Prosiding Seminar Kebangsaan Aplikasi Sains dan Matematik 2013 (SKASM2013) Batu Pahat, Johor, 29 30 Oktober 2013 DESIGN A DOUBLE PATCH ANTENNA WITH COPLANAR WAVEGUIDE FOR WIRELESS APPLICATION Afiza Nur Jaafar 1, Mohd Tarmizi Ali 2, Zairi Ismael Rizman 3, Rosmawati Shafie 4, Suziyani Rohafauzi 5, Nur Hafizah Rabi ah Husin 6 1 Faculty of Electrical Engineering afiza4980@tganu.uitm.edu.my 2 Faculty of Electrical Engineering Universiti Teknologi MARA (UiTM) Malaysia 40450 Shah Alam, Selangor mizi732002@salam.uitm.edu.my 3 Faculty of Electrical Engineering zairi576@tganu.uitm.edu.my 4 Faculty of Electrical Engineering rosma5455@tganu.uitm.edu.my 5 Faculty of Electrical Engineering suziy4867@tganu.uitm.edu.my 6 Academy of Language Studies nurha5690@tganu.uitm.edu.my In this paper, the design of double patch antenna with coplanar waveguide (CPW) is demonstrated. The proposed structure consists of rectangular patches which are printed on the both sides of Flame Retardant 4 (FR-4) substrate. The antenna is designed to operate at 5.1-5.8 GHz frequency which can be applied in wireless application. For the research, a Computer Simulation Technology (CST) Microwave Studio software is selected as a tool to design the antenna structure and to perform the simulation as well. From the simulated return loss, gain and radiation patterns of the antenna, it was demonstrated that the structure is able to apply for wireless application due to its resonant frequency at 5.4 GHz. The performance of the designed antenna was analyzed such as bandwidth, gain, return loss, VSWR, and radiation pattern. Keywords: FR-4 substrate; wireless application; double patch antenna; coplanar waveguide; 5.1-5.8 GHz. 91
Pure Mathematics 1. INTRODUCTION Microstrip antennas have been introduced over 30 years, and it started to be popular in 1970s. This type of antenna technology is expanding and most of the limitations have been improved recently (Garg, 2001; Matin & Sayeed, 2010). The popularity is also due to its characteristic such as low profile, simple to fabricate using modern printed circuit technology, and easy to analyze or fabricate (Balanis, 2012). However, the major disadvantage of the microstrip antenna is by its narrow bandwidth (Chen, 2004). Several techniques were introduced to improve the impedance bandwidth such as employed a wide band impedance matching, stacked patches and used a thicker substrate. However, by employing the wide band impedance matching, it creates a potential to offer an unwanted radiation at higher frequency in the presence of wide lines used for matching over a wide band. While by increasing the height of dielectric, the axial ratio of the patch may increase following the excitation of higher order modes (Telikepalli, 1995). Another method to improve the bandwidth is by using a coplanar waveguide (CPW) feeding method. It has a simple configuration, repeatability and low cost (Shanmuganantham, Balamanikandan & Raghavan, 2008). CPW consists of a center strip with two ground planes located parallel to and in the plane of the strip. Even though the CPW will result the antenna to produce slightly higher losses and poor power handling capability, but it able to produce broadband output signal (Varshney, Gupta, Kumar & Suraj, 2011). Besides it offers wider bandwidth, it also has better impedance matching and easy to integrate with active device or monolithic microwave integrated circuits. The antenna which can produce a wide bandwidth signal in 5.1-5.8 GHz frequency range is suitable for ultra-wideband wireless transmission such as for IEEE 802.11a Wireless Local Area Network (WLAN) application which also can be used in commercial wireless application (Shanmuganantham, Balamanikandan & Raghavan, 2008; Varshney, Gupta, Kumar & Suraj, 2011). 2. METHODOLOGY The procedures of designing and analyzing the double patches antenna with CPW feed are explained. By identifying the antenna operating frequency, the width (W) and length (L) of patch antenna can be determined by using the following equation (Balanis, 2012; Matin & Sayeed, 2010): W c f r 2 r 2 1 (1) 92
Prosiding Seminar Kebangsaan Aplikasi Sains dan Matematik 2013 (SKASM2013) Batu Pahat, Johor, 29 30 Oktober 2013 L 2 f r c r (2) The patches dimension are calculated at the resonant frequency, f r = 5.4 GHz, velocity of light, c = 3x10 8 ms -1, and the dielectric constant, ε r = 4.7. Certain parameters of antenna need to be optimized in order to obtain a desired result. The step is repeated until the results show the antenna is operated efficiently as per determined. Then the process is continued with a fabrication process. CPW structure is incorporated in the proposed design to enhance the usable bandwidth. In (3) shows the thickness of the patch (t) and the rule to determine the gap size (g), between ground and the feeder line, which is related to the CPW dimension. t 0. 1g (3) 3. ANTENNA DESIGN Generally the process to design the proposed antenna is started by identifiying the antenna operating frequency. This is due to the resonance frequency will give the significant effect to the size and antenna geometry. By using the chosen frequency, the width and length of antenna can be calculated according to (1), (2) and (3). After that, the patch antenna is designed by using CST software. In this software, double rectangular patches are designed, followed with the CPW structure on the top layer of antenna. Next is the simulation process to check whether the antenna performances are met the requirement or not. If the performances are not satisfied, the parameters of antenna need to be optimized until the simulation output produces the desired result. Figure 1 shows the geometry design of double patch antenna with integration of CPW structure. (a) Top view 93
