Design of Internal Dual Band Printed Monopole Antenna Based on Peano-type Fractal Geometry for WLAN USB Dongle

Transcription

1 University of Technology, Iraq From the SelectedWorks of Professor Jawad K. Ali September 12, 2011 Design of Internal Dual Band Printed Monopole Antenna Based on Peano-type Fractal Geometry for WLAN USB Dongle Ali J Salim, Department of Electrical Engineering, University of Technology, Iraq Jawad K. Ali, Department of Electrical Engineering, University of Technology, Iraq Available at:

2 1268 PIERS Proceedings, Suzhou, China, September 12 16, 2011 Design of Internal Dual Band Printed Monopole Antenna Based on Peano-type Fractal Geometry for WLAN USB Dongle Ali J. Salim and Jawad K. Ali Department of Electrical and Electronic Engineering, University of Technology, Baghdad, Iraq Abstract This paper introduces the design of a new dual-band internal printed monopole antenna structure as a candidate for WLAN (wireless local area network) USB (universal serial bus) dongle applications. The proposed antenna structure is based on the second iteration of Peano- type space-filling geometry. The antenna has been printed on a substrate with relative permittivity of 2.33 and thickness of 0.8 mm, and fed with 50 Ω microstrip line. The resulting antenna has been found to possess a compact size of 15 mm 5.6 mm, which is suitable for this application. Furthermore, the proposed antenna offers a dual resonant behavior with frequency ratio of about 2.41; resulting in bandwidths, for return loss 10 db, covering the two WLAN band standards. Modeling and performance evaluation of the proposed antenna have been carried out using the CST Microwave Studio. Simulation results of return loss, radiation patterns, and gain verify that the presented antenna represents a good solution for dual-band WLAN USB dongle applications. 1. INTRODUCTION Many USB dongle antennas for WLAN applications have been reported in the literature [1 8]. Beside the limited size constrains, these antennas must fight against other challenges such as the resulting gain, the radiation pattern, the bandwidth, and the ease of fabrication. In [1], a printed meander-line antenna has been proposed for WLAN/USB dongle; however this antenna can only operate at 2.4 GHz. Planar inverted-f antenna PIFA had been presented in [2] as a dual-band antenna for UTMS/WLAN applications. However, this antenna is considered more complex for fabrication, in spite of the compact size achieved. Another microstrip fed folded PIFA antenna has been presented in [3], but it only covers the lower WLAN band. A combined C-shaped strip and a straight strip of a compact printed monopole antenna provide two resonant paths to achieve 2.4, 5.2, and 5.8 GHz multiband operation [4]; the size of this antenna made it improper for USB dongle. A combination of meander line and Cohen-like fractal geometry has been suggested to construct a printed monopole antenna in [5]. This antenna has been found to possess suitable size and dual-band performance covering the required band for WLAN 802.1a/b/g standards; but it lacks from the relatively low gain. Another printed monopole antenna configuration for dual-wlan USB dongle has been reported in [6]. The antenna consists of two parts; a circular hook-shaped patch resonating at 2.5 GHz ISM band, and a folded monopole stub, inserted in the hook-shaped patch to produce another resonant frequency at the upper frequency band near 5.5 GHz. On the other hand, a miniaturized internal antenna design covering the 2.4 GHz WLAN and UWB (ultra wideband) system bands, for USB dongle applications, has been reported in [7]. The antenna mainly consists of a folded metal plate with two sided beveled; supported by short circuited pin connected to the ground plane, and slots in the bevel sides of the folded metal plate. A coplanar printed loop antenna fed by a coupling-feed mechanism for 2.4-GHz WLAN applications has been proposed in [8]. The antenna has noticeable compact size; making the proposed design suitable for the use within wireless devices in the lower WLAN band environment. Except for the work reported in [5], fractal geometries have not been investigated in the design of dual-band antenna for WLAN USB dongle applications. However, these geometries have been successfully used to construct antenna structures for dual-band WLAN embedded in the laptop computers [9 11]. In this paper, a printed dual-band monopole antenna is proposed for use in the USB WLAN dongle applications covering the IEEE a/b standards. This antenna is combined of a transmission line structure, based on the 2nd iteration modified Peano fractal geometry, fed with a 50 Ω microstrip line, via a printed line used for allocating the two resonating WLAN bands. 2. THE PROPOSED ANTENNA STRUCTURE The conventional Peano fractal curve has been widely used in the design of compact and multiband antennas, because of its space-filling and self-similarity properties it possesses [12 14]. Space-filling property leads to produce miniaturized antennas, while self-similarity results in antennas with

