Modeling and Simulation of Carbon Nanotubes based Patch Antenna for WLAN Applications

Transcription

1 Technology Volume 1, Issue 2, October-December, 2013, pp , IASTER Online: , Print: Modeling and Simulation of Carbon Nanotubes based Patch Antenna for WLAN Applications 1 Rajendra R. Patil, 2 Vani R.M, 1 P.V. Hunagund 1 Department of Applied Electronics, Gulbarga University, Gulbarga 2 University Science Instrumentation Center, Gulbarga University, Gulbarga ABSTRACT This paper presents modeling and simulation of microstrip patch antenna using carbon nanotube (CNT) for wireless local area networks (WLAN) applications in Industrial, Scientific and Medical band (ISM). Here we model CNT material instead of copper metal as radiating element of the patch antenna. In this work, simulations were carried out using IE3D software for conductivity and resistivity values of CNT patch for the proposed antenna, as electric properties of the radiating patch influence the antenna characteristics. Antenna parameters like bandwidth, return loss, and radiation efficiency are studied. Simulation results validate the good performance of the proposed CNT patch antenna along with copper metal based patch antenna. Keywords: Carbon Nanotube, Proximity Coupled Patch Antenna, WLAN. I. INTRODUCTION Micro strip patch antennas (MPA) have gained a lot of importance in wireless communication systems for being low profile, light weight, low cost and compact that can be readily integrated into printed circuit technology. In spite of advantages, these antennas have some disadvantages like narrow impedance bandwidth (BW), low efficiency and low power handling capacity [1]. Narrow bandwidth is a serious limitation of the antenna. Different shapes of conducting patches (copper) like square, rectangular, dipole, circular, elliptical and triangle etc are being used in micro strip antenna. Radiating patch conductivity is one of the material characteristics that determine antenna performance and limits the applications of antenna. Inaccurate fabrication procedure, corrosion and oxidation of conducting patch can limit the performance and application of antenna. Recently researchers have shown use of various composite materials such as conducting polymer, silver nano particle ink, metal-organic conductive ink etc as radiating patch instead of pure metals [2-4]. Recently conductive carbon nano tubes (CNT) are used in radiating element that led to the development of low cost and light weight patch antennas. One of experimental investigation of use of carbon nano tube arrays on the metal surface led to enhancement of electro-magnetic radiation of the patch antenna [5]. However one of the biggest challenges in working with nano material like CNTs is the ability to make reliable electrical contact with other conductive parts of patch antenna such as feed line, matching transformer, and stub etc. This electrical unreliable contact makes it difficult to determine the RF properties of the patch antenna. Recently Fabio Urbani et al have successfully demonstrated contactless electro-magnetic coupling between radiating patch (nanomaterial) and antenna feeding mechanism (bulk copper strip line) that eliminates physical reliable electrical contact between feed line and patch known as aperture coupled micro strip patch antenna (ACMPA) [6]. 87

2 Here we present a design of other most popular antenna feeding arrangement known as proximity coupled micro strip patch antenna (PCMPA) that uses CNTs as a radiating patch. Here also there is no physical reliable electrical contact exists between feed line and radiating patch of the antenna. Hence this type of antenna provides radiation from CNT patch through indirect feed without having physical contact between feed and patch. The coupling between radiating patch and feed line will be through electro-magnetic field. Compared to other types of antennas like micro strip line feed, coaxial feed, and aperture coupled feed, PCMPA antenna has the largest bandwidth as high as 13% [7]. CNTs have been of great interest in nano electronics and nano antenna applications, since its discovery by S. Lijima of Japan in 1991, due to their favorable mechanical, thermal, electrical and electronic properties. CNTs exhibit electrical conductivity as high as copper (Cu) and can rise as high as 10 6 to 10 9 for pure metallic CNT because of structural quantization [8]. The electrical conductivity of CNTs depends upon type of CNTs (SWCNT-single wall CNT or MWCNT-multiwall CNT), properties and loading, and the characteristic of the network throughout matrix. II. ANTENNA DESIGN In microstrip patch antennas, circular patch also termed as circular disk, is the most preferred configuration after rectangular patches. The main advantage of a circular MPA configuration compared to its rectangular geometry is that circular patch occupies less physical area. Thus in applications such as arrays, circular geometries are preferred. The geometry of the proximity coupled antenna employing circular disk is illustrated in Fig 1. The circular patch is fed by proximity coupled microstrip line embedded between two dielectric substrates [9]. Patch radius, feed line length, and placing one end of feed line exactly at the centre of and below the radiating patch controls the resonant frequency. However fabrication of PCMPA is somewhat more difficult. The antenna was designed to operate at a resonant frequency of 5.8 GHz and input impedance of 50 Ω. Table 1 shows design specification for the proposed PCMPA and Table 2 shows design parameters for both copper as well as CNT radiating patch. (a) (c) Figure 1. (a) PCMPA Geometry, Top substrate, and (c) Bottom substrate Table 1. Design Specifications Table 2. Design Data for Copper & CNT Patch Parameter Value Parameter Value Resonant Frequency f r (GHz) 5.8 Copper Patch Conductivity (S/m) Substrate1 height h 1 (mm) 1.6 Copper Patch Thickness (micron) 17 Substrate2 height h 2 (mm) 1.6 CNT ballistic conductivity (S/m) Permittivity ε r of substrates 4.4 CNT Patch Thickness (micron) 17 Permeability µ r of substrates 1 Permittivity ε r of Cu and CNT 1 FR4 material loss tanδ m Permeability µ r of Cu and CNT 1 88