Pure Mathematics (b) Side view Fig. 1. Geometry design of double patch antenna with CPW. The geometry design of the microstrip double patch antenna with CPW is illustrated in Figure 1 (a) and 1 (b). The dimension is measured in millimeter (mm). The structure composes of an antenna element on the FR-4 substrate. Originally, each patch with a dimension of 12.7 mm x 16.3 mm and thickness of 0.035mm is printed on the both sides of FR-4 substrate. The substrate has a dimension of 32.5 mm x 55 mm, a dielectric constant, ε r = 4.7 and thickness, h = 1.6 mm. FR-4 is selected due to its wide availability and low cost (Chen, Huang & Lin, 2008). The size of the substrate is optimized from 32.5 mm x 55 mm to 88 mm x 64 mm in order to achieve a higher gain value. The CPW feeding technique is chosen to obtain a broader bandwidth range. Besides that, the technique which etches the slot and the feed line on the same side of the substrate eliminates the alignment problem needed in other wideband feeding techniques such as aperture coupled and proximity feed (Varshney, Gupta, Kumar & Suraj, 2011). 4. RESULTS AND DISCUSSION Front side of the substrate is printed with a single rectangular patch and CPW component while the back side is printed with another element of rectangular patch. The patch at the back side is to promote a higher gain value of the antenna while the CPW is to increase the usable bandwidth. From the simulation, gain obtained is 8.2 db. Fig. 2. S-parameter (S 11 ) from simulation. 94
Prosiding Seminar Kebangsaan Aplikasi Sains dan Matematik 2013 (SKASM2013) Batu Pahat, Johor, 29 30 Oktober 2013 Figure 2 indicates the simulation result for the input return loss. The bandwidth is determined by referring to the value of return loss which is below than -10 db. From the simulation result, the bandwidth is measured from 4.9-5.8 GHz. The S 11 for the simulated signal is -33.5 db at the frequency of 5.41 GHz. From the figure, the percentage of bandwidth is calculated to 16.88 %. Fig. 3. Simulation value of VSWR. Figure 3 shows the value of voltage standing wave ratio (VSWR) during simulation process. VSWR indicates how much power is reflected back or transferred into a cable (Chen, 2004). Hence, a perfect matched antenna would have a VSWR of 1:1 (Stutzman & Thiel, 2012). Simulation result shows the VSWR is 1.036 at 5.4 GHz frequency. The result has fulfilled the standard design requirement as the ratio of VSWR is < 2. Fig. 4. 3D Radiation pattern from double patch antenna with CPW for 5.1-5.8 GHz. 95
Pure Mathematics Fig. 5. 2D Radiation pattern from double patch antenna with CPW for 5.1-5.8 GHz. Figure 4 and 5 represent the radiation pattern which radiated by the proposed antenna in 3D and 2D view respectively. Radiation pattern is a graphical representation of the radiation properties of an antenna 1 (Stutzman & Thiel, 2012). The simulation is demonstated from 5.1-5.8 GHz with center frequency of 5.4 GHz. From the result obtained, the proposed antenna produces 92.5 degree angular width at 3 db. The result obviously shows that the double patch antenna with CPW is able to produce high gain value besides has a wide bandwidth. 5. CONCLUSION In the paper, a microstrip double patch antenna with CPW has been designed, simulated, optimized and analyzed by using CST software. The antenna s performance was analyzed for bandwidth, gain, VSWR and radiation pattern. The broad bandwidth has been achieved by using the proposed antenna which incorporated with CPW technique. The proposed antenna operates in the range of frequency from 4.9 GHz to 5.8 GHz for VSWR less than 2. The results also indicate that the double patch antenna with CPW is able to make the gain to increase up to 8.2 db. From the simulation, the percentage of bandwidth is 16.88 %. Therefore, it can be concluded that the double patch antenna with CPW is capable to enhance the usable bandwidth with greater gain value. Hence, the proposed structure would be greatly suitable to overcome the lower gain and narrow bandwidth in microstrip patch antenna. Acknowledgments The author would like to thank to Associate Professor Dr. Tarmizi Ali as a supervisor and members of Microwave Technology Centre (MTC), Universiti Teknologi Mara (UiTM) for their help in this research. 96
References Prosiding Seminar Kebangsaan Aplikasi Sains dan Matematik 2013 (SKASM2013) Batu Pahat, Johor, 29 30 Oktober 2013 Balanis, C. A. (2012). Antenna Theory: Analysis and Design, New Zealand: John Wiley & Sons. Chen, J.-S.; Huang, C.-H. & Lin, S.-Y. (2008). Design of a 5.2/5.8 GHz High Gain Antenna Array. IEEE Antennas and Propagation Society International Symposium, 1-4. Chen, W. K. (2004). The Electrical Engineering Handbook, London: Elsevier Academic Press. Garg, R. (2001). Microstrip Antenna Design Handbook, United State: Artech House. Matin, M. A. & Sayeed, A. I. (2010). A Design Rule for Inset-Fed Rectangular Microstrip Patch Antenna. WSEAS Transactions on Communications, 9(1): 63-72. Shanmuganantham, T.; Balamanikandan, K. & Raghavan, S. (2008). CPW-Fed Slot Antenna for Wideband Applications. International Journal of Antennas and Propagation, 2008, 4 pages. Stutzman, W. L. & Thiel, G. A. (2012). Antenna Theory and Design, John Wiley & Sons. Telikepalli, R. (1995). Design of a Wide Band Microstrip Patch for Use in a Phased Array Antenna for Mobile Satellite Communications. IEEE Canadian Conference on Electrical and Computer Engineering, 2: 1173-1175. Varshney, L.; Gupta, V. R.; Kumar, H. & Suraj, P. (2011). CPW-Fed Broadband Microstrip Patch Antenna. International Journal of Advanced Engineering & Application. 97
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