Wide-Band Modified Printed Bow-Tie Antenna With Single and Dual ...

IEEE TRANSACTIONS ON ANTENNAS AND PROPAGATION, VOL. 53, NO. 9, SEPTEMBER 2005

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Wide-Band Modified Printed Bow-Tie Antenna With Single and Dual Polarization for C– and X-Band Applications Abdelnasser A. Eldek, Member, IEEE, Atef Z. Elsherbeni, Senior Member, IEEE, and Charles E. Smith, Life Senior Member, IEEE

Abstract—A modified printed bow-tie antenna is designed to simultaneously cover the operations in the C and X-bands from 5.5 to 12.5 GHz. The presented antenna has an end fire radiation pattern that makes it suitable for integration in single and dual polarized phased array systems. The antenna exhibits small size and wide bandwidth of 91%. The radiation characteristics are presented for a single element and a linear array of this antenna. Index Terms—Bow-tie, dual polarization, phased arrays, radar, wideband.

I. INTRODUCTION

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RINTED microstrip antennas are widely used in wireless communication and phased array applications. They exhibit a low profile, small size, light weight, low cost, high efficiency, and ease of fabrication and installation. Furthermore, they are readily adaptable to hybrid and monolithic microwave integrated circuits’ fabrication techniques at RF and microwave frequencies [1]. Communication and phased array systems that operate in the C and X-bands are normally designed using separate antennas for each band. Since it is becoming more and more important to use such systems in one setting, it is desirable to design a single antenna that operates in both frequency bands. This, in turn, requires a wideband antenna that covers the two bands. In addition, many applications require end fire patterns, which can be produced by different types of antenna elements. Among the most widely used printed antennas in phased array systems are the quasi-Yagi antenna [2]–[6], dipole antenna [7]–[11], and printed bow-tie antenna [12]–[15]. The quasi-Yagi provides up to 48% bandwidth [2]–[6]. The microstrip-fed dipole provides 2:1 VSWR of 19%, 50%, 56%, and 40% impedance bandwidth in [7]–[9] and [10], respectively, and 1.5:1 VSWR of 30% in [11]. The microstrip fed modified dipole (bow-tie) antennas presented in [12]–[14] provide up to 50% bandwidth. Recently, the authors showed that replacing the dipole and the director of the

Manuscript received September 27, 2004; revised November 24, 2004. A. A. Eldek was with the Center of Applied Electromagnetic Systems Research (CAESR), Department of Electrical Engineering, The University of Mississippi, University, MS 38677 USA. He is now with the Department of Computer Engineering, Jackson State University, Jackson, MS 39217 USA. A. Z. Elsherbeni and C. E. Smith are with the Center of Applied Electromagnetic Systems Research (CAESR), Department of Electrical Engineering, The University of Mississippi, University, MS 38677 USA (e-mail: [email protected]; [email protected]). Digital Object Identifier 10.1109/TAP.2005.851870

quasi-Yagi antenna with a bow-tie for the X-band operations improves the bandwidth (60%), size, and radiation characteristics of the antenna [15]. Further research by the authors resulted in a novel coplanar waveguide fed slot and microstrip fed printed antennas, which are called slot and printed Lotus antennas [16]. , The printed Lotus provides 57% bandwidth relative to and 60% relative to . The presented antennas, however, cannot simultaneously cover the C and X operating bands, which is the objective of this paper. This paper presents a modified printed bow-tie antenna that exhibits a wide bandwidth (BW). The return loss, and far field radiation characteristics of this antenna are presented. In addition, two array configurations are presented to improve the pattern stability across the operating bandwidth. The simulation and analysis for the presented antennas are performed using the commercial computer software package, Ansoft HFSS, which is based on the finite element method. Measurements of return loss, and radiation patterns are also conducted for verification of these new antenna designs. II. SINGLE ELEMENT MODIFIED BOW-TIE The proposed antenna is printed on a Rogers RT/Duroid 6010/6010 LM substrate of a dielectric constant of 10.2, a of 0.0023 and a thickness of 50 mil (1.27 conductor loss mm). The geometry, parameters, and top and bottom views for a prototype of the proposed antenna are shown in Fig. 1. The antenna consists of two identical printed bows, one on the top and one on the bottom of the substrate material. The top and bottom bows are connected to the microstrip feedline and the ground plane through a stub and mitered transition to match the bow-tie with the 50 feedline, as illustrated in Fig. 1. The antenna dimensional parameters, shown in Fig. 1, Wf, W1, W2, W3, W4, W5, Lf, L1, L3, L3. L4, L5, L6, and L7 are 1.2, 1.52, 0.45, 0.62, 2, 2.49, 10, 5.34, 0.45, 0.68, 0.24, 2.61, 5.56, and 9.68 mm, respectively. The substrate size (width length) is . (30 29) The return loss is computed using Ansoft HFSS and measured using a 8510 vector network analyzer and is shown in Fig. 2. The small discrepancies between the computed and measured results may occur because of the effect of the SMA connector and fabrication imperfections. Both the simulation and measurements show that the antenna operates over a wide range that extends from 5.3 GHz to more than 14.2 GHz, with an impedance bandwidth of approximately 91%.

