Wideband Rectangular Slot Antenna For Personal Wireless Communication Systems

Transcription

1 Naftall (Tuli) Herscovicl AnTeg 52 Agnes Drive Framlngham, MA USA t1 (508) t 1 (508) (Fax) tuil@leee.org ( ) Chrlstos Chrlstodoulou Department of Electrical and Computer Engineerlng Unlversity of New Mexico Albuquerque, NM USA t 1 (505) (505) (Fax) christos@eece.unm.edu (e-mall) Wideband Rectangular Slot Antenna For Personal Wireless Communication Systems Abdelnasser A. Eldek, Atef Z. Elsherbeni, Charles E. Smith, and Kai-Fong Lee Electrical Engineering Department, The University of Mississippi University, MS USA Tel: +I (662) ; Fax: +I (662) ; elsherbeni@ieee.org Abstract Antenna designs were achieved for wideband operation by the use of a coplanar patch-slot antenna, fed by a coplanar waveguide. This design is easily tuned to operate at 2.45 and 5.75 GHz, with wide bandwidth for wireless systems. The operating frequency is controlled by modifying the patch dimensions. The return loss, input impedance, radiation pattern, directivity, gain, and efficiency of the proposed designs are computed and presented. A parametric study of the antenna is also introduced. Keywords: Wideband antennas; coplanar waveguides; slot antennas; microstrip antennas; wireless LAN 1. Introduction n present-day personal-communication devices, the need for I antennas of small size and high efficiency has generated much attention to the study of compact microstrip antennas. These antennas exhibit low-profile and lightweight properties, as well as low cross-polarization radiation in some designs. However, microstrip antennas inherently have narrow bandwidths and, in general, are half-wavelength structures, operating at the TM,, or TM,, fundamental resonant mode [ 11. In this study, coplanar-patch antennas (CPAs) have been designed with improved bandwidth and size reduction for communication systems. Researchers have made efforts to overcome the problem of narrow bandwidth in coplanar-patch antennas, and various configurations have been presented to extend the bandwidth (BW). Adding a short on the upper slot of the coplanar-patch antenna and varying its length achieved 30% to 40% bandwidth [2] at higher 146 frequencies, for radar applications. Moreover, other researchers investigated the design of a dual-frequency slot antenna, fed by coplanar waveguide (CPW), as reported in [3]. In this paper, a simple design of a coplanar-patch antenna is introduced that achieves high efficiency and reasonable bandwidth, and can easily be tuned to work at different frequency bands. The secondresonance frequencies for these antennas are also presented, to show their ability to work at two frequencies. 2. Antenna Analysis and Results The geometry of the coplanar-patch antenna and its parameters are shown in Figure 1. The antenna consists of a rectangular patch, surrounded by a non-uniform-width slot. As shown in Figure 1, W represents the patch width, L is the patch length, and SI, S2, and S3 are the widths of the upper slot, the left-right slot, and the lower slot, respectively. S4 and S5 are the gap width and feed- / Antenna s and Propagation Magazine, Vol. 44, No. 5, October 2002

2 Figure 5a. The radiation pattern in the xz plane of Design 1 at 5.75 GHz Figure 5b. The radiation pattern in the yz plane of Design 1 at Figure 5c. The radiation pattern in the xy plane of Design 1 at 5.75 GHz GHz. Figure 5d. The three-dimensional radiation pattern of Design 1 at 5.75 GHz. / Antenna s and Propagation Magazine, Vol. 44, No. 5, October