3 The circular patch antenna is designed using cavity model and the radius r of the disk is given by [9]: c ( f rc) 110 = (1) 2πr ε where c= cm/s is the speed of light in vacuum, r is the radius of the circular patch, and ε r is the relative dielectric constant of one side of FR4 substrate. Radius of patch antenna calculated form equation (1) is bigger than actual radius of about mm. Mentor Graphics IE3D version simulator is used to get best design parameter for circular patch [10]. IE3D is a full-wave, method-of-moments (MoM) based EM tool for the design of general 3D and planar structures like micro strip patch antenna and 2D inductors. It solves Maxwell's equations in integral form and its solutions include the wave effects, discontinuity effects, coupling effects, and radiation effects. From simulation copper patch radius is around 6.2 mm and feed line dimensions width and Length is 3 mm and 15 mm with respect to 50Ω characteristic impedance. III. SIMULATION OF CIRCULAR PCMPA ANTENNA r (a) Figure 2. Simulated Proximity coupled MPA. (a) Top view, and side view The simulated model of PCMPA is illustrated in Figure 2. Simulation is carried out for modeled copper patch and CNT patch antennas as per data given in Table 2. For CNT patch conductivity is varied from 10 8 to 10 9 S/m. Due to complexity in structure it is assumed that CNT particles are uniformly distributed in patch region and smooth surface is formed. The modeled Cu and CNT patch antennas are simulated for the frequency sweep from 4 GHz to 7 GHz. CNT patch types are from composite layer to pure metallic one. Here composite refers to CNT particles added with some polymer materials. IV. RESULTS The comparison of return loss and bandwidth between Cu and CNT patch antennas are listed in Table 3. Return loss versus frequency and radiation pattern characteristics are illustrated through figures 3-4. The antenna resonant frequency, bandwidth, and return loss for Cu and CNT antenna were obtained from the return loss versus frequency graph. Also, the 2D pattern, gain(g), directivity(d), and radiation efficiency ( η) for Cu and CNT antenna were obtained from simulations radiation pattern. From the Table 3 we can conclude that with carbon nano tube as radiating patch, antenna meets the desired specification defined for conventional patch antenna. However CNT based patch antenna is having some advantages over conventional patch antenna like no metallic loss, corrosion less, reduced skin effect, lower density, and high thermal conductivity. 89

4 Table 3. Simulation Result Radiating Patch Type Conductivity (S/m) f r (GHz) RL (-db) BW (MHz) G D η Cu CNT (a) Figure 3. Cu patch antenna (a) Return loss vs. frequency 2D Radiation Pattern Figure4. CNT patch antenna (a) Return loss vs. frequency 2D Radiation Pattern V. CONCLUSION In this paper we have designed modeled and simulated CNT based proximity coupled micro strip patch antenna for WLAN applications. The CNT patch antenna performance is compared to conventional copper patch antenna and a good agreement has been achieved through simulation. The gain, directivity, far field radiation and efficiency of CNT patch antenna found not to be significantly different when compared with conventional copper patch antenna. CNT based patch antennas are useful for some applications where light weight and robust systems are crucial. It can be concluded that carbon nano tune is the promising candidate as conducting patch material for micro strip antennas. 90

5 VI. ACKNOWLEDGEMENTS The authors acknowledge their thanks to UGC, New Delhi for sanctioning the Mentor Graphic s IE3D simulation software under major research project, which is most useful and reliable for designing of micro strip antennas. Author R.R.P would like to convey sincere thanks to President, Principal and Dean of Appa Institute of Engineering & Technology, Gulbarga for constant support and encouragement for carrying research work. REFERENCES [1] John D Kraus, Ronald J Marhefka, Ahmad S Khan, Antennas and Wave Propagation ( 4e, Tata McGraw Hill, 2011) [2] H. Rmili, J. L. Miane, H. Zangar, and T. Olinga, Design of microstrip-fed proximity-coupled conducting polymer patch Antenna, Microwave and Optical Technology Letters, 2006, [3] L. Yang, A. Rida, R. Vyas, and M. M. Tentzeris, RFID tag and RF structures on a paper substrate using inkjet-printing technology, IEEE Transactions on Microwave Theory and Techniques, vol. 55, no. 12, 2007, [4] Prabir K. Patra, Paul D. Calvert, Steven B. Warner, Textile Based Carbon Nanostructured Flexible Antenna, NTC Project No: M06-MD01 (2006). [5] Qi Zhu, Weifeng Liu, Hualiang Zhang, and Hao Xin, Experimental study of microwave radiation of carbon nanotube arrays, Applied Physics Letter Letters, Vol. 95, Issue. 8, 2009, [6] F. Urbani, D.W. Stollberg, and A. Verma, Experimental Characterization of Nanofilm Microstrip Antennas, IEEE Transactions on Nanotechnology, vol. 11, Issue 2, 2012, pp [7] D. M. Pozar, A Reciprocity Method of Analysis for Printed Slot and Slot-Coupled Microstrip Antenna, IEEE Transl. Antennas Propag, vol. 34, No. 12, pp , [8] Prabhakar R. Bandaru, Electrical properties and applications of carbon nanotube structures, Journal of Nanoscience and Nanotechnology, Vol. 7, 2007, [9] Balanis, C. A, Antenna Theory Analysis and Design, John Wiley & Sons, Wiley India (P) Ltd, [10] Mentor Graphics IE3D Software version 14.65,