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Fig. 1.


Antenna geometry, parameters, and prototype.

Fig. 3. Comparison between the measured and computed radiation patterns in the (a) E-plane and (b) H-plane, for the modified bow-tie antenna at 9 GHz. Fig. 2. Measured and computed return loss for the modified bow-tie antenna.

Compared to the conventional bow-tie antenna, this antenna has a much wider bandwidth, which may result from two properties of this new design. First, it has a wide rectangular part that decreases the reflections from the sudden truncation of the triangular bow-tie shape. Second, it has a well-designed matching circuit that matches the bow-tie with the microstrip feed line. The measured and computed radiation patterns at the operating band center frequency, 9 GHz, are shown in Fig. 3. A good agreement is noticed, which further verifies the simulation results using Ansoft HFSS. The radiation patterns are then computed at selective frequencies that cover almost the entire operating band, and shown in Fig. 4 at 6, 8, 10, and 12 GHz. The properties of these patterns are summarized in Table I. Good radiation characteristics are obtained up to 10 GHz. The radiation pattern starts to deteriorate at 12 GHz. For the frequencies less than 12 GHz, the antenna has wide beamwidth that ranges from 95 to 150 in the E-plane and from 115 to 180 in the H-plane. It has a maximum cross polarization level of and in the E and H planes, respectively, and a minimum front to back ratio (F-to-B) of 12 dB. The antenna gain has an average value of 6 dB. According to these results, the operating bandwidth

of the antenna, as a single element, is between 5.3 and 10 GHz, which is around 61.4%. However, unconventional configuration of this antenna can further improve the radiation characteristics at higher frequencies in array environments. III. TWO-ELEMENT ARRAYS The coupling between array elements is an important parameter in phased array performance, because high coupling results in scan blindness and anomalies within the desired bandwidth and scan volume. Therefore, a two-element array is designed to examine the coupling between elements. In addition, another configuration of two-element array is designed to improve the pattern stability above 10 GHz. The two configurations are shown in Fig. 5. Array 1 consists of two identical elements, while the second element in Array 2 is mirrored along the y-axis, and consequently a 180 phase shift is introduced at port 2 in order to force the surface currents in the two elements to be in the same direction. This modification in Array 2 provides balanced patterns at high frequencies, where the effect of the substrate height is significant. In order to reduce the grating lobes at high frequencies, the distance between elements

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Fig. 6. Array 1. (a) Prototype. (b) Measured and computed S21.

Fig. 4. Computed radiation patterns at 6, 8, 10, and 12 GHz.

TABLE I FAR FIELD RADIATION PROPERTIES

Fig. 5. Two-element array configurations. (a) Array 1. (b) Array 2.

is chosen to be 14 mm, which is around at the upper frequency of the X-band. Array 1 is fabricated, and its measured and computed S21 are shown in Fig. 6. The average coupling is around in the entire operating band. A comparison between the two arrays is performed in terms of S-parameters as shown Fig. 7, and radiation patterns at 6, 8, 10, 12, and 14 GHz as shown in Fig. 8. S11 and S22 of Array 2 are identical because of the array symmetry. While no significant difference is noticed in the return losses and coupling, notable improvement in the radiation patterns is obtained by using Array 2. These improvements include much

Fig. 7. Computed (a) return loss. (b) Coupling, for Array 1 and Array 2.

lower cross polarization levels, wider beamwidth, symmetrical patterns around the y-axis, and wider usable bandwidth that includes 14 GHz. Hence, Array 2 is expected to perform better as an element in a large phased array system. Two four-element arrays of the modified bow-tie antenna are fabricated (based on Array 2 configuration shown in Fig. 5), with feeding networks for 0 and 10 steering angles. The measurement of the radiation pattern from these two array configurations are presented in the Fig. 9 along with the HFSS simulation results at 9 GHz. A 180 phase shift is introduced by increasing the length of the feedlines of the second and , where . In order to fourth elements by steer the main beam from 90 to 80 , progressive phase shift, , is added by increasing the feed length by 0, 0.8, 1.6, and 2.4 mm for the elements counted from left to right 1, 2, 3, and 4, respectively. Good agreement is obtained between simulation and measurement results for the designed scanning feature.

