A simple UWB monopole antenna using half-elliptical radiator

Transcription

1 Title A simple UWB monopole antenna using half-elliptical radiator Author(s) Yang, XJ; Liu, L; Cheung, SW; Sun, YY Citation The 213 International Workshop on Antenna Technology (iwat 213), Karlsruhe, Germany, 4-6 March 213. In Conference Proceedings, 213, p Issued Date 213 URL Rights International Workshop on Antenna Technology: Small Antennas and Novel Metamaterials Proceedings. Copyright IEEE.; 213 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.; This work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4. International License.

2 213 International Workshop on Antenna Technology (iwat) A Simple UWB Monopole Antenna using Half-elliptical Radiator X. J. Yang, L. Liu, S. W. Cheung and Y. Y. Sun Department of Electrical and Electronic Engineering, The University of Hong Kong, Hong Kong, China locky937@hku.hk, swcheung@eee.hku.hk, liuli@eee.hku.hk, yysun@eee.hku.hk ABSTRACT: This paper presents the results of a simple ultrawideband (UWB) monopole antenna having an impedance bandwidth from GHz. The antenna has a half-elliptical shaped radiator with microstrip-fed and a total size of mm 3. The extremely wideband characteristic of the antenna is achieved by simply using a tapered transformer and a small square slot on the ground plane. INTRODUCTION Planar ultrawideband (UWB) monopole antennas, due to low cost, low power and low complexity, have been developed quickly for uses in wireless communications [1]. To achieve wideband operation and stable performance for planar UWB antennas, different methods have been proposed. These methods included using resonant structures [2], parasite elements [3], filters [4], slots [5], different shaped radiators [6], modifying the shape of the radiator [7], adding slots on the ground plane [8], and modifying the shapes of the ground planes [9-1]. Some researchers also combined several methods together to optimize the designs [11-13]. This paper presents a very simple design to achieve the extremely wide bandwidth for a planar monopole antenna. The antenna has a half-elliptical shaped radiator with microstrip-fed, a tapered transformer and a small square slot on the ground plane. Simulation results show that the antenna with a compact size mm 3 can achieve a bandwidth of GHz. ANTENNA DESIGN The geometry of the proposed antenna is shown in Fig. 1, which consisted of a half elliptical-shaped radiator fed by a microstrip line and a tapered impedance transformer printed on one side of the substrate and a partial-ground plane with a small square shaped slot on the other side. The antenna was designed on a Rogers substrate, RO435B, with an area of Ws Ls, having a thickness of.762 mm, a permittivity of 3.48 and a loss tangent of.4. The half elliptical-shaped radiator had a minor axis of 2 Rx in the horizontal direction and a major axis of 2 Ry in the vertical direction. The width Ws of the substrate was equal to the length of the minor axis. The width and length of the microstrip feed line were set at Wl = 1.7 mm and Ll = 5 mm, respectively, to achieve 5-Ω impedance. To achieve good matching, a tapered impedance transformer, having an upper width of Wt = 1.12 mm and a length of Lt = 3 mm, was used between the radiator and microstrip feed line. The partial-ground plane had a dimension of Ws Lg. A small square slot with size of Wslot Lslot was cut on the upper edge of the ground plane underneath the microstrip feed line to improve matching at higher frequencies and hence to widen the operating bandwidth. The antenna was optimized using computer simulation with the optimized dimensions listed in Table 1. Table 1 dimensions of antenna (mm) Ws Ls Rx Ry W1 L1 Wt Lt Lg Wslot Lslot Simulation results of parametric study showed that the parameters including the horizontal axis Rx, the vertical axis Ry, the feed gap and the upper width of the transformer Wt were the main factors for impedance matching, with Ry the main factor determining the low cutoff frequency. Computer results also have shown a full-elliptical shaped radiator could achieve the similar performance, but a half-elliptical shaped radiator having only half of the radiator area could be used to reduce the size of the antenna. The antenna in Fig. 1 was also fabricated using the optimized dimensions as shown in Fig /13/$ IEEE 145

