Double-Sided Printed Triangular Bow-Tie Antenna for UWB Communications Ahmed M. Gomaa, Darwish A. E. Mohamed and Mohab A. Mangoud Department of Electronics and Communications Engineering, Arab Academy for Science & Technology and Maritime Transport, B.O.Box 1029, Alexandria, Egypt e-mail: (darwishm@eng.aast.edu) Abstract In this paper a probe fed printed bow-tie antenna with different configurations are designed to achieve a wide impedance bandwidth. A double-sided printed triangular bow-tie antenna with a pair of slits is designed and a wide impedance bandwidth required for Ultra Wide Band (UWB) applications is achieved.the analysis was carried out by using the finite difference time domain method. Index Terms BOW TIE ANTENNA, PRINTED ANTENNA, ULTRA WIDE BAND ANTENNA. I. INTRODUCTION Much attention has been paid to commercial UWB systems, since the federal communications commission FCC permitted the new radio transmission technology in February 2002 [1]. There has been considerable research effort put into UWB radio technology worldwide, however the non digital part of UWB system, i.e., transmitting and receiving antennas, remains particularly challenging topic. Patch antennas are used in wireless communications because of the following features; light weight, low cost and ease of fabrication.as a draw back, it is well known that the bandwidth of the patch antennas is narrow. Thus there are many techniques are used to increase and improve the bandwidth of printed antennas. As a previous work, a probe fed equilateral triangle patch antenna with a pair of slits was designed [2], that operated at resonant frequency 9 GHz with impedance bandwidth of 15 %. In this paper, new designs of one pair and two pairs of wide slits in rectangular patch are presented in the triangular bow-tie design with a probe fed. Also a double-sided printed triangular bow-tie antenna with two slits is proposed in this paper, the analysis of these designs is based on FDTD method by using remcom (XFDTD) commercial package [4]. In section II, different designs and antennas geometries details for the proposed antennas are illustrated. In section III the results will be discussed and a comparison between all proposed antennas is presented. Finally, conclusions and the recommended future work are presented in section IV. II. Antenna Structure And Design Guide Lines A- A Probe Fed Equilateral Triangular Patch Antenna With A Pair of Slits: A probe fed equilateral triangle with a pair of slits is redesigned as shown in figure (1) to operate at the resonance frequency 6.8 GHz to work in the UWB, the design has been accomplished by using the design equations in [5]. The design of the equilateral triangle patch antenna with a pair of slits has been carried out using Duroid 5880 substrate with permittivity εr =2.2 and thickness h=3.148 mm. As a second technique, a double sided printed triangular bow-tie antenna was designed with a microstrip fed line by Katsuki kiminami [3] to operate at resonant frequency 9.1 GHz with impedance bandwidth of 3.4 times.
Figure.1. A Probe Fed Equilateral Triangle Patch Antenna with a pair of slits Figure.3. A Probe Fed Triangular Bow-Tie antenna with a pair of slits B- A Probe Fed Triangular Bow-Tie Antenna with a Pair of Slits: Figure (2) shows an initial design for design of a probe fed triangular bow-tie antenna without slits and figure (3) shows a probe fed triangle bow-tie antenna with a pair of slits. The pair of slits in figure (3) was embedded in one of the two sides of the printed triangular bow-tie antenna with a width of 1 mm and length of 10 mm each. The design has been carried out using Duroid 5880, substrate εr =2.2 with thickness of h=3.148 mm and substrate dimensions of (40 mm x 50 mm),as it is known that, with an inserted slit a dual frequency operation can be obtained [6]. The difference between the two resonances can be controlled by changing the separation between the two slits, where the separation between the slits in this design was adjusted to be 2 mm as shown in figure (4). Figure.4. A Probe Fed Triangular Bow-Tie antenna with a Pair of slits after adjustment C- A Probe Fed Triangular Bow-Tie Antenna with a Two Pair of Slits: In this design, in order to increase the impedance bandwidth an extra pair of slits was embedded on the top side of the bow-tie as shown in figure (5). To reach the best results for uwb applications the width of the slits on the top side of the triangular bow-tie antenna was adjusted to be 2.25 mm, 1mm separation between the two slits and length of 10.75 mm each. While the slits width of the bottom side of the triangular bow-tie antenna was adjusted to be 1.50 mm, 1mm separation between the two slits and length of 10.25 mm each and this adjustment is shown in figure (6). The design has been carried out using Duroid 5880, substrate (εr =2.2) with thickness of (h=3.148 mm)... Figure.2. A Probe Fed Triangular Bow-Tie AntennaWithout slits