IV. DUAL–POLARIZED ARRAYS Dual-polarized arrays are important for many communication systems, especially in wireless remote sensing and mine detection applications. They have the advantage of polarization diversity, which allows the system to transmit and receive multiple and/or arbitrary polarizations. Therefore, dual-polarized arrays of the modified printed bow-tie antenna are designed and their results are presented in this section.

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Fig. 9. Prototypes and results of four-element arrays based on Array 2 configuration. (a) Top view for the array of = 90 . (b) Top view for the array of = 80 . (c) Back view for the two arrays. (d) Measured and computed radiation patterns for the = 90 array. (e) Measured and computed radiation patterns for the = 80 array.

Fig. 10. Configurations for dual polarization antennas. (a) Configuration 1. (b) Configuration 2.

Fig. 8. Comparison between the computed radiation patterns for Array 1 and Array 2 at (a) 6. (b) 8. (c) 10. (d) 12. (e) 14 GHz.

Two geometries for dual polarization based on Array 1 and Array 2, described as configuration 1 and configuration 2,

Fig. 11. Computed return losses and couplings for configuration 1 and configuration 2 of dual polarized array geometries. (a) Return losses. (b) S21. (c) S31. (d) S41.

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presented in Fig. 12, at 6, 8, 10, and 12 GHz. As shown in Fig. 12, the radiation patterns of configuration 1 deteriorate at 10 and 12 GHz, while configuration 2 has lower cross polarization levels, wider beamwidth, symmetrical patterns around the y-axis, and wider usable bandwidth that includes 12 GHz. Therefore, configuration 2 is a better candidate for wideband dual polarized phased array systems. V. CONCLUSION A wideband modified printed bow-tie antenna is designed for C and X-band operations. The modified bow-tie antenna provides 91% impedance bandwidth that covers the entire C and X bands and part of the Ku band. The single element antenna provides wide beamwidth(morethan95 ),lowcrosspolarizationlevel(lessthan ), and relatively high gain in the frequency range between 5.3 and 10 GHz. Furthermore, it produces an endfire radiation patterns with a good front-to-back ratio that exceeds 12 dB. A stable radiation pattern and wide usable bandwidth are obtained using two-elementarraysbyrotatingthesecondelementby180 andintroducing 180 phase shift in its excitation. The antenna is a good candidate for wideband phased array systems with single linear, dual linear or circular polarization. REFERENCES

Fig. 12. Comparison between the computed radiation patterns for configuration 1 and configuration 2 dual polarized arrays with horizontal ports excited at (a) 6 GHz. (b) 8 GHz. (c) 10 GHz. (d) 12 GHz.

arenumbered 1 and 2, while the vertical ports are numbered 3 and 4. shown in Fig. 10, with a 14-mm separation distance between elements. Each configuration consists of four printed modified bow-tie antennas. The horizontal ports are Fig. 11 shows a comparison between the return losses and couplings for configuration 1 and configuration 2. No significant difference is noticed in the return losses and couplings. Both configurations of these antennas operate between 5.5 and 13.5 GHz, and the highest average coupling is around . The radiation patterns when ports 1 and 2 (horizontal ports) are excited are

