1936 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 51, NO. 8, AUGUST 2003 A Compact Dual-Band Dual-Polarized Patch Antenna for 900/1800-MHz Cellular Systems Tzung-Wern Chiou and Kin-Lu Wong, Senior Member, IEEE Abstract A novel compact design for achieving dual-band dual-polarized radiation suitable for applications in the 900/1800-MHz cellular systems is presented. The proposed antenna consists of a rectangular ring patch (for the 900-MHz operation) and a notched rectangular patch (for the 1800-MHz operation), which are printed on the same layer, and each patch is aperture-coupled by two H-shaped coupling slots to generate two orthogonal linearly polarized waves. By further incorporating a properly designed feed network, the proposed antenna shows good port decoupling of less than 39 db and 34 db for dual linear polarizations in the 900- and 1800-MHz bands, respectively. Details of the antenna design and experimental results are presented. Index Terms Antennas, dual-band antennas, dual-polarized antennas, patch antennas. I. INTRODUCTION PATCH antennas capable of dual-polarized operations are very suitable for applications in modern mobile communication systems to combat the multipath fading problem, which usually causes larger degradation in the system performance [1]. For such applications, a variety of dual-polarized patch antennas have also been reported recently [2] [10] in which good dual-polarized radiation over a wide bandwidth of about 10% or larger and high isolation between the two feeding ports ( less than 30 db) across the entire bandwidth have been achieved. These antennas, however, are mainly designed for single-band operation. Very few designs are reported for dual-band dualpolarized operations for mobile communication systems [11]. For the reported design in [11], the dual-band dual-polarized patch antenna shows a 10-dB return-loss bandwidth covering both the 900-MHz (890 960 MHz, GSM cellular system) and 1800-MHz (1710 1880 MHz, DCS cellular system) frequency bands. Measured isolation less than 32 db in both bands has also been obtained. However, this antenna uses a structure of three stacked patches, and has a total height of about at 900 MHz. In this paper, we propose a new compact dual-band dual-polarized patch antenna suitable for the 900- and 1800-MHz band operations. The proposed antenna has two coplanar radiating patches, one rectangular-ring patch for the 900-MHz operation and one notched rectangular patch placed within the rectangular-ring patch for the 1800-MHz operation, and the total an- Manuscript received December 12, 2000; revised March 21, 2001. T.-W. Chiou was with the Department of Electrical Engineering, National Sun Yat-Sen University, Kaohsiung 804, Taiwan, R.O.C. He is now with Phycomp Taiwan Limited, Kaohsiung 811, Taiwan, R.O.C. K.-L. Wong are with the Department of Electrical Engineering, National Sun Yat-Sen University, Kaohsiung 804, Taiwan. Digital Object Identifier 10.1109/TAP.2003.814728 tenna height is only about at 900 MHz. To feed the antenna, the aperture-coupled feed method is used. Four H-shaped coupling slots are cut in the antenna s ground plane to couple the electromagnetic energy from the feed network to the two radiating patches. To obtain good port decoupling in both of the 900- and 1800-MHz bands, these H-shaped coupling slots are carefully oriented. The feed network is also designed such that the 1800-MHz signal into the radiating patch for the 900-MHz band operation (the rectangular-ring patch) is blocked, so is the case for the 900-MHz signal into the radiating patch for the 1800-MHz band operation (the notched rectangular patch). In this condition, the possible excitation of unwanted modes can be suppressed, and easy impedance matching in both of the 900- and 1800-MHz bands can also be obtained. Details of the proposed antenna are described, and experimental results of the dual-band dual-polarized operation are presented. II. ANTENNA CONFIGURATION AND DESIGN CONSIDERATIONS There are four major parts in the design of the proposed antenna shown in Fig. 1. The first two parts are the dimensions determination of the rectangular-ring patch and notched rectangular patch for the 900- and 1800-MHz operations, respectively. As shown in Fig. 1, the two patches are printed on the same dielectric substrate (patch substrate), and the notched rectangular patch is placed within the rectangular-ring patch to obtain a compact structure. The third part is the arrangement of the coupling slots in the antenna s ground plane [see Fig. 1(c)], and the fourth one is the feed network design [Fig. 1(d)]. The coupling slots and the feed network are printed on two sides of a dielectric substrate (feed substrate). In this study, both the patch and feed substrates used were inexpensive FR4 substrates of thickness 0.8 mm and relative permittivity 4.4. The two substrates are also separated by an air layer of thickness [see Fig. 1; the supporting posts not shown in the figure]. The IE3D simulation software was helpful in obtaining proper parameters of the proposed antenna. The design considerations for the four major parts are described in detail in the following subsection. A. Rectangular-Ring Patch Design for the 900-MHz Band Operation The rectangular-ring patch is designed for achieving the 900-MHz band operation, and is aperture-coupled by using two H-shaped coupling slots [slot 1X and slot 2Y in Fig. 1(c)] for obtaining dual linear polarizations. The two H-shaped slots have a center arm of width 0.5 mm and two side arms of width 1 mm. As for the lengths of the slot s center arm and side arm, owing to the width limitation of the rectangular-ring patch, slot 0018-926X/03$17.00 2003 IEEE
