Abstract—A new CPW fed

International Journal of Information and Electronics Engineering, Vol. 2, No. 2, March 2012 A CPW Fed E-Shaped Reconfigurable Antenna with Frequency Diversity Ch. Sulakshana and L. Anjaneyulu Abstract—A new CPW fed E-shaped reconfigurable Antenna with frequency diversity is designed and analyzed in this paper. The basic antenna consists of CPW fed E-shaped Patch antenna which operates at 5.8GHz which falls in IEEE 802.11 WLAN/RFID applications. The reconfigurability in frequency is obtained by connecting the switches in basic antenna by use of PIN diodes. By controlling the switches the antenna can be operated at three different frequencies namely 8.5GHz, 6.18GHz and 8.76GHz. The return loss of -28dB, -28.2dB,-33.07dB and -38.17dB are observed at 5.8GHz, 8.5GHz, 6.18GHz and 8.76GHz respectively. Two dimensional radiation patterns with elevation angles, gain, and efficiency of about 70% are also obtained. The compact aperture area of the antenna is 35mm X 30mm. The thickness of the substrate is 1.5mm. The proposed antenna is described and simulated results are illustrated. The results of antenna are simulated by using Zeeland’s MOM based IE3D tool. Index Terms—CPW feed, frequency diversity, patch antenna, reconfigurable antenna. I. INTRODUCTION With the enormous development of wireless communication technologies, the use of multiband antennas is increasing to meet different applications in wireless communication like Wi-Fi, Bluetooth, WiMAX, WLAN, and PCS. Hence the topic of reconfigurable antennas is gaining great attention. These antennae are researched extensively and achieved improvements to some extent through the projects like RECAP (Reconfigurable Aperture Program) conducted by DARPA [1]. Intelligent or Smart antennas are suitable for 3G and 4G technologies. The property of these antennas is to respond automatically by changing the radiation pattern, operating frequency to meet large number of wireless services that operate over wide frequency bands. Practically it is not possible to provide one antenna for each of these services. These antennas are replaced by single reconfigurable antenna which satisfies all the services by reconfiguring the operating frequency [2]. It is desirable to combine multiple antenna functions into a single antenna system to reduce antenna dimensions, cost and performance [3]. Due to the additional degree of freedom provided by the reconfigurable antennas, there is increased system performance [4]. The diversity features of reconfigurable antennas are operating resonant frequency, polarization, radiation pattern [5]-[9]. Recently, due to its many attractive features such as wide bandwidth, low cross polarization, radiation loss, less dispersion, uniplanar nature, no soldering point, and easy integration with active devices or monolithic microwave integrated circuits (MMICs), the coplanar waveguide (CPW)-fed antenna has been used as an alternative to conventional antennae for different wireless communication systems [10]. In this paper, a brief description of frequency reconfigurable antenna which includes antenna design and geometrical layout is presented in section II and finally the simulation results of return loss, radiation pattern, antenna gain and efficiency are given in section III. Simulations are carried out using Zeeland’s ‘Method of Moments’ based commercial IE3D (Integral Equation 3-Dimensional simulator). IE3D simulator is preferred than other RF CAD tools because of its high efficiency, high accuracy and low cost with windows based graphic interface that allows interactive construction of 3D and multilayer metallic structures as a set of polygons. II. STRUCTURE AND DESIGN OF PROPOSED RECONFIGURABLE ANTENNA The geometrical configuration of the proposed CPW fed E-shaped Reconfigurable Antenna is shown in Fig.1. The designed antenna is etched on a single layer of low cost FR4 dielectric substrate which is 35 X 30 mm2 in dimension. The antenna is