3 Progress In Electromagnetics Research Symposium Proceedings, Suzhou, China, Sept , (a) (b) (c) Figure 1: The generation process of the modified Peano pre-fractal curve up to the 2nd iteration. Figure 2: The layout of the proposed dual-band monopole antenna with respect to the coordinate system. All dimensions are in mm. multi-resonant performance. However, this fractal curve fills the space, in such a way to form a square after infinite number of iterations. Taking into consideration the size constraints imposed on the antenna for USB dongle applications; this fractal geometry does not represent a proper choice. Instead, a modified version of the conventional Peano fractal curve has been considered for this task. This Peano-type fractal geometry, as depicted in Figure 1, has been suggested to construct miniaturized microwave transmission lines, filters, capacitors, and many other passive components [15]. In this structure, the conventional Peano pre-fractal curve generator has been stretched by a factor of 0.5 in only one dimension, so the resulting fractal structure will no longer be with a square outline. Figure 1 demonstrates the generation process of the modified Peano pre-fractal curve up to the 2nd iteration. The straight line in Figure 1(a), (the initiator), has been replaced by the nine segment structure in Figure 1(b), the generator. Then, in certain iteration n, each line segment has to be replaced by the whole structure of its preceding iteration, taking into account segment scaling and orientation. Hence, the 1st iteration consists of 9 segments, and the 2nd iteration has 81 segments, and so on. If the length of the initiator line is L o, the length enclosed by any pre-fractal structure at the nth iteration n, L n is: L n = 2 n L n 1, for n 1 (1) 3. ANTENNA DESIGN Figure 2 shows the layout of the proposed dual-band monopole antenna with respect of the coordinate system. A monopole antenna, in the form of the 2nd iteration modified pre-fractal geometry, has been printed on one side of a substrate with a relative dielectric constant of 2.33 and a substrate thickness of 0.8 mm. On the reverse side of the substrate, is the ground plane of the system which has the dimensions of mm 2. The fractal part is combined with a small length of a printed transmission line, used for tuning purposes. A 50 Ω-microstrip line is used to feed the combined monopole antenna. It has been found that, the monopole antenna resonates near the standard dual WLAN bands when its length, L, of about 15 mm. In terms of the antenna parameters, the lower resonant frequency, f L is calculated

4 1270 PIERS Proceedings, Suzhou, China, September 12 16, 2011 Figure 3: The simulated return loss response of the proposed antenna together with the current distributions at the two resonating bands. (a) Figure 4: The simulated gain of the proposed antenna at: (a) the lower band, and (b) the upper band. (b) as f L = C 6L ε re (2) where C o is the speed of light in free space, ε re and is the relative effective permittivity of the substrate. 4. PERFORMANCE EVALUATION The proposed antenna has been modeled, and its performance has been calculated using the CST Microwave Studio (MWS) simulation software. The simulated return loss has been depicted in Figure 3. The simulated return loss, for S db, bandwidths range from GHz and from 5.59 to 6.1 GHz with corresponding bandwidths of about 0.74 and 0.46 GHz respectively. Figure 3 also shows the simulated current distributions at the IEEE a and IEEE b/g bands, where the current distribution implies that the realization of the two bands is attributed by the corresponding antenna parts with reddish color. The peak gain values in the two bands have been evaluated, as shown in Figure 4. In the lower frequency band, the peak gain plotted in Figure 4(a) is as large as 3.28 dbi, which is higher than