[1] L. G. Maloratsky, “Reviewing the basics of microstrip lines,” Microw. RF, pp. 79–88, Mar. 2000. [2] Y. Qian, W. R. Deal, N. Kaneda, and T. Itoh, “Microstrip-fed quasi-Yagi antenna with broadband characteristics,” Electron. Lett., vol. 34, no. 23, pp. 2194–2196, 1998. [3] N. Kaneda, Y. Qian, and T. Itoh, “A broad-band microstrip-to-waveguide transition using quasi-Yagi antenna,” IEEE Trans. Microw. Theory Tech., vol. 47, no. 12, pp. 2562–2567, Dec. 1999. [4] W. Deal, N. Kaneda, J. Sor, Y. Qian, and T. Itoh, “A new quasi-Yagi antenna for planar active antenna arrays,” IEEE Trans. Microw. Theory Tech., vol. 48, no. 6, pp. 910–918, Jun. 2000. [5] K. M. K. H. Leong, Y. Qian, and T. Itoh, “Surface wave enhanced broadband planar antenna for wireless applications,” IEEE Microw. Wireless Comp. Lett., vol. 11, no. 6, pp. 62–64, Feb. 2001. [6] N. Kaneda, W. Deal, Y. Qian, R. Waterhouse, and T. Itoh, “A broad-band planar quasi-Yagi antenna,” IEEE Trans. Antennas Propag., vol. 50, no. 8, pp. 1158–1160, Aug. 2002. [7] G.-Y. Chen and J.-S. Sun, “A printed dipole antenna with microstrip tapered balun,” Microw. Opt. Tech. Lett., vol. 40, no. 4, pp. 344–346, Feb. 2004. [8] I. E. Timefeev, J. W. Kim, and G. A. Evtioushkine, “Wideband microstrip array antenna with sidelobe cancellation channels,” Electron. Lett., vol. 34, no. 6, pp. 505–506, 1998. [9] G. A. Evtioushkine, J. W. Kim, and K. S. Han, “Very wideband printed dipole antenna array,” Electron. Lett., vol. 34, no. 24, pp. 2292–2293, 1998. [10] G. Zheng, A. A. Kishk, A. B. Yakovlev, and A. W. Glisson, “Simplified feed for a modified printed Yagi antenna,” Electron. Lett., vol. 40, no. 8, pp. 464–465, Apr. 2004. [11] F. Tefiku and C. A. Grimes, “Design of broad-band and dual-band antennas comprised of series-fed printed-strip dipole pairs,” IEEE Trans. Antennas Propag., vol. 48, no. 6, pp. 895–900, Jun. 2000. [12] S. Deay, C. K. Aanandan, P. Mohanan, and K. G. Nair, “Analysis of cavity backed printed dipoles,” Electron. Lett., vol. 30, no. 30, pp. 173–174, 1994. [13] Y.-D. Lin and S.-N. Tsai, “Analysis and design of broadband-coupled striplines-fed bow-tie antennas,” IEEE Trans. Antennas Propag., vol. 46, no. 3, pp. 459–560, Mar. 1998. [14] G. Zheng, A. A. Kishk, A. B. Yakovlev, and A. W. Glisson, “A broad band printed bow-tie antenna with a simplified feed,” in Antennas Propag. Soc. Int. Symp., vol. IV, Monterey, CA, Jun. 2004, pp. 4024–4027. [15] A. A. Eldek, A. Z. Elsherbeni, and C. E. Smith, “Characteristics of microstrip fed printed bow-tie antenna,” Microwave Opt. Tech. Lett, vol. 43, no. 2, Oct. 2004. [16] A. Z. Elsherbeni, A. A. Eldek, and C. E. Smith, “Wideband slot and printed antennas,” in Encyclopedia of RF and Microwave Engineering, K. Change, Ed. New York: Wiley, 2005.