3 line width of the coplanar waveguide, and Lcpw represents the length of the coplanar waveguide. In addition to these parameters, h is the height of the substrate, and E, is the substrate dielectric constant. The dielectric material is RT/duriod 5880, with E, = 2.2. Two antennas were designed for each band of the wireless local-area networks (WLANs): GHz and GHz [4]. Designs 1 and 2 operate at a center frequency (f,) of 5.75 GHz, while Designs 3 and 4 operate at f, = 2.4GHz. A dielectric superstrate of the same thickness as the substrate is included in the antennas labeled Dcsigns 2 and 4. The dimensions of these antennas are listed in Table 1. Figure 1. The geometry and parameters for a coplanar-patch antenna. II-ADS -40 I I I I f(g HZ) Figure 2. A comparison between the return-loss results of ADS Momentum and the FDTD method. Table 1. The dimensions of the coplanar-patch antennas in mm. I Design4 I 44.0 I 9 I 3 I 1.5 I 2 I I 3.17 I The analysis was performed using the commercial computer software package Momentum from Agilent Technologies' advanced design system (ADS), which is based on the Method of Moments (MOM) technique for layered media. The ADS simulator, Momentum, solves mixed-potential integral equations (MPIE), using full-wave Green's functions. A verification of our simulation procedure was confirmed by comparing the numerical results of a coplanar-patch antenna's return loss from an FDTD computation with that of ADS Momentum. This comparison revealed good agreement, as shown in Figure2 for a simulated antenna with W=23mm, L=4mm, Lcpw=3Smm, Sl=lmm, S2=Imm, S3 = I mm,s4 = 0.5 mm, S5 = 3.5mm, h = mm, and &. = 2.2. The first parameter under study was Lcpw. For the designs in Table 1, Lcpw was set at 3.5 mm. By increasing Lcpw, it was found that the resonance frequency decreases, but returns back at certain lengths for all designs presented. It is known that the input impedance for a coplanar waveguide structure is given by Z + 'Z tanpl 2, =z, O Z, + jzl tanpl At 1 = /2,/2, Z, = Z,, From that numerical experiment Ag can be defined, and then E,., Ag =- 4 G Table 2 shows 4,,Ig, and can be calculated from for all of the coplanar-patch antenna designs listed in Table 1. As shown in Table 2, increasing the substrate height increases slightly, as seen by comparing Designs 1 and 3, and Designs 2 and 4. Although the superstrate increases and decreases the overall size of the antenna, as shown in Tables 2 and 1, it decreases the bandwidth and the radiation efficiency (7). Table 3 shows the center frequency (f,), the Table 2. 4, /2,, and E.S~ for the coplanar-patch antenna designs. ' ~ g I Crg I Erefkr I 70.0% 95.6% 71.0% Table 3. f,, bandwidth (BW), D, and 7 for the coplanar-patch antenna designs. Design 1 Design 2 Design 3 Design % % % % % % % % 148 / E Antenna's and Propagation Magazine, Vol. 44, No. 5, October 2002

4 X-Z I 80 Figure 8a. The radiation pattern in the xz plane of Design 2 at 5.75GHz. 180 Figure 8b. The radiation pattern in the yz plane of Design 2 at 5.75 GHz. Figure 8c. The three-dimensional radiation pattern of Design 2 at 5.75 GHz. Figure 9. The return loss of Design 3. / Antenna s and Propagation Magazine, Vol. 44, No. 5, October

5 %) Table 4. The dimensions of the coplanar-patch antennas in terms of Ag. Design I 0.54 I I 1.40 Design I 0.53 I I 1.47 Table 5. The second-resonance frequency ( fc2) and bandwidth (BW), D, and r at these frequencies. Table 6. The properties of Designs 3 and 4 and the antenna of [3] at the first and second resonance frequencies. Table 7. The properties of the coplanar-patch antennas at selected frequencies covering the entire band. I Design 1 I Frequency (GHz) 5.17 D (db) 2.72 G (db) (%) bandwidth, the directivity (D), and 7 for all of the coplanar-patch antenna designs. By observing the influence of various parameters on the antenna performance, it was found that the dominant factors in coplanar-patch antenna design for WLAN applications are the patch width in terms of Ag and the total length of the slot (Ltotul). Ltotal is the total centerline length of the slot, defined as Dotal= 2(w + L + Lcpw + s2) + s1+ $3 - S4 -s5. (3) By studying the given designs, it was clear that F' was about 0.5Ag, and that the total length was about 1Xg. At the same time, the patch length in all designs was about O.lAg, as shown in Table 4. In general, Ltotal controls the resonant frequency, while the patch dimensions and slot widths control the level of the return loss and bandwidth. Further study revealed that the resonant frequency decreases when increasing h, E,,, W, L, S1, S2, and S4, and by decreasing S3 and S5. Increasing S1 decreases the return loss, especially at the center of the band, such that S1 may have variable width with a maximum at the center. Increasing h causes to increase and Ag to decrease, thus increasing Ltotal in terms of Ag and decreasing f,. Similar observations were noted while increasing E,, All other parameters decrease f,, due to the increase of Ltotul, except for S3, which may contribute with Lcpw to matching the source impedance. Although the effect of all of these parameters is clear on fc, it is not clear which one parameter can primarily increase the bandwidth. Table 5 shows the second-resonance frequencies ( fc2), and the bandwidth, D, and 77 at these frequencies. The secondresonance frequency is about 2 f,. The efficiency is less than that at f, by about 20%, and the antennas are more directive at fc2 than at f,. In [3], an antenna with a rectangular slot and a rectangular slot loop-fed with a coplanar waveguide were designed to work at (GHz) I I 2.64 I ~ [\ ' 3-9 v 7-30 //I......,....-i l \ / i... i..., f(ghz) Figure 3. The return loss of Design / Antenna's and Propagation Magazine, Vol. 44, No. 5, October 2002