Figure.5. A Probe Fed Triangular Bow-Tie antenna with 2 Pair of slits Figure.7. Double-sided printed triangular bow-tie antenna E- Double-Sided Printed Triangular Bow-Tie Antenna with a Pair of Slits: In order to improve the impedance bandwidth of the previous design, a Duroid 5880 substrate εr =2.2 is used of the same height and same side length, a pair of embedded slits of width 4.5 mm, 1.25 mm separation between the slits and length of 12.25 mm each as shown in figure (8). The resultant dimensions of the substrate are 40 mm (x direction) X 37 mm (y direction). Figure.6. A Probe Fed Triangular Bow-Tie antenna with 2 Pair of slits after adjustment D- Double-Sided Printed Triangular Bow-Tie Antenna: A double sided printed triangular bow-tie antenna is designed with a microstrip fed line as was used by Katsuki kiminami [3]. The triangular bow-tie (as shown in figure (7) ) has designed with equal sides of length 22 mm. The design has been carried out using Duroid 5880 substrate εr =2.2 with thickness h = 1.27 mm and the side length of the equilateral triangle was determined by solving the same design equations that were used in the previous designs. A 6.13 % impedance bandwidth is obtained; which is very narrow bandwidth for UWB applications. Figure.8. Double-sided printed triangular bow-tie antenna with a pair of slits
III. FDTD ANALYSIS AND RESULTS The Remcom (XFDTD) package [4] is used in the analysis of the previous designs; the analysis is performed using the finite difference time domain method. Small cell size is used upon a certain calculations in order to reduce the dispersion [7] ( x =0.25, y=0.25, z=0.25) in the x, y and z directions respectively. The time step was also calculated based on the calculated cell size to achieve the accuracy and stability of the results [8].Perfectly matching layer (PML) is used to absorb the reflection from the outer boundary [8]. The Probe Fed Triangular Bow-Tie antenna with a pair of slits shown in figure (1) is simulated, figure (9) shows the variation of S11 Parameters versus frequency and the impedance bandwidth is found to be 18.9 %, figure (15) shows the Gain Pattern of E-Plane for Probe Fed Equilateral Triangular Patch Antenna with a pair of slits at operating frequency 5.7 GHz and 6.7 GHz, the gain is found to be 5dB and Figure (16) shows the Gain Pattern of H-Plane for Probe Fed Equilateral Triangular Patch Antenna with a pair of slits at operating 5.7 GHz and 6.7 GHz, the gain is found to be the same as E-Plane equal to 5dB. A Probe Fed Triangular Bow-Tie Antenna with a Pair of slits is designed as shown in figure (4) and is simulated where it is found that the impedance bandwidth is of about 16.6 % as shown in the S11 parameter curve in figure (10),while figure (11) shows a comparison of S11 parameter between Probe Fed Triangular Bow-Tie Antenna [ a-without Slits, b-with a pair of Standard Slits, c-with Modified 2 Slits ], figure (17) shows the Gain Pattern of E-Plane for Probe Fed Triangular Bow-Tie Antenna with a pair of slits at operating frequency 6.8 GHz and 7.8 GHz, the gain is found to be 5dB. Figure (18) shows the Gain Pattern of H-Plane for Probe Fed Triangular Bow-Tie Antenna with a pair of slits at operating frequency 6.8 GHz and 7.8 GHz, the gain is found to be 3dB. An impedance bandwidth of about 19% is obtained from the simulated Probe Fed Triangular Bow-Tie Antenna with a two Pair of Slits as in figure (6), the S11 parameter curve shows clearly the impedance bandwidth in figure (12), while figure (13) shows a comparison of S11 between Probe Fed Triangular Bow- Tie Antenna [ a-without Slits, b-with a 2 pair of Standard Slits, c-with Modified 4 Slits ], figure (19) shows the Gain Pattern of E-Plane for Probe Fed Triangular Bow-Tie Antenna with a 2 pair of slits at operating frequency 6.8 GHz and 7.8 GHz, the gain is found to be 4dB. Figure (20) shows the Gain Pattern of H-Plane for Probe Fed Triangular Bow-Tie Antenna with a 2 pair of slits at operating frequency 6.8 GHz and 7.8GHz, the gain is found to be less than 0dB which is not as good as the E-Plane pattern. After simulating the Double-Sided Printed Triangular Bow-Tie Antenna shown in figure (8) the determined impedance bandwidth in this design is found to be 26.4% as shown in the S11 parameter curve in figure (14), in the same figure the difference in impedance bandwidth is clearly observed between the Double-sided printed triangular bow-tie antenna without slits and the Double-sided printed triangular bow-tie antenna with a pair of slits, while the Gain Pattern of E-Plane for Double-Sided Printed Triangular Bow-Tie Antenna with a pair of slits at operating frequency 9 GHz and 10 GHz is shown in figure (21), the gain is found to be 5dB,figure (22) shows the Gain Pattern of H-Plane for Double-Sided Printed Triangular Bow-Tie Antenna with a pair of slits at operating frequency 9 GHz and 10 GHz, the gain is found to be 5dB. IV. CONCLUSION This paper presents a triangular bow-tie antenna and a double sided printed triangular bow-tie antenna for UWB communications.the XFDTD simulator is employeed for design simulation.it has been shown that the performance of the presented designs has been enhanced, in which the enhancment is mostly dependent on the adjustment of the embedded slits.it is also observed that the gain pattern are having a good results and the bandwidth for -10dB return loss has been determined for all the designs, where it is found that the best design is the Double-Sided Printed Triangular Bow-Tie Antenna with Two Slits that give an impedance bandwidth of about 21.86 %, which has a surface area of about half the area of the presented Double-Sided Bow-Tie antenna in [6], which makes the design a compact design with a smaller surface area and lower impedance bandwidth. As an extension for the present work, we recommend the following items to be studied and investigated such as using different techniques to improve the bandwidth of the present designs, also new geometries can be presented and improved such as; the diamond shape and rounded diamond instead of the triangular shape.