CHIOU AND WONG: COMPACT DUAL-BAND DUAL-POLARIZED PATCH ANTENNA 1937 (c) (d) Fig. 1. Geometry of the proposed dual-band dual-polarized patch antenna; dimensions given in the figure are in millimeters. Side view of the antenna. Patches in layer 1. (c) Coupling slots in layer 2. (d) Microstrip-line feed network. 1X is designed to be narrow (i.e., a relatively shorter center arm and a relatively longer side arm) and slot 2Y is with a wide H shape, having a relatively longer center arm and a relatively shorter side arm. Also, since the coupling-slot size can affect the resonant frequency of the antenna, the dimensions of the rectangular-ring patch in parallel to the and axes are chosen to be different to achieve the same operating frequencies around 900 MHz. The designed patch dimensions are given in Fig. 1. B. Notched Rectangular Patch Design for the 1800-MHz Band Operation A notched rectangular patch is designed for the 1800-MHz band operation, and the designed patch dimensions are also given in Fig. 1. By inserting a pair of slits (length and width 1 mm) along the direction [see Fig. 1], the side length of the notched rectangular patch along the direction can be reduced, which is helpful in obtaining a larger gap between the notched rectangular patch and the rectangular-ring patch to reduce the possible coupling between the two radiating patches. In this study, it is found that a gap of 5 mm is required between the two radiating patches. In this case, very small effects on the measured return loss and port isolation of the proposed antenna are observed. Also, note that since the coupling slots (slot 2X and slot 1Y) are arranged along the direction, no slits are introduced in the notched rectangular patch in the direction to avoid the decreasing in the electromagnetic energy coupling from the feed line to the patch. For this reason, the required side length of the notched rectangular patch in the direction is larger than that in the direction. This also leads to a larger side length of the rectangular-ring patch in the direction than in the direction. C. Coupling Slots Arrangement in the Ground Plane All the H-shaped coupling slots (slots 1X, 1Y, 2X, and 2Y) have the same slot widths (0.5 and 1 mm for the slot s center arm and side arm, respectively), and the lengths of the slots center arms and side arms are given in Fig. 1(c). In order to obtain high port decoupling, slots 1X and 2Y for the 900-MHz band operation are arranged such that the center arm of slot 1X is in the direction of the microstrip feed line of slot 2Y. For slots 1Y and 2X for the 1800-MHz band operation, the same arrangement is applied. In this case, high isolation between ports 1 and 2 is obtained for the proposed antenna. D. Feed Network Design In addition to the coupling-slot arrangement described in part C of this section, the feed network is also designed such that the 1800-MHz (900-MHz) signal into the rectangular-ring patch (notched rectangular patch) is blocked. In this condition, the possible excitation of unwanted modes is suppressed, and easy impedance matching of the proposed antenna in the 900- and 1800-MHz bands is also obtained. To achieve this goal, the microstrip-line feed network shown in Fig. 1(d) is designed. The arrangement of the feed networks for ports 1 and 2 is the same. The characteristic impedance of all the microstrip-line sections in the feed network, except and sections, is chosen to be. The parameters of the microstrip-line sections in
1938 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 51, NO. 8, AUGUST 2003 TABLE I LENGTH AND WIDTHS OF THE MICROSTRIP-LINE p SECTIONS IN THE FEED NETWORK. (= 182:4 mm) IS THE GUIDED WAVELENGTH IN THE FEED SUBSTRATE AT 900 MHz, DETERMINED FROM = " ( IS THE FREE-SPACE WAVELENGTH AND " IS THE EFFECTIVE RELATIVE PERMITTIVITY) Fig. 3. Measured isolation against frequency. Fig. 2. Measured return loss against frequency; ` = 13 mm ground 0 plane size = 150 2 150 mm. Other design dimensions are shown in Fig. 1 and Table I. Port-1 excitation. Port-2 excitation. the feed network are given in Table I. The section has a length of and is placed at a distance of away from point a( denotes the guided wavelength in the feed substrate at 900 MHz). In this case, the