6 x-z 180 Figure lla. The radiation pattern in the xz plane of Design 3 at 2.45 GHz. X-Y Figure llb. The radiation pattern in the yz plane of Design 3 at Figure llc. The radiation pattern in the xy plane of Design 3 at 2.45 GHz GHz. Figure lld. The three-dimensional radiation pattern of Design 3 at 2.45 GHz. / Antenna s and Propagation Magazine, Vol. 44, No. 5, October

7 / real Zin --- imag Zin I oc imag Zin r , f(ghz) f(ghz) Figure 4. The input impedance of Design 1. Figure 10. The input impedance of Design 3. - If I I f(g HZI Figure 6. The return loss of Design 2. Figure 12. The return loss of Design 4. J - real Zin --- imag Zin /*- - :,*/ * i...*.?k...;-... S ; c.a I */- i;j -50,*+ /*- ; oo5 152 I 5'5 f(ghz) I Figure 7. The input impedance of Design 2. I I I I ?(GHzf Figure 13. The input impedance of Design 4. / Antenna's and Propagation Magazine, Vol. 44, No. 5, October 2002

8 X-Z The radiation pattern in the xz plane of Design 4 at I c 180 Figure 14b. The radiation pattern in theyz plane of Design 4 at 2.45 GHz. Figure 14c. The 4 at 2.45 GHz. three-dimensional radiation pattern of / E Antenna s and Propagation Magazine, Vol. 44, No. 5, October

9 two frequencies. Table 6 gives a comparison between this antenna 3. Jin-Sen Chen, Dual-Frequency Slot Antennas fed by and the third and fourth designs. It can be seen that the antenna of Capacitively Coplanar Waveguide, Microwave and Optical Tech- [3] has lower bandwidth and higher gain at f,, and higher band- nology Letters, 32, 6, March 20, 2002, pp width and lower gain at fez, The efficiency of this antenna is not given. The coplanar-patch antennas with the dimensions in Table 1 were designed to operate at f, = 5.75 GHz and 2.45 GHz. The return loss of Design 1 is shown in Figure 3, while Figure 4 shows the corresponding input impedance as real and imaginary parts. Figure 5 shows the radiation patterns at f, = 5.75 GHz in the xz, yz, and xy planes, along with the corresponding three-dimensional pattern of the total field. The return loss of Design 2 is shown in Figure 6, while Figure 7 shows the corresponding input impedance as real and imaginary parts. Figure 8 shows the radiation patterns at f, = 5.75 GHz in the xz and yz planes, and the three-dimensional pattern. There is no radiation in the xy plane. The return loss of Design 3 is shown in Figure 9, while Figure 10 shows the corresponding input impedance as real and imaginary parts. 4. D. M. Pozar, Microwave and RF Design of Wireless Systems, New York, NY, John Wiley and Sons, 2001, p. 4. Introducing the Authors Figure 11 shows the radiation patterns at f, = 2.45 GHz in the xz, yz, and xy planes, in addition to the three-dimensional pattern. The return loss of Design 4 is shown in Figure 12, while Figure 13 shows the corresponding input impedance as real and imaginary parts. Figure 14 shows the radiation patterns at f, = 2.45 GHz in the xz and yz planes, and the three-dimensional pattern. There is no radiation in the xy plane. Table 6 shows the stability of each design over the entire band by showing its properties at four different frequencies. It is clear that all designs have similar properties in the entire band. They achieve good 7, with bandwidth ranges from 15.5% to 22.2%, and low directivity, which is required in wireless local-area communication applications. The designs with superstrate material, simulating a practical implementation, decrease the antenna size, and slightly reduce the bandwidth and 7. These designs have symmetric radiation patterns in the xz and yz planes, and zero fields in the xy plane. Abdelnasser Eldek received an honor BSC degree in Electronics and Communications Engineering from Zagazig University, Zagazig, Egypt, in 1993, and an MS degree in Electrical Engineering from Eindhoven University of Technology, Eindhoven, the Netherlands, in He was a Research Assistant with the Electronic Research Institute, in Cairo, Egypt, from 1995 to From 1997 to 1999, he was a masters student at Eindhoven University of Technology, with the cooperation of the Philips Center for Technology and Fontys University for Professional Education, Eindhoven. From 1999 to 2000, he was Assistant Teacher in the Industrial Education College, Beni Suif, Egypt. He is currently working towards his PhD degree and is a Research Assistant in the Department of Electrical Engineering at the University of Mississippi. 3. Conclusion Four designs of coplanar-patch antennas were presented, for operation at 2.45 GHz and 5.75 GHz. These antennas show high efficiency, low directivity, reasonable bandwidth, and almost constant radiation properties over the entire operating band. The effects of the geometrical and electrical parameters have been studied and reported, to aid the design of these types of antennas. The antennas can work at a frequency equal to twice the intended frequency of operation, but with lower bandwidth and efficiency. 4. References I. K-L Wong, Compact and Broadband Microstrip Antennas, New York, NY, John Wiley and Sons, A. Z. Elsherbeni, Abdelnasser A. Eldek, B. N. Baker, C. E. Smith, and K-F Lee, Wideband Coplanar Patch-Slot Antennas for Radar Applications, 2002 IEEE International Symposium on Antennas and Propagation Digest, San Antonio, TX, June 2002, pp Atef Z. Elsherbeni received an honor BSc degree in Electronics and Communications, an honor BSc degree in Applied Physics, and an MEng degree in Electrical Engineering, all from Cairo University, Cairo, Egypt, in 1976, 1979, and 1982, respectively. He received a PhD degree in Electrical Engineering from Manitoba University, Winnipeg, Manitoba, Canada, in 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 Post-Doctoral Fellow at Manitoba University. Dr. Elsherbeni joined the faculty at the University of Mississippi in August, 1987, as an Assistant Professor of Electrical Engineering. He advanced to the rank of Associate Professor in July, 1991, and to the rank of Professor 154 / E Antenna s and Propagation Magazine, Vol. 44, No. 5, October 2002

