the mismatching loss. The measured antenna efficiency varies from about 53% to 67% for frequencies over the GSM850/900 band, while that over the GSM1800/1900/UMTS band varies from about 54% to 76%. In the antenna s lower band, it is also seen that the antenna efficiency is still better than 40% for frequencies up to about 1025 MHz and is then quickly decreased for higher frequencies. The measured three-dimensional radiation patterns of the proposed antenna are shown in Fig. 13. At each testing frequency, which is respectively the center frequency of the five WWAN operating bands, three radiation patterns seen in different directions are shown. At frequencies (859 and 925 MHz) in the antenna s lower band, the radiation patterns are no longer close to dipole-like patterns. This is mainly owing to the much larger dimensions of the display ground compared to the system ground plane of the mobile handset [27] [29]. At higher frequencies (1795, 1920 and 2045 MHz) in the antenna s upper band, there are more dips and more variations in the radiation patterns, compared to those at lower frequencies. This behavior is related to more null surface currents excited on the display ground and is similar to the observations for the internal WWAN handset antennas [27] [29].

1710 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 60, NO. 4, APRIL 2012 IV. CONCLUSION The bandwidth enhancement technique of using a parallelresonant spiral slit to achieve a small-size penta-band WWAN tablet computer antenna has been proposed. The spiral slit is embedded in the ground pad of the proposed antenna and can be controlled to generate a parallel resonance at frequencies nearby an existing resonant mode at about 900 MHz. The generated parallel resonance can result in a new resonance occurred to generate an additional resonant mode, which combines the existing resonant mode to greatly enhance the bandwidth of the antenna s lower band. This makes it possible for the proposed antenna to cover the WWAN operation with a small size of only, which is about the smallest among the planar WWAN tablet computer or laptop computer antenna that have been reported. Good radiation characteristics for frequencies over the five WWAN operating bands have also been obtained for the proposed antenna. REFERENCES [1] P. Vainikainen, J. Ollikainen, O. Kivekas, and I. Kelander, Resonator-based analysis of the combination of mobile handset antenna and chassis, IEEE Trans. Antennas Propag., vol. 50, pp. 1433 1444, Oct. 2002. [2] T.Y.WuandK.L.Wong, Ontheimpedancebandwidthofaplanarinverted-F antenna for mobile handsets, Microwave Opt. Technol. Lett., vol. 32, pp. 249 251, Feb. 2002. [3] O. Kivekas, J. Ollikainen, T. Lehtiniemi, and P. Vainikainen, Effect of the chassis length on the bandwidth, SAR, and efficiency of internal mobile phone antennas, Microwave Opt. Technol. Lett., vol. 36, pp. 457 462, Mar. 2003. [4] C.H.ChangandK.L.Wong, Internal coupled-fed shorted monopole antenna for GSM850/900/1800/1900/UMTS operation in the laptop computer, IEEE Trans. Antennas Propag., vol. 56, pp. 3600 3604, Nov. 2008. [5] X. Wang, W. Chen, and Z. Feng, Multiband antenna with parasitic branches for laptop applications, Electron. Lett., vol. 43, pp. 1012 1013, Sep. 2007. [6] K. L. Wong and L. C. Lee, Multiband printed monopole slot antenna for WWAN operation in the laptop computer, IEEE Trans. Antennas Propag., vol. 57, pp. 324 330, Feb. 2009. [7] K. L. Wong, W. J. Chen, L. C. Chou, and M. R. Hsu, Bandwidth enhancement of the small-size internal laptop computer antenna using a parasitic open slot for the penta-band WWAN operation, IEEE Trans. Antennas Propag., vol. 58, pp. 3431 3435, Oct. 2010. [8] T.W.Kang,K.L.Wong,L.C.Chou,andM.R.Hsu, Coupled-fed shorted monopole with a radiating feed structure for eight-band LTE/WWAN operation in the laptop computer, IEEE Trans. Antennas Propag., vol. 59, pp. 674 679, Feb. 2011. [9] C. W. Chiu and Y. J. Chi, Printed loop