DESIGN OF A RECTANGULAR SHAPE OMEGA SLOTTED MICROSTRIP PATCH ANTENNA FOR WLAN/WIMAXWIRELESS APPLICATIONS

Rev. Roum. Sci. Techn. Électrotechn. et Énerg. Vol. 61, 1, pp. 63 67, Bucarest, 2016 DESIGN OF A RECTANGULAR SHAPE OMEGA SLOTTED MICROSTRIP PATCH ANTENNA FOR WLAN/WIMAXWIRELESS APPLICATIONS MD REZWANUL AHSAN 1, MOHAMMAD TARIQUL ISLAM 1, MOHAMMAD HABIB ULLAH 2 Key words: Patch antenna, Microstrip feed, Wireless local area network/ worldwide interoperability for microwave access (WLAN/WiMAX), Inverse omega. In this article, an optimized rectangular shaped patch antenna loaded with inverse omega shape and horizontal slots, and feed by microstrip line is designed for WLAN/WiMAX applications. The expected resonant frequency mode and desired bandwidth are obtained through numerous simulation processes and utilizing the built-in optimizing tool in high frequency structural simulator (HFSS). The optimized design of the antenna gives impedance bandwidths (reflection coefficient S11<-10 db) of 440 MHz (2.32 to 2.76 GHz), 570 MHz (327 to 3.84 GHz) and 1190 MHz (4.9 to 6.09 GHz) with the main resonant frequency at 2.54, 3.63 and 5.24 GHz respectively. The proposed antenna also attained appreciable gain characteristics and almost symmetrical/stable radiation patterns which can cover 2.4/5.2/5.8 GHz WLAN bands and 3.5/5.5 GHz WiMAX bands. 1. INTRODUCTION The recent boom in technological development of wireless communications systems has demanded the utilization of low cost antenna with compact size and multiband functionalities. Microstrip antennas are widely popular for their compact size, easy manufacturing processes and ability to integrate with the existing wireless components [1]. The wireless local area network (WLAN) and worldwide interoperability for microwave access (WiMAX) are commonly applied to portable wireless devices like smartphones, tablets and laptops, thus necessitated to the accumulation of more than one frequency band in a single antenna module. The IEEE standard for WLAN communications are: 2.4 GHz (2.4 2.484 GHz), 5.2 GHz (5.15 5.35 GHz) and 5.8 GHz (5.725 5.825 GHz) bands. The WiMAX frequency bands are: 2.5 GHz (2.5 2.69 GHz), 3.5GHz (3.4 3.69 GHz) and 5.5 GHz (5.25 5.850 GHz) [2]. Various techniques are employed to achieve dual-band functionality, like slot loading [3], fractal shape [4], stub loading [5], adding parasitics [6], multilayer patch [7], electromagnetic bandgap structure [8], meandered strips [9] and so forth. For covering the WLAN and WiMAX bands simultaneously, several researchers have proposed antennas with different geometrical structures and sizes. The planar antennas such as a double C-shape strip antenna [10], rectangular and trapezoidal slotted antenna [11], circular patch with defected ground [12], S-shaped strip with notched rectangular radiating patch [13] have offered for WLAN/WiMAX frequency band operations. Although, the mentioned multiband antennas have some advantages, but still there are some performance criteria need to be improved. Moreover, the reported antennas may have a complex geometrical structure or larger in size or resonant frequency are not sufficiently tuned or have narrow bandwidth. This article presents the design and performance analysis of compact microstrip antenna with inverse-omega shape slot for WLAN/WiMAX applications. The simple design of the antenna has a symmetrical structure along y-axis and fed by 50 ohm microstrip line through coaxial cable. The effects of different slots in producing the frequency bands are numerically analyzed and the key parameters are regulated according to obtain the best performance out of the antenna. The result analysis shows that the proposed antenna is able to operate in dual frequency bands that cover 2.4/5.2/5.8 GHz WLAN bands and 3.5/5.5 GHz WiMAX bands. Fig. 1 Detail geometrical configuration of the proposed antenna: a) top view; b) bottom view. 2. ANTENNA CONFIGURATION The geometrical structure of the dual-band antenna is illustrated in Fig. 1. The antenna is designed on 1.905 mm thick Rogers duroid 6010LM microwave laminate substrate of relative permittivity 10.2, loss tangent 0.0023 and overall dimension 40 mm 35 mm. The antenna is fed by coaxial cable which is connected to the radiating patch 1 University Kebangsaan Malaysia, Dept. of Electrical, Electronic and Systems Engineering, 43600 Bangi, Selangor, Malaysia, E-mail: rezwanul.ahsan@yahoo.com. 2 University of Malaya (UM), Faculty of Engineering, Dept. of Electrical Engineering, 50603 Kuala Lumpur, Malaysia