symmetrical with respect to the longitudinal direction; whose main structure is an E-shaped Patch and a strip with Co-planar waveguide (CPW) feed line. The geometrical parameters are adjusted carefully and finally the antenna dimensions are obtained to be W1 = 30mm, W2 = 5mm, W3 = 6mm, W4 = 8mm, W5 = 2mm, W6 = 2mm, W7 = 1mm, L1 = 15.3mm, L2 = 3.6mm, L3 = 12mm, L4 = 2mm, d=1.5mm, εr = 4.3. The gap spacing between ground plane and CPW feed line is g=0.4mm. The substrate thickness t=1.5mm. The two switches are introduced in the structure namely S1 and S2. The switches S1 and S2 connect two rectangular patch lines that are present in the E shape as shown in Fig.1. In order to obtain frequency diversity, the two switches are made ON and OFF in four different modes which is given in Table I. The ON and OFF conditions of switches are realized by forward and reverse biasing of PIN diodes. Ideally, when a forward bias is applied to make the switch ON, the switch would have low impedance characteristic, acts as short and the current can flow through the diode. On the other hand, when a reverse bias is applied to make the switch OFF, the Manuscript received January 5, 2012; revised February 29, 2012. Ch. Sulakshana is with Jawaharlal Nehru Technological University Hyderabad, India (e-mail: sulakshana312ster@gmail.com). L. Anjaneyulu is with the Department of Electronics and communications engineering at National Institute of Technology, Warangal, India 174 International Journal of Information and Electronics Engineering, Vol. 2, No. 2, March 2012 switch exhibits high impedance characteristic and acts as open circuit which implies that there is no connection. antenna at 8.5GHz. Fig. 4(b) depicts the simulated gain (dBi) of the antenna versus frequency (GHz) and radiating efficiency versus the frequency. It is observed that gain of 4.7dBi and antenna efficiency of about 99.88% is obtained. TABLE I: FOUR MODES OF SWITCHES Case 1 2 3 4 Switch S1 OFF OFF ON ON Switch S2 OFF ON OFF ON C. Case 3 The S-parameters curve, radiation pattern, antenna gain and efficiency of antenna when S1 is ON and S2 in OFF condition are shown in Fig 5(a)-7(a). Fig.5 (a) depicts the return loss (dB) versus frequency (GHz). It is observed from the figure that the return loss of -33.07dB at 6.18GHz with -10dB band width of 600MHz is obtained. This antenna is suitable for C-band application. Fig.6(a) depicts the measured radiation pattern which gives Eφ polarization pattern in the elevation cuts (y–z plane and x–z plane) for the antenna at 6.18GHz. Fig.7 (a) depicts the simulated gain (dBi) of the antenna versus frequency (GHz) and radiating efficiency versus the frequency. It is observed that gain of 2.91dBi and antenna efficiency of about 70% is obtained. D. Case 4 The S-parameters curve, radiation pattern, antenna gain and efficiency of antenna when both the switches S1 and S2 are ON are shown in Fig 5(b)-7(b). Fig.5(b) depicts the return loss (dB) versus frequency (GHz). It is observed from the figure that the return loss of -38.17dB at 8.755GHz with -10dB band width of about 1.09GHz is obtained. Fig.6(b) depicts the measured radiation pattern which gives Eφ polarization pattern in the elevation cuts (y–z plane and x–z plane) for the antenna at 8.755GHz. Fig.7(b) depicts the simulated gain (dBi) of the antenna versus frequency (GHz) and radiating efficiency versus the frequency. It is observed that gain of 5.15dBi and antenna efficiency of about 99.96% is obtained. Fig. 1. Geometry of the proposed reconfigurable antenna. III. INFERENCES FROM SIMULATED RESULTS AND DISCUSSIONS To investigate the performance of the proposed antenna configurations in terms of achieving the required results, a commercially available Moment Method based CAD toolIE3D, was used for required numerical analysis and obtaining the proper geometrical parameters in Fig.1. E. Effect of Change in Switch Position The effect of change in switch position is evaluated. By keeping both switches in ON