impedance at point b seen into the antenna at 900 MHz is zero (short-circuit condition), and thus is infinite (open-circuit condition) at point a. This indicates that the 900-MHz signal into the notched rectangular patch is blocked. Also note that the bandwidth of the single-stub band-stop filter using the above-described microstrip-line section is about 25%, which is larger than the operating bandwidth studied here. On the other hand, since and sections all have a half wavelength at 1800 MHz, no impedance mismatch for the 1800-MHz signal is expected; and thus good excitation of the notched rectangular patch in the 1800-MHz band is still obtained. For the case of the 900-MHz excitation, the blocking of the 1800-MHz signal into the rectangular-ring patch is achieved by the adding of the microstrip-line section with a length of ( is again the guided wavelength in the feed substrate at 900 MHz). However, the section will also affect the 900-MHz signal into the rectangular-ring patch. To solve this problem, the microstrip-line section is added at a distance away from point c. In this case, the 1800-MHz signal into the rectangular-ring patch is still blocked, and the impedance at point c seen into the antenna at 900 MHz can be derived to be where is the impedance at point c seen into the antenna, and and are the characteristic impedance of and sections, respectively;. From (1), it can be found that by choosing and to be 100 and 125, respectively, the impedance has a real value of 62.5. To achieve an (1)
CHIOU AND WONG: COMPACT DUAL-BAND DUAL-POLARIZED PATCH ANTENNA 1939 Fig. 4. Measured radiation patterns in two principal planes. Port 1 at 900 MHz. Port 1 at 1800 MHz. Fig. 5. Measured radiation patterns in two principal planes. Port 2 at 900 MHz. Port 2 at 1800 MHz. impedance very close to 50 for, increasing values of and need to be selected, which quickly decreases the widths of the microstrip-line sections. Since decreasing microstrip-line widths requires more care in the fabrication of the feed network, and in this study are chosen to be 100 and 125, respectively. In this case, the impedance mismatch for the 900-MHz signal is slight, and good measured return loss for the proposed antenna operated in the 900-MHz band is obtained. Also, as shown in Fig. 1(d),,,, and are tuning-stub lengths for slots 1X, 2X, 1Y, and 2Y, respectively. In this design,,,, and are selected to be 7.0, 3.5, 5.5, and 6.5 mm, respectively. It should also be noted that the feed network design described here is not the unique solution for the proposed antenna. However, the present feed network provides good results for the proposed antenna. III. EXPERIMENTAL RESULTS AND DISCUSSION A prototype of the proposed antenna was constructed and studied. Fig. 2 shows the measured return loss for port-1 and port-2 excitation. The total height of the radiating patch to the antenna s ground plane is 13.6 mm, corresponding to about 0.04 free-space wavelength at 900 MHz. The simulated results from the IE3D simulation software are also shown for comparison. Good agreement is observed, and the IE3D simulation software is helpful in the design of the proposed antenna. The obtained 10-dB impedance bandwidths for the 900- and 1800-MHz bands are about 10% and cover the 900-MHz (890 960 MHz, GSM cellular system) and 1800-MHz (1710 1880 MHz, DCS cellular system) frequency bands. The measured and simulated isolation between ports 1 and 2 is also presented in Fig. 3. From the mea-
1940 IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 51, NO. 8, AUGUST 2003 sured results, the isolation across the 900- and 1800-MHz bands is less than 39 and 34 db, respectively. Very good port decoupling is obtained for the proposed antenna. Radiation characteristics of the proposed antenna were also studied. Measured radiation patterns in two principal planes at 900 and 1800 MHz for port-1 and port-2 excitation are plotted in Figs. 4 and 5, respectively. Good broadside radiation patterns are obtained, and the obtained antenna gain is about 6.5 to 7.3 dbi. The estimated antenna efficiency is about 60%. For both the 900- and 1800-MHz band operations, the dual linearly polarized waves excited by ports 1 and 2 are also seen to be with orthogonal polarizations. IV. CONCLUSION A dual-band dual-polarized patch antenna operated in the 900- and 1800-MHz frequency bands with a compact structure has been proposed and experimentally studied. The proposed antenna has impedance bandwidths of about 10% in the 900- and 1800-MHz bands, and shows high isolation between the two feeding ports (less than 39 and 34 db for the 900- and 1800-MHz bands, respectively). If the design can be improved to have a higher return loss (14 db or 1.5:1 VSWR), the proposed antenna would be very suitable for applications in the 900/1800-MHz cellular systems for dual-polarized operations. Also, it is possible for the proposed antenna to have 2 2 ports instead of 2 ports studied here, if preferred. REFERENCES [1] U. Wahlberg, S. Widell, and C. Beckman, The performance of polarization diversity antennas at 1800 MHz, in Proc. IEEE Antennas Propagation Soc. Int. Symp. Dig., 1997, pp. 1368 1371. [2] S. Hienonen, A. Lehto, and A. V. Raisanen, Simple broadband dualpolarized aperture-coupled microstrip antenna, in Proc. IEEE Antennas Propagation Soc. Int. Symp. Dig., 1999, pp. 1228 1231. [3] T. W. Chiou, H. C. Tung, and K. L. Wong, A dual-polarization wideband circular patch antenna with hybrid feeds, Microw. Opt. Technol. Lett., vol. 26, pp. 37 39, 2000. [4] J.