3 (a) (b) (c) Fig. 1 Geometry of proposed antenna: (a) front view, (b) bottom view, and (c) side view. Fig. 2 Prototyped antenna RESULTS AND DISCUSSIONS The and S11 of the proposed antenna are shown in Fig. 3. It can be seen from the result that the antenna had an impedance bandwidth (S11<-1dB) of GHz. Even at the frequency of 4 GHz, the S11 did not increase sharply. In fact, it was possible to achieve an even wider bandwidth through further optimization such as adjusting the slot dimensions on the ground plane. Due to the Vector Network Analyzer used in our laboratory, we could only measure S11 up to 24 GHz. Figure 3 shows that, in the frequencies below 24 GHz, the and S11 agree quite well. The antenna was and then using the antenna measurement system Satimo Starlab. The peak gains and the efficiencies of the antenna are shown in Figs. 4 and 5, respectively. It can be seen that the gain varied from about 2.37 dbi at 3.1 GHz to about 6.25 dbi at 2.5 GHz with an average gain of 4.95 dbi across the frequency band from 3.1 to 39.9 GHz. The gain had more fluctuations which were due to the small ground plane of the antenna and also tolerance of the Starlab system. The efficiency varied from 81.% to 97.2% with an average of 89.4%. Large discrepancies were observed at low frequencies, which again was due to ground plane effects. Large discrepancies were also observed at about 15 GHz, which was due to the tolerance of the Starlab system. Figure 6 shows the and co-polarization radiation patterns of the antenna at 3.1, 16.5, 18 and 4 GHz. It can be seen that the radiation patterns in the were quite omnidirectional even up to the frequency 4 GHz. The and radiation patterns agreed well. simulation measurement -1 S11 (db) Frequency (GHz) Fig. 3 Simulated and S

4 8 6 simulation measurement 1. simulation measurement 4.8 Realized Gain (dbi) Efficiency Frequency (GHz) Fig. 4 Simulated and realized gains Frequency (GHz) Fig. 5 Simulated and efficiencies (a) (b)

5 (c) (d) Fig. 6 Radiation patterns at (a) 3.1 GHz, (b) 1 GHz, (c) 18 GHz and (d) 4 GHz CONCLUSIONS The design of a simple UWB monopole antenna with microstrip-fed having a compact size of mm 2 has been presented. Simulation results have shown that the antenna has an extremely wide bandwidth of GHz and so is well suitable for UWB applications. REFERENCE [1] Z. N. Chen, M. J. Ammann, X. Qing, X. H. Wu, T. S. P. See, and A. Cai, Planar antennas, IEEE Microwave Magazine., vol. 7, pp , 26. [2] R. A. Sadeghzadeh-Sheikhan, M. Naser-Moghadasi, E. Ebadifallah, H. Rousta, M. Katouli, and B. S. Virdee, Planar monopole antenna employing back-plane ladder-shaped resonant structure for ultra-wideband performance, IET Microwaves, Antennas & Propagation., vol. 4, no. 9, pp , September 21. [3] T. C. Martins, R. M. S. de Oliveira, and C. L. S. Sobrinho, Use of square parasite elements to increase the bandwidth of planar monopole antenna for UWB systems, 27.IMOC 27. SBMO/IEEE MTT-S International Microwave and optoelectronics conference., pp , October 27-November 27. [4] A. Barakat, and M. El-Khamy, Bandwidth extension of UWB planar antenna with band-notched characteristics, 21 IEEE Middle east conference on antennas and propagation (MECAP)., pp. 1-5, October 21. [5] H. Wang, and Y. Li, Bandwidth enhancement of a wide slot UWB antenna with a notch band characteristic, 211 IEEE 3 rd international conference on communication software and networks (ICCSN)., pp , May 211. [6] W. Naktong, and A. Ruengwaree, Increasing bandwidth of flambeau-shape monopole antenna for UWB application, th international conference on electrical engineering / electronics, computer, telecommunications and information technology (ECTI-CON)., pp , May 211. [7] R. Zaker, and A. Abdipour, A very compact ultrawideband printed omnidirectional monopole antenna, IEEE Antennas and wireless propagation letters., vol. 9, pp ,

6 [8] Y. Y. Sun, M. T. Islam, S. W. Cheung, T. I.Yuk, R. Azim, and N. Misran, Offset-fed UWB antenna with multi-slotted ground plane, 211 international workshop on antenna technology (iwat)., pp , March 211. [9] D. Chang, J. Liu, B. Zeng, and M. Liu, Impedance bandwidth enhancement for UWB slot antenna, 27. IWAT 7. International workshop on antenna technology: small and smart antennas metamaterials and applications., pp , March 27. [1] M. Leib, M. Frei, and W. Menzel, A microstrip-fed Ultra-wideband slot antenna, 29. APSURSI 9. IEEE antennas and propagation society international symposium., pp. 1-4, June 29. [11] D. Nashaat, H. A. Elsadek, E. Abdallah, H. Ellhenawy, and M. F. Iskander, Enhancement of ultra-wide bandwidth of microstrip monopole antenna by using metamaterial structures, 29. APSURSI 9. IEEE antennas and propagation society international symposium., pp. 1-4, June 29. [12] Q. Wu, R. Jin, J. Geng, and M. Ding, Printed omni-directional UWB monopole antenna with very compact size, IEEE transactions on antennas and propagation., vol. 56, no. 3, pp , March 28. [13] M. Koohestani, M. N. Moghadasi, and B. S. Virdee, Miniature microstrip-fed ultra-wideband printed monopole antenna with a partial ground plane structure, IET microwaves, antennas and propagation., vol. 5, no. 14, pp , November