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Abdelnasser A. Eldek (M’00) received the B.Sc. degree (with honors) in electronics and communications engineering from Zagazig University, Zagazig, Egypt, in 1993, the M.S. degree in electrical engineering from Eindhoven University of Technology, Eindhoven, The Netherlands, in 1999, with the cooperation of Philips Center for Technology and Fontys University for Professional Education (from 1997 to 1999), and the Ph.D. degree in electrical engineering from The University of Mississippi, Oxford, in 2004. He was a Research Assistant with the Department of Microwave, Electronic Research Institute, Cairo, Egypt, from 1995 to 1996. From January 2001 to December 2004, he was a Research and Teacher Assistant with the Department of Electrical Engineering, University of Mississippi. He is currently an Assistant Professor with the Department of Computer Engineering, Jackson State University, Jackson, MS. His current research interests include electromagnetic theory, finite difference time domain method, antenna design, and phased arrays. Dr. Eldek is a Member of the IEEE Antennas and Propagation Society, Mississippi Academy of Science and Sigma Xi, the honor society of research. Atef Z. Elsherbeni (S’84–M’86–SM’91) received the honor B.Sc. degree (with honors) in electronics and communications, the B.Sc. degree (with honors) in applied physics, and the M.Eng. degree in electrical engineering, all from Cairo University, Cairo, Egypt, in 1976, 1979, and 1982, respectively, and the Ph.D. degree in electrical engineering from Manitoba University, Winnipeg, Manitoba, Canada, in 1987. He was a Research Assistant with the Faculty of Engineering at Cairo University from 1976 to 1982, and from 1983 to 1986 at the Electrical Engineering Department, Manitoba University. He was a part time Software and System Design Engineer from March 1980 to December 1982 at the Automated Data System Center, Cairo, Egypt. From January to August 1987, he was a Postdoctoral Fellow at Manitoba University. He joined the faculty at the University of Mississippi in August 1987 as an Assistant Professor of electrical engineering and advanced to the rank of Associate Professor on July 1991, to Professor on July 1997 and is currently the Chair of the Engineering and Physics Division of the Mississippi Academy of Science. He spent a sabbatical term in 1996 at the Electrical Engineering Department, University of California at Los Angeles (UCLA). He has published 65 technical journal articles and 12 book chapters on applied electromagnetics, antenna design, and microwave subjects, and contributed to 210 professional presentations. He is the coauthor of the book MATLAB Simulations for Radar Systems Design (Boca Raton, FL: CRC Press, 2003) and author of the chapters “Handheld Antennas” and “The Finite Difference Time Domain Technique for Microstrip Antennas” in Handbook of Antennas in Wireless Communications (Boca Raton, FL: CRC Press, 2001). He has conducted research in several areas such as: scattering and diffraction by dielectric and metal objects, inverse scattering, finite difference time domain analysis of passive and active microwave devices, field visualization and software development for EM education, dielectric resonators, interactions of electromagnetic waves with human body, and development of sensors for soil moisture and for monitoring of airports noise levels, reflector antennas and antenna arrays, and analysis and design of printed antennas for wireless communications and for radars and personal communication systems. His recent research has been on the application of numerical techniques to microstrip and planar transmission lines, antenna measurements, and antenna design for radar and personal communication systems. Dr. Elsherbeni has honorary memberships in the Electromagnetics Academy and the Scientific Sigma Xi Society. He received the 1996 Outstanding Engineering Educator of the IEEE Memphis Section, the 2001 Researcher/Scholar of the year award in the Department of Electrical Engineering, The University of Mississippi, the 2001 Applied Computational Electromagnetic Society (ACES) Exemplary Service Award for leadership and contributions as Electronic Publishing managing Editor 1999–2001, the 2002 IEEE Region 3 Outstanding Engineering Educator Award, the 2002 School of Engineering Outstanding Engineering Faculty Member of the Year Award, and The Mississippi Academy of Science 2003 Outstanding Contribution to Science Award. He is the past Chair of the Educational Activity Committee for the IEEE Region 3 Section. He is the Editor-in-Chief for the Applied Computational Electromagnetic Society (ACES) Journal, an Associate Editor to the Radio Science Journal, and the electronic publishing Managing Editor of ACES. He serves on the editorial board of the Book Series on Progress in Electromagnetic Research, the Electromagnetic Waves and Applications Journal, and the Computer Applications in Engineering Education Journal.

Charles E. Smith (M’59–LM’86–LSM’97) was born in Clayton, AL, on June 8, 1934. He received the B.E.E., M.S., and Ph.D. degrees from Auburn University, Auburn, AL, in 1959, 1963, and 1968, respectively. While pursuing his advanced degrees from 1959 to 1968, he was employed as a Research Assistant with Auburn University Research Foundation. In 1968, he was an Assistant Professor of Electrical Engineering with The University of Mississippi, University, and became an Associate Professor in 1969. He was appointed Chairman of the Department of Electrical Engineering in 1975, and is currently Professor and Chair Emeritus of this department. He has directed and is heavily involved in the development of The University’s current circuits, electronics, HF and microwave, computer-aided design, and digital systems courses and laboratories. His main areas of interest are related to the application of electromagnetic theory to microwave circuits, antennas, measurements, RF and wireless systems, radar, digital and analog electronics, and computer-aided design. His recent research has been on the application of numerical techniques to microstrip transmission lines, antenna measurements in lossy media, measurement of electrical properties of materials, CAD in microwave circuits, radar designing, and data acquisition using network analyzers. He has published widely in these areas and has more than 200 total publications including journal papers, technical reports, book chapters, and paper presentations. Dr. Smith has advised, or coadvised, 46 M.S. thesis and Ph.D. dissertations, and has received six awards for outstanding teaching and scholarship at The University of Mississippi. He is a member of the IEEE Antennas and Propagation Society, IEEE Microwave Theory and Techniques Society, IEEE Education Society, American Society of Engineering Education, Phi Kappa Phi, Eta Kappa Nu, Tau Beta Pi, and Sigma Xi.