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Dual band Minkowski fractal slot antenna for WLAN applications
Venkateshwar reddy V N.V.S.N Sarma Research scholar, Department of Professor, Department of Electronics and Communication Engineering Electronics and Communication Engineering National Institute Of Technology, Warangal National Institute Of Technology, Warangal Warangal, India Warangal, India [email protected] [email protected]
Abstract— A novel circularly polarized fractal paper design of dual CP antenna for WLAN 2.4 slot microstrip antenna is presented. GHz and 5.8 GHz applications by employing Perturbation to the structure for circular Minkowski fractal slot antenna is attempted. polarization is introduced by replacing the sides of the square patch with asymmetrical II. ANTENNA GEOMETRY fractal curves. A rotated fractal slot by 450 is embedded in the middle of the patch for dual Fractal geometries are generated from an band CP radiation. The simulated 10-dB original square patch by the application of a return loss bandwidths are 10%, 5.2% at 2.4 generator method iteratively. A Minkowski curve GHz and 5.8 GHz respectively. The proposed is generated as indicated in Fig. 1.The straight line antenna covers the WLAN bands at 2.4 GHz is divided into three equal sections. The central and 5.8 GHz. The gain of the antenna over the section is replaced with some indentation depth both operating bandwidths is more than 4-dBi. (D). This process is repeated to get higher iteration order fractal curves. The proposed fractal Index Terms — Circular polarization; antenna can be obtained by replacing the sides of Asymmetry; WLAN bands; gain. the square patch with Minkowski fractal curves. A fractal slot which is a scaled version of the I. original Minkowski patch rotated by 450 is INTRODUCTION embedded in the middle of the main patch to generate dual CP radiation. The proposed antenna Microstrip antennas are used in a wide range of is printed on RT duroid substrate with thickness applications because of their low profile, low 3.2mm, relative permittivity 2.33, loss tangent volume and low cost advantages. In space 0.019 and fed at probe feed point (F). The applications the signal changes its polarization suggested fractal slot antenna is depicted in Fig. 2. arbitrarily when travelling through ionosphere. To avoid loss of the signal due to this, special Iteration 0 antennas are preferred to radiate the signal in circular polarization (CP). Most of the single band circularly polarized Iteration1 Indentation depth (D) antennas are designed by introducing asymmetry in the structure using slits along corners [1]-[3] and unbalanced slots on the patch [4]-[6]. Dual band circularly polarized antennas are: stacked Fig. 1. The generation of Minkowski fractal curve. patch [7], multiple U slots [8] on the patch etc. that are reported earlier. However, designing dual band antennas using fractal slot concept has not Dx been adequately reported in open literature. In this to end length (L1) of the patch is 36 mm. The proposed antenna without fractal slot generates single CP band at 2.4 GHz.
TABLE I SUMMARIZED DIMENSIONS OF THE PROPOSED ANTENNA Parameter Dimensions Parameter Value (mm)
L1 36 Dx 0.22
L2 0.35*L1 Dy 0.11 =12.6
W2 0.15*L1 = 5.4 F (7,7) Patch To generate dual band CP operation an
asymmetrical fractal slot introduced in the middle of the main patch. The generated second CP band Substrate is mainly because of the embedded slot. The simulations are carried out using commercial IE3D and HFSS electromagnetic simulators and are depicted in Fig. 3. The first CP band at 2.4 GHz is mainly because of the strong current
distribution along the fractal curves of the main patch and for second band it is along the fractal Probe feed curves of the slot as shown in Fig. 4. The
Fig. 2. The proposed fractal slot antenna. simulated axial ratio plot is shown in Fig. 5. The gain vs frequency plot is pictured in Fig. 6. It is III. RESULTS AND DISCUSSIONS observed that proposed antenna provides more To excite two orthogonal modes of equal than 4-dBi gain at both the CP bands. Dimensions amplitude and 900 phase-shift for CP, the opposite of the antenna are given in Table 1. sides of the square patch are replaced with asymmetrical Minkowski fractal curves. The end
Fig. 3. The simulated return loss characteristics of the proposed fractal antenna using HFSS and IE3D.
Fig. 5 The axial ratio plot.
IV. CONCLUSIONS
A novel fractal slot antenna is proposed for WLAN applications. Without using stacked patch technique two bands are generated by the suggested asymmetrical fractal structure. For the simulation of the designed structure IE3D and HFSS electromagnetic simulators are employed. The nominated antenna generates good circular polarization at both the bands with 3-dB axial ratio bandwidths of 1.6% and 3% respectively at 2.4 GHz and 5.8 GHz. The simulation results show that the presented antenna designed over a single layer substrate is very useful for WLAN. (a) (b)
Fig. 4 The simulated current distribution on the patch: (a) 2.4 GHz, and (b) REFERENCES 5.8 GHz.
Fig. 6 The Gain vs Frequency plot.
There is a deviation in the IE3D and HFSS simulated return loss curves. However, IE3D assumes default infinite substrate and ground plane, where as in HFSS substrate and ground plane are finitely defined. So, HFSS results are considered for bandwidth calculations. The simulated 10-dB return loss and 3-dB axial ratio bandwidths of the first band at 2.4 GHz are 10% and 1.6%, for second band at 5.8 GHz they are 5.2% and 3% respectively. The simulated radiation pattern of the proposed antenna at 2.4 GHz is depicted in Fig. 7.
Fig. 7. Radiation pattern at 2.4 GHz. circular slots,” IEEE Trans. Antenna Propag.,vol. 56, no. 3, pp. 882- 886, 2008. [6] Nasimuddin, Xianming Qing, and Zhi Ning Chen, “Asymmetric- [1] P.C Sharma and K C Gupta, “Analysis and optimized design of single Circular Shaped Slotted Microstrip Antennas for Circular Polarization Feed Circularly Polarized Microstrip Antennas,” IEEE Tran. Antenna and RFID Applications,” IEEE Trans. Antenna Propag., vol. 58, no. Propag., Vol. 31, No. 3, pp. 949-955, 1983. 12, pp. 3821-3828, 2010. [2] Chen Wen-Shyang, Kin-Lu Chum-Kum and Wong, “Novel Compact [7] S. Du, Q. X. Chu, and W.Lio, “Dula-Band Circulalry Polarized Circularly Polarized Square Microstrip Antenna,” IEEE Trans. Stacked Square Microstrip Antenna With Small Frequency Ratio,” Antenna Propag., vol. 44, no. 10, pp. 1399-1402, 1996. Journal of Electromagnetic waves and applications, vol. 24, pp. 1599- [3] Nasimuddin, Xianming Qing, and Zhi Ning Chen, “Compact 1608, 2010. Asymmetric-Slit Microstrip Antennas for Circular Polarization,” [8] Payam Nayeri, K. F. Lee, Atef. Z.Elsherbeni, and Fan Yang, “Dual- IEEE Trans. Antenna Propag., vol. 59, no. 1, pp. 285-288, 2011. Band Circularly Polarized Antennas Using Stacked Patches With [4] Kin-Fai Tong and Ting-Pong Wong, “Circularly Polarized U-Slot Asymmetric U-Slots,” IEEE Trans. Antenna Propag., vol. 10, pp. Antenna,” IEEE Trans. Antenna Propag., vol. 55, no. 8, pp. 2382- 492-495, 2011. 2385, 2007. [5] Tzong-Chee Yo, Chien-Ming Lee, Chen-Ming Hsu and Ching-Hsing Luo, “Compact Circularly Polarized Rectenna With Unbalanced