antenna with a U-shaped tuning element for hepta-band laptop applications, IEEE Trans. Antennas Propag., vol. 58, pp. 3464 3470, Nov. 2010. [10] C. W. Chiu, Y. J. Chi, and S. M. Deng, An internal multiband antenna for WLAN and WWAN applications, Microwave Opt. Technol. Lett., vol. 51, pp. 1803 1807, Aug. 2009. [11] K. L. Wong and S. J. Liao, Uniplanar coupled-fed printed PIFA for WWAN operation in the laptop computer, Microwave Opt. Technol. Lett., vol. 51, pp. 549 554, Feb. 2009. [12] K. L. Wong and F. H. Chu, Internal planar WWAN laptop computer antenna using monopole slot elements, Microwave Opt. Technol. Lett., vol. 51, pp. 1274 1279, May 2009. [13] T. W. Kang and K. L. Wong, Internal printed loop/monopole combo antenna for LTE/GSM/UMTS operation in the laptop computer, Microwave Opt. Technol. Lett., vol. 52, pp. 1673 1678, Jul. 2010. [14] K. L. Wong and P. J. Ma, Coupled-fed loop antenna with branch radiators for internal LTE/WWAN laptop computer antenna, Microwave Opt. Technol. Lett., vol. 52, pp. 2662 2667, Dec. 2010. [15] Y. W. Chi and K. L. Wong, Very-small-size folded loop antenna with a band-stop matching circuit for WWAN operation in the mobile phone, Microwave Opt. Technol. Lett., vol. 51, pp. 808 814, Mar. 2009. [16] H. G. Schantz, G. Wolenec, and E. M. Myszka, III, Frequency notched UWB antennas, in Proc. 2003 IEEE Conf. on Ultra Wideband Systems and Technologies, Reston, VA, USA, pp. 214 218. [17] Y. Kim and D. H. Kwon, CPW-fed ultra wideband antenna having a frequency band notch function, Electron. Lett., vol. 40, pp. 403 405, Apr. 2004. [18] S. W. Su, K. L. Wong, and C. L. Tang, Band-notched ultra-wideband planar monopole antenna, Microwave Opt. Technol. Lett.,vol. 44, pp. 217 219, Feb. 2005. [19] K.L.Wong,Y.W.Chi,C.M.Su,andF.S.Chang, Band-notched ultra-wideband circular disk monopole antenna with an arc-shaped slot, Microwave Opt. Technol. Lett., vol. 45, pp. 188 191, May 2005. [20] S. W. Su and K. L. Wong, Printed band-notched ultra-wideband quasidipole antenna, Microwave Opt. Technol. Lett., vol. 48, pp. 418 420, Mar. 2006. [21] W. S. Lee, D. Z. Kim, K. J. Kim, and J. W. Yu, Wideband planar monopole antennas with dual band-notched characteristics, IEEE Trans. Microwave Theory Tech., vol. 54, pp. 2800 2806, Jun. 2006. [22]FirstReportandOrderintheMatterofRevisionofPart15ofthe Commission s Rules Regarding Ultra-Wideband Transmission Systems Federal Communications Commission, 2002, ET-Docket98-153. [23] C. H. Chang and K. L. Wong, Small-size printed monopole with a printed distributed inductor for penta-band WWAN mobile phone application, Microwave Opt. Technol. Lett., vol. 51, pp. 2903 2908, Dec. 2009. [24] K. L. Wong and S. C. Chen, Printed single-strip monopole using a chip inductor for penta-band WWAN operation in the mobile phone, IEEE Trans. Antennas Propag., vol. 58, pp. 1011 1014, Mar. 2010. [25] C. H. Chang and K. L. Wong, Bandwidth enhancement of internal WWAN antenna using an inductively coupled plate in the small-size mobile phone, Microwave Opt. Technol. Lett., vol. 52, pp. 1247 1253, Jun. 2010. [26] ANSYS HFSS [Online]. Available: http://www.ansys.com/products/hf/hfss/ [27] K. L. Wong, W. Y. Chen, and T. W. Kang, On-board printed coupled-fed loop antenna in close proximity to the surrounding ground plane for penta-band WWAN mobile phone, IEEE Trans. Antennas Propag., vol. 59, pp. 751 757, Mar. 2011. [28] F. H. Chu and K. L. Wong, Simple planar printed strip monopole with a closely-coupled parasitic shorted strip for eight-band LTE/GSM/ UMTS mobile phone, IEEE Trans. Antennas Propag., vol. 58, pp. 3426 3431, Oct. 2010. [29] F. H. Chu and K. L. Wong, Simple folded monopole slot antenna for penta-band clamshell mobile phone application, IEEE Trans. Antennas Propag., vol. 57, pp. 3680 3684, Nov. 2009. Kin-Lu Wong (M 91 SM 97 F 07) received the B.S. degree in electrical engineering from National Taiwan University, Taipei, Taiwan, and the M.S. and Ph.D. degrees in