A MICROSTRIP ANTENNA FOR WIRELESS APPLICATION

Transcription

1 A MICROSTRIP ANTENNA FOR WIRELESS APPLICATION Harsh A. Patel 1, J. B. Jadhav 2 Assistant Professor, E & C Department, RCPIT, Shirpur, Maharashtra, India 1 Assistant Professor, E & C Department, RCPIT, Shirpur, Maharashtra, India 2 Abstract: A microstrip fed dual-band coplanar antenna for wireless local area network is prepared. The antenna is made up of a rectangular center strip and two lateral strips printed on a dielectric substrate and excited using a 50Ω microstrip transmission line. The antenna generates two separate resonant modes to cover 2.4/5.2/5.8 GHz WLAN bands. The experimental data show that the antenna can provide two impedance bandwidths of 330 MHz centered at 2.4 GHz, and 1.23 GHz centered at 5.4 GHz. Keywords: Microstrip slot antenna, Dual-band antenna, wireless local area networks (WLANs). INTRODUCTION In modern wireless communication systems, multiband antenna has been playing a very important role for wireless service requirements. Wireless local area network (WLAN) has been widely applied in mobile devices such as handheld computers and intelligent phones. This technique has been widely recognized as a viable, cost-effective, and high-speed data connectivity solution, enabling user mobility. In practice, IEEE WLAN standards consist of 2.4-GHz ( GHz), 5.2- GHz ( GHz), and 5.8-GHz ( With the rapid development of the modern wireless communication system, antenna design has turned to focus on wide multiband and small simple structures that can be easy to fabricate. To adapt to the complicated and diverse WLAN environments, several promising dual- and multiband antenna designs have already been proposed in [1] [12]. In [3], a crooked U-slot and a radial stub make the antenna achieve dual-band operations. It has a simple structure to be fabricated easily, but only dual bands can be supplied the same as the antennas in [1] and [2]. In [4] [6], though the proposed monopole antennas have good characteristics for both WLAN and WiMAX applications, they are complicated in structures and large in size. Besides slot and monopole antennas, there are many other general implementations for multiband applications, such as patch antennas [7] [9], dipole antennas [10], [11] and antennas using composite metamaterial resonators [12], etc. Compared to regular antennas, the slot antenna fed by microstrip line has better characteristics, including wider bandwidth, less conductor loss, and better isolation between the radiating element and feeding network [13]. In this communication, a compact differential dual-frequency antenna is presented. The radiating element with half-guided wavelength is arranged on two stacked layers and connected through via All rights reserved by ISSN :

2 holes. Moreover, a reflecting 75 GHz) frequency bands. Patches is introduced and connected with the ground plane through two via holes that a new resonant frequency closing to f 1 is excited. The antenna can operate at 2.4 GHz and 5.2 GHz and 5,8 GHz bands, with good simulated results. In addition, good radiation performances have been achieved at both bands. 1. ANTENNA DESIGN Fig. 1. Coplanar wave guide with finite lateral strips and the feed point when printed on a substrate of thickness h and relative permittivity ε r. (a) Top view. (b) Cross-section view. The simulation has been done using method of moment based Zeland IE3D electromagnetic solver to bring out the resonant conditions of the structure. For study an open circuited section of finite coplanar waveguide as shown in Fig. 1 with characteristic impedance 50Ω.in this case, center strip width W 1 =3 mm, lateral strip width W 2 =15 mm, g=0.3 mm, length l=15 mm, on FR4 substrate with ε r =4.7, thickness mm is selected and its frequency versus return loss characteristics over a wide frequency range (1 10 GHz) is observed. The process has been repeated for different W 1 values, at different feed locations along the width of center strip. The characteristics of the structure when the feed point is at center (p 1 ) and when the feed point is shifted to the corner (p 2 ), as shown in Fig. 1, have been illustrated in Table I. When feed point is at the center, the structure behaves as an open circuited coplanar wave guide transmission line. Table 1. IE3D simulation for coplanar wave guide W 1 Feed point at center (P 1 ) Feed point at corner (P 2 ) (mm) F 0 (GHz) Return loss (-db) F 0 (GHz) Return loss (-db) 3 No Resonance No Resonance No Resonance No Resonance No Resonance All rights reserved by ISSN :

3 Fig. 2. Simulated current distribution of (a) conventional coplanar wave guide and (b) coplanar waveguide with feed point at the corner. W 1 = 3 mm, W 2 = 15 mm, l = 15 mm, g =0.3, ε r = 4:7, and thickness h = 1:6 mm. The microstrip transmission line is the best suited feed for this antenna configuration due to its bottom ground layer, which is required to excite the second resonant mode of the antenna. Fig. 3. Geometry of the proposed dual-band microstrip line fed compact coplanar antenna printed on a dielectric substrate. (a) Cross sectional view.(b) Top view. The following design procedure can be used to design this antenna with good radiation characteristics. The design procedure is as follows. 1. Select any substrate with relative dielectric constant ε r and thickness h, and calculate the width W 3 of the microstrip transmission line for 50Ω characteristic impedance. 2. Calculate width of the center strip W 1 using the following: (1) Where c is the velocity of light. All rights reserved by ISSN :