64 Md Rezwanul Ahsan, Mohammad Tariqul Islam, Mohammad Habib Ullah 2 through 2 mm wide 5 mm long microstrip line having 50 ohm characteristic impedance. The antenna has got defected ground plane structure by employing U-shape slot on it to improve the performance of the patch antenna [14]. The commercially available and reliable electromagnetic simulation software Ansys high frequency structural simulator (HFSS) is used throughout the numerical analysis and design [15]. The details of the parametric dimensions for the proposed dual-band antenna are optimized and presented in Table 1. The final optimized design of the antenna has been evolved from the rectangular shape through numerous simulations. It is already revealed to the researchers that the antenna performance depends on the dimension of the radiating patch and can be determined by following the mathematical equations [16]. The length of the antenna has a dominant effect on bandwidth and resonance frequency. Table 1 Optimized parameters of the proposed antenna Fig. 2 Performance of different antenna structure and achieving proposed antenna. Parameter Value (mm) Parameter Value (mm) W 40 L 40 W1 14.7 L1 6 W2 14.7 L2 27.4 W3 4 L3 5 W4 19 Ls 5 Wc 18 Lc 1.5 Wd 4 Lt 1.5 Ws 2 Lg 28 Wg 32 Gt 2 Ro 12 Ri 10.5 The effect of introducing different slots on the radiating patch is plotted in Fig. 2. Here the figure shows different antenna structure and their performance in terms of reflection coefficient (Scattering parameter or S-parameter, S11) vs frequency. The design process starts with the creation of Ant-1 through horizontal slot loading at the center of the rectangular shape patch. The figure illustrates the generation of first and third resonant mode at around 2.4 and 4.94 GHz respectively. Employing the half part of the inverse-omega shape as shown in Ant-2 improves the resonance mode and assists to achieve 2 nd resonance frequency near 3.5 GHz. With the insertion of inverseomega shape slot and central slot (Ant-3), the variation of current paths become large and bandwidth becomes narrower with improved reflection coefficient. By cutting slots on the ground plane creates (Proposed antenna) unbalanced currents which allows two different resonant frequencies to merge into one and thus extends the bandwidth and overall antenna performance [17]. The inclusion of different slots and their effect are also analyzed separately through detailed parametric study. During the parametric analysis, when one parameter is set for analysis the other parameters remain as it is. Figure 3a shows the simulated reflection coefficient (S11) when the thickness of the central slot is varied. It is found that, L c = 1.5 mm gives the best performance in terms of wide bandwidth and lowest reflection coefficient. In a similar manner, the radius of the inverse-omega shape (R i ) is adjusted from 9.0 mm to 11.0 mm which gives varying thickness of the slot. It is found that R i = 10.5 mm has achieved acceptable bandwidth and reflection coefficient which is shown in Fig. 3b. Fig. 3 Effect of varying (a) thickness of central slot (Lc) on the reflection coefficient (S11) and (b) radius (Ri) on the reflection coefficient (S11). 3. RESULTS AND DISCUSSIONS Figure 4 exhibits the simulated reflection coefficient (S11) against frequency of the proposed dual band microstrip patch antenna. From the figure it can be seen that, three distinct frequency bands are obtained with impedance bandwidth for S11 < 10 db. The simulated resonant frequencies can be observed at 2.54 GHz, 3.63 GHz and 5.24 GHz which good impedance matching. The impedance bandwidth at 10 db reflection coefficient (S11) can be found ranging from 2.32 to 2.76 db, 3.27 to 3.84 db and