electrical engineering from Texas Tech University, Lubbock, in 1981, 1984, and 1986, respectively. From 1986 to 1987, he was a Visiting Scientist with Max-Planck-Institute for Plasma Physics in Munich, Germany. Since 1987 he has been with the Department of Electrical Engineering, National Sun Yat-Sen University (NSYSU), Kaohsiung, Taiwan, where he became a Professor in 1991. From 1998 to 1999, he was a Visiting Scholar with the ElectroScience Laboratory, The Ohio State University, Columbus. In 2005, he was elected to be the Sun Yat-sen Chair Professor of NSYSU. He also served as Chairman of the Electrical Engineering Department from 1994 to 1997, Dean of the Office of Research Affairs from 2005 to 2008, and now as Vice President for Academic Affairs, NSYSU (2007). He has published more than 500 refereed journal papers and 250 conference articles and has personally supervised 50 graduated PhDs. He also holds over 100 patents, including U.S., Taiwan, China, EU patents, and has many patents pending. He is the author of the books Design of Nonplanar Microstrip Antennas and Transmission Lines (Wiley, 1999), Compact and Broadband Microstrip Antennas (Wiley, 2002), and Planar Antennas for Wireless Communications (Wiley, 2003).

WONG et al.: BANDWIDTH ENHANCEMENT OF SMALL-SIZE PLANAR TABLET COMPUTER ANTENNA 1711 Dr. Wong was selected, in 2008, as one of the top 50 scientific achievements of the National Science Council of Taiwan in the past 50 years (1959 2009) for the research achievements of the Handheld Wireless Communication Devices Antenna Design of the NSYSU Antenna Lab that he led. He was awarded the 2010 Outstanding Research Award of Pan Wen Yuan Foundation and selected as top 100 honor of Taiwan by Global Views Monthly in August 2010 for his contribution in mobile communication antenna researches. He was awarded the Best Paper Award (APMC Prize) in 2008 Asia-Pacific Microwave Conference held in Hong Kong. His graduate students were the winners of Best Student Paper Awards in 2008 APMC, 2009 ISAP, and 2010 ISAP (International Symposium on Antennas and Propagation) and also won the first prize of 2007 and 2009 Taiwan National Mobile Handset Antenna Design Competition. He also serves as the General Chair of 2005 ISCOM (International Symposium on Communications) and 2012 APMC, both held in Kaohsiung, Taiwan. He received the Outstanding Research Award three times from National Science Council (NSC) of Taiwan in 1995, 2000 and 2002, and was elevated to be a NSC Distinguished Researcher in 2005. He also received the Outstanding Research Award from NSYSU in 1995, the ISI Citation Classic Award for a published paper highly cited in the field in 2001, the Outstanding Electrical Engineer Professor Award from Institute of Electrical Engineers of Taiwan in 2003, and the Outstanding Engineering Professor Award from Institute of Engineers of Taiwan in 2004. Yu-Wei Chang was born in Taichung, Taiwan. He received the B.S. degree in electrical engineering from National Taiwan Ocean University, Keelung, Taiwan, in 2009 and the M.S. degree in electrical engineering from National Sun Yat-sen University, Kaohsiung, Taiwan, in 2011. His main research interests are in antenna design for wireless communications, especially for the planar antennas for mobile devices, access points, WWAN and WLAN applications. He is currently an RF Antenna Engineer with Network Access Strategic Business Unit, Lite-On Technology Corporation, Taipei, Taiwan. Shu-Chuan Chen (S 10) was born in Changhua, Taiwan. She received the B.S. and M.S. degrees in electrical engineering from Chung-Cheng Institute of Technology, National Defense University, Taoyuan, Taiwan, in 1998 and 2004, respectively. She is now working toward the Ph.D. degree at National Sun Yat-sen University, Kaohsiung, Taiwan. Her main research interests are in internal antennas for mobile communication devices, especially for small-size multiband antennas in the mobile phones.