10 in July, He spent his first sabbatical term in 1996 at the Electrical Engineering Department, University of California at Los Angeles (UCLA). Dr. Elsherbeni received the 2002 IEEE Region 3 Outstanding Engineering Educator Award; the 2002 School of Engineering Outstanding Engineering Faculty Member of the Year Award; the 2001 Applied Computational Electromagnetic Society (ACES) Exemplary Service Award for leadership and contributions as Electronic Publishing Managing Editor ; the 2001 ResearcheriScholar of the Year award in the Department of Electrical Engineering, the University of Mississippi; and the 1996 Outstanding Engineering Educator of the IEEE Memphis Section. His professional interests include scattering and diffraction of electromagnetic waves, numerical techniques, antennas, remote sensing, and computer applications for electromagnetic education. He has published 58 technical journal articles and 12 book chapters on applied electromagnetics, antenna design, and microwave subjects, and presented over 193 papers at professional conferences. Dr. Elsherbeni is a Senior Member of the Institute of Electrical and Electronics Engineers (IEEE). He is the Editor-in-Chief for the Applied Computational Electromagnetic Society (ACES) Journal and the Electronic Publishing Managing Editor of ACES. His honorary memberships include the Electromagnetics Academy and the Scientific Sigma Xi Society. 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. He was the Chair of the Educational Activity Committee for the IEEE Region 3 Section from 2000 to 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 design, and data acquisition using network analyzers. Dr. Smith has published widely in these areas, and has over 200 total publications including journal papers, technical reports, book chapters, and paper presentations. He has advised or co-advised 46 MS thesis and PhD dissertations, and has received six awards for outstanding teaching and scholarship at the University of Mississippi. He is a Life Senior Member of the IEEE, and 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. Charles E. Smith was born in Clayton, Alabama, on June 8, He received the BEE, MS, and PhD degrees from Auburn University, Auburn, Alabama, 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 late 1968, he accepted the position of Assistant Professor of Electrical Engineering with the University of Mississippi, University, MS, and he advanced to the rank of Associate Professor in He was appointed Chair of the Department of Electrical Engineering in 1975, and he is currently Professor and Chair 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 Kai-Pong Lee received his BSc and MSc degrees from Queen s University, Canada, in 1961 and 1963, respectively, and his PhD degree from Come11 University in 1966, all in Electrical Engineering. He held research appointments at the University of California, San Diego ( ), the National Center for Atmospheric Research ( ), National Oceanic and Atmospheric Administration ( ), UCLA (summer 1975), and NASA (summers 1986, 1987). He was AssistantiAssociate Professor at the Catholic University of America, Washington, DC ( ), LectureriSenior LectureriReader at the Chinese University of Hong Kong ( ), and Professor at the University of Akron, Ohio ( ). He was the founding head of the Department of Electronic Engineering at the City University of Hong Kong ( ). He served as Professor and Chair of the Department of Electrical Engineering at the University of Toledo from 1988 to 1995, and Chair and Lapierre Professor of the Department of Electrical Engineering at the University of Missouri-Columbia from January, 1996, to December, He joined the University of Mississippi as Dean of Engineering in January, 2001, Professor Lee worked on plasma waves and instabilities from , and on antennas since His publications include a textbook (Principles of Antenna Theory, Wiley, 1984), an edited book (Advances in Microstrip and Printed Antennas, Wiley-Interscience, 1997), several invited book chapters on microstrip antennas, 149 journal articles, and 121 conference papers. / E Antenna s and Propagation Magazine, Vol. 44, No. 5, October