5 Progress In Electromagnetics Research Symposium Proceedings, Suzhou, China, Sept , (a) 2.4 GHz X-Y plane (b) 5.2 GHz Y-Z plane Figure 5: The simulated radiation patterns of the proposed antenna at: (a) the lower band, and (b) the upper band in the X-Y and Y -Z planes. the gain values of reported antennas [5]. The gain versus frequency, for the upper band, is plotted in Figure 4(b), where the maximum gain of copolarization is found to be of about 4.6 dbi which is also higher than that reported in [5]. Curves in Figure 5 show the simulated radiation patterns in the X-Y plane and the Y -Z plane at the two bands. Like the conventional monopole antenna, the modeled antenna has an omnidirectional radiation patterns in the Y -Z plane at the two bands, while it has the two conventional minima in the X-Y plane radiation patterns. 5. CONCLUSION In this paper, a new compact monopole dual-band antenna has been suggested to be a solution for the internal antenna for dual-band WLAN USB dongle. The proposed fractal shaped antenna has been found to offer acceptable dual-band behavior with nearly omnidirectional patterns at the two WLAN bands. In addition, the compact size of the proposed antenna makes it a good solution for the USB dongle applications. Beside the simple structure, the resulting antenna gain at the two bands is noticeably greater than what is published in the literature for other antennas of the same category. It is hopeful that this antenna finds its place for use in portable dual-band MIMO applications. REFERENCES 1. Lin, C. C., S. W. Kuo, and H. R. Chang, Internal PIFAs for UMTS/WLAN/WiMax multinetwork operations for a USB dongle, IEEE Microwave and Wireless Components Letters, Vol. 15, No. 9, , Su, W. C. and K. L. Wong, Internal PIFAs for UMTS/WLAN/WiMax multi-network operations for a USB dongle, Microwave and Optical Technology Letters, Vol. 48, No. 11, , 2006.

6 1272 PIERS Proceedings, Suzhou, China, September 12 16, Wei, J., L. Chen, X. W. Shi, and Y. W. Zhai, Design and analysis of a folded printed inverted- F antenna for bluetooth applications, 2007 International Symposium on Microwave, Antenna, Propagation and EMC Technologies for Wireless Communications, Beijing, China, Song, Y., Y. C. Jiao, H. Zhao, Z. Zhang, Z. B. Weng, and F. S. Zhang, Compact printed monopole antenna for multiband WLAN applications, Microwave and Optical Technology Letters, Vol. 50, No. 2, , Luo, Q., J. R. Pereira, and H. M. Salgado Fractal monopole antenna for WLAN USB dongle, Proceedings of 2009 Loughborough Antenna and Propagation Conference, UK, Jeong, S. J. and K. C. Hwang, Circular hook-shaped wireless USB dongle antenna with an open stub, IEICE Electronic Express Journal, Vol. 7, No. 18, , Gong, J. G., Y. C. Jiao, Q. Li, J. Wang, and G. Zhao, A miniaturized internal wideband antenna for wireless USB dongle applications, Progress In Electromagnetic Research Letters, Vol. 17, 67 74, Su, S. W., T. C. Hong, and F. S. Chang, Very compact coupled fed loop antenna for 2.4 GHz WLAN applications, Microwave and Optical Technology Letters, Vol. 52, No. 8, , Bledowski, M. and M. Kitlinski, Compact-planar monopole loop antennas for b/g WLAN systems, Microwave and Optical Technology Letters, Vol. 49, No. 9, , Guterman, J., A. A. Moreira, C. Peixeiro, and Y. Rahmat-Samii, Electromagnetic human interaction with ISM 2.4 GHz Laptop antennas, Proceedings of the 2nd European Conference on Antenna and Propagation, EuCAP 2007, Edinburgh, UK, Krzysztofik, W. J., Fractal antenna for WLAN/bluetooth multiple bands applications, Proceedings of the 3rd European Conference on Antenna and Propagation, EuCAP 2009, Berlin, Germany, Zhu, J., A. Hoorfar, and N. Engheta, Peano antennas, Digest 2003 USNC/CNC/URSI North American Radio Science Meeting, Columbus, OH, USA, McVay, J. and A. Hoorfar, Miniaturization of top-loaded monopole antennas using Peanocurves, Proceedings of IEEE Radio and Wireless Symposium, Yu, Y. and W. Wu, Miniaturized peano fractal loaded monopole antenna, Proceedings of Asia Pacific Microwave Conference, APMC 2009, Singapore, Puente, C. B., Fractal and space-filling transmission lines, resonators, filters and passive network elements, US Patent, No. 7, 538,641 B2, Apr