4 Since the field components are not confined to the substrate alone the effective dielectric constant has to be used in calculations instead of relative permittivity of the substrate 3. The length of the three rectangular strips is then calculated As 4. Width of the lateral conductor s w2 is calculated using the following: 5. Gap separating center strip from the lateral strips is then calculated (5) The coefficients 0.15 and in (3) and (5), respectively, were obtained after exhaustive experimental and simulation studies. These values were arrived at from curve fitting technique. 6. The ground plane dimensions are calculated using the following: (2) (3) (4) (6) The coefficients 0.12 and 0.98 were derived empirically after studying the effect of ground plane on the two resonant frequencies. 7. The two extreme corners of the lateral conductors are connected to ground plane of the microstrip line using vias or conducting pins. (7) Fig. 4 (a). Simulated return loss for the compact microstrip fed dual band coplanar antenna for 2.4/5.2/5.8 GHz WLAN application. All rights reserved by ISSN :

5 Fig. 4 (b). Simulated return loss for the compact microstrip antenna for 2.4/5.2/5.8 GHz WLAN application in IE3D. Fig. 4 (C). Smith chart of compact microstrip antenna for 2.4/5.2/5.8 GHz WLAN application in IE3D. EXPERIMENT AND RESULTS The dimensions of the antenna to operate in 2.4/5.2/5.8 GHz WLAN bands, calculated using the for FR4 substrate with ε r =4.7, loss tangent 0.02 and thickness h=1.6 mm are w1=12.5 mm, w2=5 mm, l=9 mm, g=0.8 mm, ground plane dimensions L=10 mm and W=50 mm. The lower band covers 2.4 GHz WLAN, and the upper band covers 5.2/5.8 GHz WLAN bands. The antenna is Simulated. Fig. 4 shows the simulated results of the antenna. WLAN band. The simulated bandwidth for the upper band is 1.23 GHz ( MHz,) about 22% centered at 5.26 GHz) and covers the two WLAN bands ( MHz) easily. The large impedance bandwidth in the two bands is due to the increased surface area of the strips. Effects of All rights reserved by ISSN :

6 various dimensions such as l, w 1 and w 2 of the antenna on FR4 substrate are studied to confirm the two modes of the antenna. Fig.4(d) Gain of compact microstripantenna for 2.4/2.8/5.8GHZ for WLAN application. The radiation patterns and gains are also measured, and the gains are measured at the broadside direction by the substitution method. Fig. 4(d) shows gains antenna. It can be seen that good radiations in E- and H-planes are obtained. This is because the proposed antennas have a ground plane of 50 mm 20 mm. Fig. 4(d) shows the measured gains in two bands. We are trying to improve results of simulation for this antenna. We will get it soon. CONCLUSION In this communication, a compact differential dual-frequency antenna is simulated. The radiating element with a half guided wavelength is distributed on two layers and connected through via holes, thus the size of the antenna can be reduced effectively. In order to improve the bandwidth at f 1 the ground plane is introduced, and connected with the ground plane through via holes. Experimental results show that the antenna can operate at 2.4 and 5.2 GHz bands, respectively. At f 2 the antenna with the reflecting board has a wider impedance bandwidth of 3.7%, better than that of 2.0% of the antenna without the reflecting board. Also, good radiation performances have been achieved at both bands. The proposed antenna is of low cost and compact size thus it is suitable for wireless communication applications. A compact coplanar antenna for covering the band of frequency 2.4, 5.2 and 5.8 GHz WLAN has been simulated. The antenna use two resonant modes exited on coplanar wave guide structure obtain suitably selecting feed point on wide signal strip. The generalized design procedure for antenna for any two band of operation has been simulated. The compact o antenna with the excellent radiation characteristics will be our goal to achived. REFERNCE [01] R. K. Raj, M. Joshep, C. K. Aanandan, K. Vasudevan, P. Mohanan, A new compact microstrip-fed dual-band coplanar antenna for WLAN application IEEE Trans. Antennas Propag., vol. 54, no. 12, pp , Dec [02] H.-D. Chen, J.-S. Chen, and Y.-T. Cheng, Modified inverted-l monopole antenna for 2.4/5 GHz dual- band operations, IEE Electron. Lett., vol. 39, no. 22, Oct All rights reserved by ISSN :

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