condition, the switch S1 position is moved from 0.5mm distance which is indicated by ‘d’ in Fig.1 to 4.0mm and simulated. The corresponding return loss curves are observed and plotted. The change in resonant frequency and return loss for different switch positions are tabulated in Table II and the graph showing comparative curves for the same is shown in Fig.8. After few repeated simulations using IE3D simulator, it is observed that by increasing distance (d) to 1.5mm the return loss increases to -38dB and it is also observed that there is no change in resonant frequency which is 8.55GHz, and also efficiency in case 4 is increased from 75% to 99%. Hence, d=1.5mm is taken as an optimum value in the geometry. A. Case 1 The S-parameters curve, radiation pattern, antenna gain and efficiency of antenna when both the switches S1 and S2 are in OFF condition are shown in Fig 2(a) – 4(a). Fig.2 (a) depicts the return loss (dB) versus frequency (GHz). It is observed from figure that a return loss of -28dB at 5.8GHz with -10dB band width of 897MHz is obtained. This antenna is suitable for RFID/IEEE 802.11a WLAN (5.725GHZ-5.875GHz) Applications. Fig.3 (a) depicts the measured radiation pattern which gives Eφ polarization pattern in the elevation cuts (y–z plane and x–z plane) for the antenna at 5.8GHz. Fig.4(a) depicts the simulated gain (dBi) of the antenna versus frequency (GHz) and radiating efficiency versus the frequency. It is observed that gain of 2.8dBi is obtained and antenna efficiency of about 70% is obtained. B. Case 2 The S-parameters curve, radiation pattern, antenna gain and efficiency of antenna when switch is S1 OFF and S2 is in ON condition are shown in Fig 2(b) – 4(b). Fig. 2(b) depicts the return loss (dB) versus frequency (GHz). It is observed from the figure that the return loss of -28.2dB at 8.5GHz with -10dB band width of 1390MHz is obtained. Fig. 3(b) depicts the measured radiation pattern which gives Eφ polarization pattern in the elevation cuts (y–z plane and x–z plane) for the Fig. 2. Simulated return loss of the antenna (a) when both switches are OFF. 175 International Journal of Information and Electronics Engineering, Vol. 2, No. 2, March 2012 Fig. 3. Simulated radiation pattern of the antenna (a) At 5.8GHz. (b) At 8.5GHz. (b) when S1 is OFF and S2 is ON. Fig. 4. Gain and efficiency of the antenna (a) when both switches are OFF. (b) When both the switches are ON Fig. 5.Simulated return loss of the antenna (a) when S1 is ON and S2 is off. Fig. 6. Simulated radiation pattern of the antenna (a) At 6.18GHz. (b) when S1 is OFF and S2 is ON. 176 International Journal of Information and Electronics Engineering, Vol. 2, No. 2, March 2012 (b) when both the switches are ON Fig. 7. Gain and efficiency of the antenna (a) when S1 is ON and S2 is OFF. TABLE II: EFFECT OF CHANGE IN SWITCH S1 POSITION ON RESONANT FREQUENCY AND RETURN LOSS Distance (d in mm) 0.5 1.0 1.5 2.0 2.5 Resonant frequency (fr in GHz) 8.55 8.55 8.55 8.55 9.28 Return loss (S11 in dB) -30.0 -32.9 -38.3 -28.9 -23.9 Finally the results of the proposed reconfigurable antenna are concluded in Table III. Fig. 8. A comparative graph showing return loss curves for different positions of switch S1 when both the switches are turned ON. TABLE III: RESULTS Antenna Parameters Return loss (dB) Operating Frequency (GHz) Bandwidth (MHz) Antenna Gain (dBi) Antenna Efficiency (%) Case1 Case 2 Case 3 Case 4 -28 -28.2 -33.07 -38.2 5.8 8.5 6.18 8.76 897 1390 600 1090 2.8 4.7 2.91 5.15 70 99.88 70 99.96 IV. CONCLUSION In this paper, a novel reconfigurable CPW fed E- shaped Patch antenna is presented. This antenna is compact in comparison to existing antennas. It operates at the frequency bands 5.8GHz, 8.5GHz, 6.18GHz and 8.76GHz among which 5.8GHz is found applicable for RFID/IEEE 802.11 WLAN application. This antenna is meeting desired antenna gain and efficiency at different operating frequency bands. REFERENCES [1] VSWR 1.09 1.08 1.05 1.03 Application RFID/WLAN - C-Band - [2] [3] [4] [5] [6] [7] [8] (b) At 8.5GHz. [9] 177 J. Zhang, A. Wang, P. Wang, “A Survey on Reconfigurable Antennas,” in Proc. International conference on Microwave and Millimeter wave Technology, 2008, Vol.3, pp.1156-1159, April 2008. R.