3 Microstrip patch antenna for wireless applications 65 4.90 to 6.09 db for lower middle, and upper band respectively. Moreover, resonant modes are merged with the principle resonance frequency to make the bandwidth wide enough: 3.39 GHz is merged with 3.63 GHz and 5.81 is merged with 5.24 GHz. more or less equal to 30 db. Additionally, the proposed dual-band antenna has achieved 3 db beamwidths for E- plane is wider than that of H-plane. This phenomenon may arise from the fact that the antenna has got symmetrical geometric structure. Fig. 4 Simulated reflection coefficient (S11) vs. frequency of the proposed dual-band antenna covering WLAN/WiMAX. The simulated surface current distribution of the antenna is presented in Fig. 5, which can help to understand the working functionality of the radiating patch. The figure here shows the distribution of current on the radiating surface of the patch for 2.54, 3.63 and 5.24 GHz and the color map. It can be seen that the radiating patch holds different current density for every frequency and intensity of current is increased with the increased operating frequency. Cutting slots on the radiating patch reasonably disturb the mean current path of any base frequency and assist to provide a change of resonance characteristics. This is due to the fact that the electric and magnetic field distribution changes because of lengthening the path for surface current around the slots. For this reason, the current mainly concentrates near the edge of the slots and additional resonant frequency generated with wider bandwidth due to the increased current path. Figure 5 clearly shows that for higher frequency the surface currents are much disturbed and increased intensity can be observed on the surrounding edge of the slots. The peak gain curve and radiation efficiency curve are shown against frequency in Fig. 6. The average gains of the proposed antenna are found 2.57 dbi, 3.38 dbi and 5.2 dbi for lower, middle and upper frequency bands respectively. Whereas the maximum radiation efficiencies are seen in the figure 74.3 % at 2.4 GHz, 80.47 % at 3.75 GHz and 86.22 % at 5.5 GHz. Fig. 7 exhibits the simulated Smith chart of the proposed microstrip antenna. It can be observed from the figure that three resonant modes of operation are marked which are fall inside the 2:1 voltage stranding wave ration (VSWR) circle and other values like impedance and VSWR are also listed in tabular form. The simulated E-plane and H-plane radiation patterns at 2.54 GHz, 3.63 GHz and 5.24 GHz are shown in Fig. 8. The figure shows that due to the symmetrical geometry of the patch, the proposed dual-band antenna has offered nearly omnidirectional and symmetrical radiation patterns except the patterns for the higher frequency band. This may be contributed due to the higher cross-polarization effect, mutual coupling miss-match and defected ground. However, for both the E- and H-plane and three operating bands, the cross polarization values are Fig. 5 Simulated surface current distribution of the proposed antenna at: a) 2.54 GHz; b) 3.63 GHz; c) 5.24 GHz. Fig. 6 Simulated gain and radiation efficiency of the proposed dual-band antenna against frequency. Fig. 7 Simulated Smith chart of the proposed dual-band antenna.

66 Md Rezwanul Ahsan, Mohammad Tariqul Islam, Mohammad Habib Ullah 4 Fig. 8 Simulated radiation pattern for the proposed dual band antenna at: a) 2.54 GHz; b) 3.63 GHz; c) 5.24 GHz. 4. CONCLUSIONS A compact rectangular shaped inverse-omega slotted dual-band antenna is proposed for WLAN/WiMAX wireless communication systems in this article. The simple geometrical structure of the proposed microstrip patch antenna occupies overall are of 40 35 mm 2. The design criteria of the antenna have been analyzed properly and the Rogers 6010LM ceramic-ptfe (Polytetrafluoroethylene) substrate is considered for the design. The ground plane of the antenna is slotted to create defected ground behavior which gives rise in bandwidth and antenna performance. The simulation result shows that the proposed antenna has achieved three distinct working bands, ranging from 2.32 GHz to 2.76 GHz, from 3.27 GHz to 3.84 GHz, and from 4.90 GHz to 6.09 GHz, which can satisfy the requirement for 2.4/ 5.2/5.8 GHz WLAN bands and 3.5/5.5 GHz WiMAX bands. The nearly omnidirectional radiation patterns and almost stable gain/radiation efficiency of the suggested dual-band antenna over the operating bands make it an appropriate candidate in WLAN/WiMAX communication systems. Received on June 15, 2015 REFERENCES 1. M. Samsuzzaman, M. T. Islam, M. J. Singh, Ceramic material based multiband patch antenna for satellite applications, Rev. Roum. Sci. Techn. Electrotechn. et Energ., 59, 1, pp. 77 85, 2014. 2. J. Pei, A.-G. Wang, S. Gao, W. Leng, Miniaturized triple-band antenna with a defected ground plane for WLAN/WiMAX applications, IEEE Antennas and Wireless Propagation Letters, 10, pp. 298 301, 2011. 3. M. R. Ahsan, M. T. Islam, M. H. Ullah, A compact multiband inverted a-shaped patch antenna for WiMAX and C-band, Microwave and Optical Technology Letters, 56, 7, pp. 1540 1543, 2014. 4. J. Malik, P. C. Kalaria, M. V. Kartikeyan, Complementary Sierpinski gasket fractal antenna for dual-band WiMAX/WLAN (3.5/5.8 GHz) applications, International Journal of Microwave and Wireless Technologies, 5, 4, pp. 499 505, 2013. 5. B. Li, Z.-H. Yan, T.-L. Zhang, C. Wang, Dual-band antenna with U- shaped open stub for WLAN/WIMAX applications, Journal of Electromagnetic Waves and Applications, 25, 17 18, pp. 2505 2512, 2011.

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