-F. Zuercher and P.Ph. Gay-Balmaz, Dual polarized, single- and double-layer strip-slot-foam inverted patch (SSFIP) antennas, Microw. Opt. Technol. Lett., vol. 7, pp. 406 410, 1994. [5] P. Brachat and J. M. Baracco, Printed radiating element with two highly decoupled input ports, Electron. Lett., vol. 31, pp. 245 246, 1995. [6] F. Rostan and W. Wiesbeck, Design considerations for dual polarized aperture-coupled microstrip patch antennas, in Proc. IEEE Antennas Propagation Soc. Int. Symp. Dig., 1995, pp. 2086 2089. [7] J. A. Sanford and A. Tengs, A two substrate dual polarized aperture coupled patch, in Proc. IEEE Antennas Propagation Soc. Int. Symp. Dig., 1996, pp. 1544 1547. [8] M. Yamazaki, E. T. Rahardjo, and M. Haneishi, Construction of a slotcoupled planar antenna for dual polarization, Electron. Lett., vol. 30, pp. 1814 1815, 1994. [9] B. Lindmark, A novel dual polarized aperture coupled patch element with a single layer feed network and high isolation, in Proc. IEEE Antennas Propagation Soc. Int. Symp. Dig., 1997, pp. 2190 2193. [10] I. Nystrom and D. Karlsson, Reduction of back radiation and crosscoupling in dual polarized aperture coupled patch antennas, in Proc. IEEE Antennas Propagation Soc. Int. Symp. Dig., 1997, pp. 2222 2225. [11] B. Lindmark, A dual polarized dual band microstrip antenna for wireless communications, in Proc. IEEE Aerospace Conf., 1998, pp. 333 338. Tzung-Wern Chiou was born in Taipei, Taiwan, R.O.C., in 1971. He received the B.S. degree from National Taipei Institute of Technology, Taipei, Taiwan, R.O.C., in 1993 and the Ph.D. degree in from National Sun Yat-Sen University, Kaohsiung, Taiwan, R.O.C., in 2002, both in electrical engineering. Currently, he is with Phycomp Taiwan Limited, Kaohsiung, Taiwan, Kaohsiung. His current research interests are in antenna theory and design. Dr. Chiou was one of the winners of the Student Paper Competition at the 2000 National Symposium on Telecommunications, Chungli, Taiwan, R.O.C. and received a Graduate Student Scholarship from Phycomp Taiwan Limited in 2001. Kin-Lu Wong (M 91 SM 97) received the B.S. degree from National Taiwan University, Taipei, Taiwan, R.O.C., and the M.S. and Ph.D. degrees from Texas Tech University, Lubbock, in 1981, 1984, and 1986, respectively, all in electrical engineering. From 1986 to 1987, he was a Visiting Scientist at the Max-Planck-Institute for Plasma Physics, Munich, Germany. Since 1987, he has been with the Department of Electrical Engineering, National Sun Yat-Sen University, Kaohsiung, Taiwan, R.O.C., where he became a Professor in 1991 and, from 1994 to 1997, served as Chairman of the Electrical Engineering Department. From 1998 to 1999, he was a Visiting Scholar with the ElectroScience Laboratory, The Ohio State University, Columbus. He has published more than 270 refereed journal papers and numerous conference articles and has graduated 33 Ph.D. students. He also holds more than 50 patents and has many patents pending. He is the author of Design of Nonplanar Microstrip Antennas and Transmission Lines (New York: Wiley, 1999), Compact and Broadband Microstrip Antennas (New York: Wiley, 2002), and Planar Antennas for Wireless Communication (New York: Wiley, 2003). Dr. Wong is a Member of the National Committee of the Republic of China for the International Scientific Radio Union (URSI), Microwave Society of the Republic of China, and Chinese Institute of Electrical Engineers. He received the Outstanding Research Award from the National Science Council of the Republic of China in 1994, 2000, and 2002. He also received the Young Scientist Award from URSI in 1993, the Excellent Young Electrical Engineer Award from Chinese Institute of Electrical Engineers in 1998, the Excellent Textbook Award for Microstrip Antenna Experiment (in Chinese) from the Ministry of Education of the Republic of China in 1998, and the Outstanding Research Award from National Sun Yat-Sen University in 1994 and 2000. In 2001, he also received the ISI Citation Classic Award for a published paper highly cited in the field. He has been on the editorial board of the IEEE TRANSACTIONS ON MICROWAVE THEORY AND TECHNIQUES and Microwave Optical Technology Letters. He has also been on the Board of Directors of the Microwave Society of the Republic of China. He is listed in Who s Who of the Republic of China and Marquis Who s Who in the World.
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