-Y. Chou, C.-Y. Wu and S.-H. Yeh, “Switchable Printed Monopole Antenna with frequency Diversity for WiFi/2.6GHz WiMAX/3.5GHz Applications,” in Proc. TENCON 2007 - 2007 IEEE Region 10 Conference, pp.1-3, Oct. Y. Yashchyshyn, “Reconfigurable Antennas by RF Switches Technology,” in Proc. MEMSTECH’2009, Polyana-Svalyava (Zakarpattya), UKRAINE, pp. 22-24, April 2009. T. L. Roach, G. H. Huff, and J. T. Bernhard, “On the applications for a Radiation Reconfigurable Antenna,” in Proc. Adaptive Hardware and Systems, AHS, Second NASA/ESA Conference, pp. 7-13, Aug 2007. E. Nishiyama, M. Aikawa, and S. Sasaki, “Polarisation switchable slot-ring array antenna,” IEEE Microwaves, Antennas & Propagation, Vol.2 No.3,pp. 236-241, 2008. G. Ruvio, M. J. Ammann, and Zhi Ning Chen, “Wideband Reconfigurable Rolled Planar Monopole Antenna,” IEEE Transactions On Antennas And Propagation, vol. 55, no. 6, pp.1716-1767, June 2007. D. Peroulis, K. Sarabandi, and P. B. K. Katehi, “Design of reconfigurable slot antennas,” IEEE Transactions on Antennas and Propagation, Vol. 53, pp. 645-654, 2005. S.-H. Hsu, K. Chang, “A Novel Reconfigurable Microstrip Antenna with Switchable Circular Polarization,” IEEE Antennas and Wireless Propagation Letters, vol. 6, pp. 160-162, 2007. S. V. Shynu, G. Augustin, C. K. Anandan, P. Mohanan, and K. Vasudevan, “Triple Slot Arm Loaded Reconfigurable Dual frequency International Journal of Information and Electronics Engineering, Vol. 2, No. 2, March 2012 Microstrip Antenna using Varactors,” in Proc. Antennas and Propagation Society Int. Symposium IEEE[C], Vol.2B, pp. 609-612, July 2005 [10] R. N. Simons, Coplanar Waveguide circuits, Components and systems, John Wiley & sons, Inc., 2001, ch.1. Ch. Sulakshana was born in Hyderabad, India in 1985. She received B.Tech degree (2007) in Electronics and Communication Engineering from G.Narayanamma Inst. of Technology and Science affiliated to Jawaharlal Nehru Technological University Hyderabad, India. She received M.Tech degree (2010) in Communication Systems from in National Institute of Technology Tiruchirappalli, India and currently pursuing PhD degree from National Institute of Technology Warangal, India. Her field of study is Reconfigurable Antennas and other areas of interest are Microwave Engineering and Antenna wave propagation. She has publications in 2 International Journals, 8 International conferences and one National Conference. 178 L. Anjaneyulu was born in 1967 in India. He obtained his B.Tech (ECE) in 1989 from Nagarjuna University, India, M.Tech from R.E.C (N.I.T), Warangal, India in 1991 and Ph.D in 2010 from N.I.T, Warangal, India. His areas of interest include Computer Networks, Electromagnetic Field Theory, Microwave & Radar Engineering, and Neural Networks & Fuzzy Logic Systems. He worked as Project Officer at Institute of Armament Technology, Pune, India for 5 years from 1991 and involved in the design of Surface borne and Air-borne Radar systems for clutter measurement application. Later, he worked as Staff Scientist at Helios Systems, Madras, India for 2 years and engaged in the development of Radio Wave propagation assessment software modules for ship-borne radars. He has been with the department of Electronics and communications engineering at National Institute of Technology, Warangal, India since 1997. Dr. Anjaneyulu has completed few defence R&D Projects and has 22 papers to his credit in National and International Conferences and journals. He is a reviewer for Defence Science Journal, New Delhi. He has conducted several short term training programmes as a coordinator in the areas of Computer Networks, Microwave and Radar Engineering, Electromagnetic Fields. He is a Life member of ISTE and a member of IEEE.