REFERENCES [1] Fcc 1 st Report and Order on Ultra-Wideband Technology, Feb.2002. [2] Osama Gaafar, Darwish.M.Abdel Aziz, Hadia M.Elhennawy, Wide-Band Equilateral Triangular Slot and Microstrip Antennass,23 rd National Radio Science Conference (NRSC 2006),Paper page B18-1 till B18-11,March (14-16) 2006,El Monofia-Egypt. [3] Katsuki Kiminami,Toshiyuki Shiozawa,Akimasa Hirata, Double-Sided Printed Bow-Tie Antenna For UWB Communications, IEEE Antennas and WIrless Propagation Letters, VOL.3, May.2004. [4] XFDTD.Version 6.0.6.3,Remcom Inc. [5] I.J.Bahl, P.Bhatia Microstrip Antennas Artec House, 1980, Chap.4. [6] K-L Wong Compact and Broadband Microstrip Antennas Newyork, John Wiley and Sons, 2002. [7] Kunz K.S.,Lubbers R.J. The finite difference time Domain for electromagnetism CRC,1993. [8] Allen Taflove Computational Electrodynamics: The Finite Difference Time Domain Method,Artec House,1995,Chap.7 Figure 9: S11 for Probe Fed Equilateral Triangle Patch Antenna with a pair of slits Figure 10: S11 for Probe Fed Triangular Bow-Tie Antenna with a Pair of Slits
Figure 11: Comparison of S11 between Probe Fed Triangular Bow-Tie Antenna [ a-without Slits, b-with a pair of Standard Slits, c-with Modified 2 Slits ] Figure 13: Comparison of S11 between Probe Fed Triangular Bow-Tie Antenna [a-without Slits, b-with a 2 pair of Standard Slits, c-with Modified 4 Slits] Figure 12: S11 for Probe Fed Triangular Bow- Tie Antenna with 2 Pair of Slits Figure 14: Comparison of S11 between DSPTBTA [a-with a pair of slits, b-without slits]
Figure 15: Gain Pattern of E-Plane for Probe Fed Equilateral Triangular Patch Antenna with a pair of slits at 5.7 GHz and 6.7 GHz Figure 17: Gain Pattern of E-Plane for Probe Fed Triangular Bow-Tie Antenna with a pair of slits at 6.8 GHz and 7.8GHz Figure 16: Gain Pattern of H-Plane for Probe Fed Equilateral Triangular Patch Antenna with a pair of slits at 5.7 GHz and 6.7 GHz Figure 18: Gain Pattern of H-Plane for Probe Fed Triangular Bow-Tie Antenna with a pair of slits at 6.8 GHz and 7.8GHz
Figure 19: Gain Pattern of E-Plane for Probe Fed Triangular Bow-Tie Antenna with a 2 pair of slits at 6.8 GHz and 7.8GHz Figure 21: Gain Pattern of E-Plane for Double-Sided Printed Triangular Bow-Tie Antenna with a pair of slits at 9 GHz and 10 GHz Figure 20: Gain Pattern of H-Plane for Probe Fed Triangular Bow-Tie Antenna with a 2 pair of slits at 6.8 GHz and 7.8GHz Figure 22: Gain Pattern of H-Plane for Double-Sided Printed Triangular Bow-Tie Antenna with a pair of slits at 9 GHz and 10 GHz