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IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 2, 2003
Miniature Built-In Quad-Band Antennas for Mobile Handsets Yong-Xin Guo, Member, IEEE, M. Y. W. Chia, and Z. N. Chen, Member, IEEE
Abstract—A new built-in quad-band handset antenna for covering GSM900, DCS1800, PCS1900, and UMTS2000 bands is presented. Details of the antenna are discussed along with measured and simulated results. The simulation is based on the finite-difference time-domain (FDTD) method. Index Terms—Antennas, built-in antennas, multiband antennas, planar inverted-F antennas (PIFAs).
I. INTRODUCTION
T
HE sizes and weights of mobile handsets have rapidly been reduced due to the development of modern integrated circuit technology and the requirements of the users. Conventional monopole-like antennas have remained relatively large compared to the handset itself. Thus, built-in antennas are becoming very promising candidates for applications in mobile handsets. Most built-in antennas currently used in mobile phones are based on planar inverted-F antennas (PIFAs) [1]. Basic PIFA elements are narrow in bandwidth. Currently, many mobile telephones use one or more of the following frequency bands: the GSM band, centered at 900 MHz; the DCS band, centered at 1800 MHz; and the PCS band, centered at 1900 MHz. Many interesting designs based on the PIFA concepts for achieving multiple-band operations have been available in open literatures [2]–[9]. Triple-band built-in antennas to operate at GSM900, DCS1800, and PCS1900 bands demonstrated in [7], [8] consist of a main radiator operating at a low-frequency band and a first high band and a shorted parasitic radiator operating at a second high band. The parasitic radiator lies in a plane parallel to and away from the main radiator and, therefore, occupies valuable space in mobile phones that are constantly shrinking in size. Furthermore, the parasitic-feed technique used for introducing one more mode may have problems in tuning of the antenna. More recently, it is envisaged that next generation mobile phones will require the capability to include the UMTS2000 band for 3G mobile applications as well, which was reported in [9]. In this letter,1 we propose a new design in that a new metal strip as an additional resonator is directly connected with a feed strip and positioned at a plane perpendicular to a ground plane and a main dual-resonator patch radiator. With this direct-feed scheme, the forgoing problems relating to the parasitic-feed technique for an additional resonance in a conventional Manuscript received January 15, 2003; revised February 19, 2003. The authors are with the Institute for Infocomm Research, Singapore 117674 (e-mail:
[email protected]). Digital Object Identifier 10.1109/LAWP.2003.811323 1A
U.S. patent (application number 10/281 226) is pending for this work.
Fig. 1.
Geometry of the new quad-band antenna.
Fig. 2. Measured and simulated return losses.
multiple-band antenna can be alleviated. As an example, a quad-band antenna for covering the GSM900, DCS1800, PCS1900, and UMTS2000 was achieved. The simulations were performed using Remcom software XFDTD5.3, which is based on the finite-difference time-domain (FDTD) method. II. ANTENNA STRUCTURE AND DESIGN The proposed new antenna in this work is shown in Fig. 1. The new radiating strip as an additional resonator is directly connected to the feed strip and positioned at a plane perpendicular to the ground plane and the original folded patch. The new antenna also comprises a folded radiating patch in the first layer, a ground plane in the second layer, a supporting foam in-between
1536-1225/03$17.00 © 2003 IEEE
GUO et al.: MINIATURE BUILT-IN QUAD-BAND ANTENNAS FOR MOBILE HANDSETS
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(a)
(b)
(c)
(d)
Fig. 3. Measured far-field radiation patterns at xz plane. (a) 925 MHz, (b) 1795 MHz, (c) 1935 MHz, (d) 2100 MHz. ——— E ,
a short-circuited strip, a feed strip, and a stub extended from the folded patch. The patch is connected to the ground plane via a vertical short-circuited strip and is fed via a feed strip connected to a 50- transmission line etched on the back of the ground plane. At the first layer, the long bent portion of the antenna is tuned to have a relatively low-band resonance frequency such as 900 MHz and the short part of the antenna is tuned to have a high-band resonance frequency such as 1800 MHz. The stub extended from the long bent portion is to finely tune the resonance at the low band. Compared to the designs in [7], [8], the size of the newly proposed antenna can be reduced by an order of 10 20%, which is desirable since the size of mobile phones is becoming smaller according to consumer preferences. The new additional strip is like a PIFA antenna and is tuned to have a second high resonance frequency, such as 2100 MHz. The new quad-band antenna was developed within the limits of a 36 16 8 mm area. The
0 0 0E
.
