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  Integrated Dual-Purpose Narrow/Ultra-Wide Band Antenna for Cognitive Radio Applications Yingsong Li, Wenxing Li College of Information and Communications Engineering, Harbin Engineering University, Harbin, Heilongjiang, 150001, CHINA; Raj Mittra Department of Electrical Engineering, The Pennsylvania State University, University Park, PA 16802, USA   Abstract   —An integrated narrow/ultra-wideband antenna composite is proposed for use in cognitive radio applications. The proposed antenna consists of two slot antennas with individual feeds sharing the same substrate. The ultra-wideband (UWB) antenna covers the entire UWB band from 3.1GHz to 10.6GHz and is used for channel sensing. The integrated narrow band antenna operates at 8.2GHz to 9.4GHz communicate with other wireless devices. The two ports have a good isolation, which is better than -10dB. The design is suitable for cognitive radio applications where the UWB antenna is required for spectrum sensing, and where the narrowband antenna is used for reconfigurable operation, which can be tuned over a wide bandwidth by changing its dimensions of the isosceles triangular radiation patch. I.   I  NTRODUCTION  With the increase of wireless communications, there has  been an increase in the demands for smart and agile radio frequency devices that not only sense the signals but also respond to the RF changes in various communication environments [1]. Many different applications require frequency agility with software control ability, such as in a cognitive radio environment where the antenna systems need to fulfill the requirements for reconfigurable multi-service and multiband components. For these reasons, several reconfigurable have been designed for cognitive radio applications [2-5]. An effective method for ding this is to use  physical alteration of the antenna parts via a rotational motion to achieve the reconfigurable characteristic [1]. However, the structure of such a proposed antenna is complex, and the center frequency is difficult to control. An alternative method is to combine the wideband antenna and narrowband antenna together and to connect to the narrow and wideband antennas via a shorting pin [3]. However, the resulting antenna is difficult to control when utilizing taper-fed signal line. In addition, although the proposed antennas have been realized for cognitive applications [4-5] by using switches, the diodes in these switches leak electromagnetic waves and deteriorate the radiation patterns. To overcome the shortcomings of the previous proposed antennas, an integrated antenna comprising of two wide slot configurations are proposed in this paper, with space wide slots incorporated in the same substrate. The sensing antenna is designed by using cantor set fractal structure design, while the reconfigurable communication antenna is a triangular monopole. II.   G EOMETRY OF THE ANTENNA Fig.1 illustrates the geometry of the integrated narrow/ultra-wideband antenna. The proposed integrated narrow/ultra-wideband antenna is printed on a substrate with a relative permittivity of 2.65, a loss tangent of 0.002 and a thickness of h=1.6mm. The size of the antenna is 27×21mm 2  (L×W). The proposed antenna consists of a wide slot structure of rectangular shape; a polygonal slot structure; a cantor set fractal radiation patch; a stepped impedance stub radiation  patch that uses an isosceles triangular patch with a base-side of 3mm; two ports fed by using a 50 Ω  coplanar waveguide (CPW) -fed structures. The 50 Ω  CPW-fed structure consists of the CPW transmission signal strip line with a signal strip widths W3= W4=3.6mm and a gap between the CPW ground plane and the transmission signal strip with widths S1= S2=0.2mm. Fig.1 Geometry of the proposed antenna 978-1-4673-0462-7/12/$31.00 ©2012 IEEE  Ⅲ .  RESULTS AND DISCUSSIONS  To evaluate the performance of proposed antenna, the antenna was investigated by using the Ansoft High Frequency Structure Simulator (HFSS). The optimized dimensions are as follows: L=27mm,W=21mm,L1=11.2mm,W1=18mm,L2=2.5 mm,W2=8mm,L3=1.5mm,L4=3.5mm,L5=1mm,H=1.2mm,g=0.8mm,L6=2mm,L7=3mm,x=8.4mm,y=12mm.The simulated results are presented in Fig.2, which shows that the proposed narrow band antenna covers the frequency range of 8.2GHz to 9.4GHz with a return loss better than -10dB, while the cantor set fractal UWB antenna has an impedance bandwidth of 7.8GHz. The UWB antenna covers a wide frequency band, ranging from 2.74GHz to 10.7GHz, making it suitable for channel sensing in cognitive radio. An antenna suitable for channel sensing and reconfigurable communication should  possess an omnidirectional radiation pattern to verify whether Fig.2 Simulated return loss and coupling (a) (b) (c) (d) Fig.3 Radiation patterns of the proposed antenna the present design has this characteristic. Its radiation patterns have been investigated by using HFSS. To obtain the radiation  pattern of the sensing antenna, port-1 of the reconfigurable antenna is matched with a 50 Ω  load impedance, whereas to obtain the radiation patterns of reconfigurable communication antenna, port-2 of the sensing antenna is matched with a 50 Ω  load impedance. The simulated radiation patterns are shown in Figs.3 (a)-(c) of the sensing antenna for frequencies of 3.5GHz, 7.5GHz and 9GHz. The sensing antenna can prove a nearly omni-directional characteristic in the H-plane and a monopole-type radiation patterns in the E-plane. Fig.3 (d) presents the radiation pattern of the reconfigurable communication antenna at a frequency of 8.8GHz. It can be seen from Fig.3 (d) that the antenna also has a nearly omni-directional characteristic in the H-plane and a monopole-type radiation pattern in the E-plane. The proposed narrow/ultra-wideband antenna is incorporated into the same substrate, which reduces the space requirements and places the two antennas required for cognitive radio communication in the same plane. Ⅳ .  CONCLUSION  In this paper, a novel antenna design for cognitive radio communication has been proposed. The proposed antenna consists of two CPW-fed wide slot antennas. The ultra-wideband antenna is suitable for channel sensing and the narrow antenna is a stepped-impedance stub structure using triangular radiation patch. The narrow band antenna can reconfigure the frequency which satisfies reconfigurable communication for other wireless devices. The two wide-slot antennas are integrated on the same substrate. The proposed two-port antenna has a mutual coupling level less than -10dB in the entire operation band. The antenna is a suitable candidate for future cognitive radio communication. Experimental results for the proposed antenna will be included in the presentation and the design of a circuit that controls the reconfigurable communication antenna will also be discussed future. R  EFERENCES   [1]   Y. Tawk and C. G. Christodoulou, “A new reconfigurable antenna design for cognitive radio”, IEEE Antennas and Wireless Propagation Letters, vol.8, 2009,pp.1378-1381. [2]   F. Ghanem, P. S. Hall and J. R. Kelly, “Two port frequency reconfigurable antenna for cognitive radios”, Electronics Letters, vol.45, 2009,pp.534-536. [3]   E. Ebrahimi, J. R. Kelly and P. S. Hall, “A reconfigurable narrowband antenna integrated with wideband monopole for cognitive radio applications”, IEEE Antennas and Propagation Society International Symposium( APSURSI), 2009. [4]   J. W. Baik, S. Pyo, T.H. Lee, and Y.S. Kim, “Switchable printed Yagi-Uda antenna with pattern reconfiguration”, ETRI Journal, vol.31, 2009,pp.318-320. [5]   G. P. Jin, D.L. Zhang and R.L. Li, “Optically controlled reconfigurable antenna for cognitive radios applications”, Electronics Letters, vol.47, 2011,pp.948-950.
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