mm and a rectangular ground plane has a length of mm. The dimensions of the new antenna width of are mm, mm, mm, mm, mm, mm, mm, mm, mm, mm, mm, and mm. III. MEASURED AND SIMULATED RESULTS Fig. 2 shows the measured and simulated return losses of the new antenna. In the actual design, we need to consider around 5% frequency-shifting due to the effect of the plastic cover [7]. Thus, the simulated result with the plastic cover is also provided. In the simulation, a 2-mm-thick dielectric sheet with dielectric and 1-mm spacing between the cover and constant the antenna is used to simulate the actual effect of the plastic cover as in [7]. The measured bandwidths without the plastic
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cover according to 6-dB return loss matching are 78 MHz (933–1010 MHz) at the lower band and 516 MHz (1772–2288 MHz) at the upper band, respectively. The corresponding simulated results without the plastic cover are 130 MHz (924–1054 MHz) at the lower band and 486 MHz (1824–2310 MHz) at the upper band, respectively. A good agreement between measurement and simulation is obtained. Referring to Fig. 2, it is observed that there are some differences for the null depth in the simulated and measured return losses of the upper band, which may come from that the antenna size cannot be modeled very accurately by the FDTD method due to its meshing scheme. The simulated bandwidths with the plastic cover as in a real case are 126 MHz (883–1009 MHz) at the lower band and 573 MHz (1659–2232 MHz) at the upper band, respectively. The antenna has a capacity to cover the GSM900, DCS1800, PCS1900, and UMTS2000 bands. With regard to Fig. 2, the return loss has one distinct minimum at a low-frequency band and two minima at two high-frequency bands relatively close to each other. It is very clear to observe that the wide bandwidth of the higher band of the new antenna is due to the introduced strip connected to the feed. Note that the wide bandwidth at the upper band in this design may also come from one resonance generated by the ground plane, which has a half wavelength with the center frequency being around 1.8 GHz. The measured far-field radiation patterns of the new quad-band antenna without the plastic cover at 935 MHz, 1795 MHz, 1935 MHz, and 2100 MHz are depicted in Fig. 3(a)–(d), respectively. They are similar to those of other integrated antennas for mobile handsets [1]. It can also be seen that the measured gains for all bands are within 0 4 dBi. Referring to Fig. 3(a)–(d), the overall shape of the radiation patterns can be suitable for mobile communications terminals.
IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 2, 2003
IV. CONCLUSION In this letter, a built-in quad-band handset antenna for covering GSM900, DCS1800, PCS1900, and UMTS2000 bands has been presented. The antenna is also analyzed using the FDTD technique. A good agreement has been achieved between measurement and simulation.
REFERENCES [1] K. Fujimoto and J. R. James, Eds., Mobile Antenna Systems Handbook, 2nd ed. Norwood, MA: Artech House, 2001. [2] Z. D. Liu, P. S. Hall, and D. Wake, “Dual-frequency planar inverted-F antenna,” IEEE Trans. Antennas Propagat., vol. 45, pp. 1451–1457, Oct. 1997. [3] C. R. Rowell and R. D. Murch, “A compact PIFA suitable for dualfrequency 900/1800-MHz operation,” IEEE Trans. Antennas Propagat., vol. 46, pp. 596–598, Apr. 1998. [4] S. Tarvas and A. Isohatala, “An internal dual-band mobile phone antenna,” in IEEE Antennas and Propagation Symp. Dig., Salt Lake City, UT, July 2000, pp. 266–269. [5] R. Chair, K. M. Luk, and K. F. Lee, “Measurement and analysis of miniature multilayer patch antenna,” IEEE Trans. Antennas Propagat., vol. 50, pp. 244–250, Feb. 2002. [6] K. L. Wong, “A short course on planar antennas for wireless communications,” in Proc. IEEE Antennas and Propagation Society Int. Symp., San Antonio, TX, June 2002, pp. 6–14. [7] D. Manteuffel, A. Bahr, D. Heberling, and I. Wolff, “Design consideration for integrated mobile phone antennas,” in Proc. 11th Int. Conf. Antennas and Propagation, Manchester, U.K., Apr. 2001, pp. 252–256. [8] Z. Ying, “Multi frequency-band antenna,”, PCT application WO01/91 233, May 2001. [9] M. Martinez-Vazquez and O. Litschke, “Design considerations for quad-band antennas integrated in personal communications devices,” in Proc. Int. Symp. Antennas (JINA), vol. 1, Nice, France, Nov. 2002, pp. 195–198.
