Coplanar rectangular patch antenna for x band applications using inset fed technique

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  • 1. International Journal of Electronics and Communication Engineering & Technology (IJECET), INTERNATIONAL JOURNAL OF ELECTRONICS AND ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET) ISSN 0976 – 6464(Print) ISSN 0976 – 6472(Online) Special Issue (November, 2013), pp. 95-102 © IAEME: www.iaeme.com/ijecet.asp Journal Impact Factor (2013): 5.8896 (Calculated by GISI) www.jifactor.com IJECET ©IAEME Coplanar Rectangular Patch Antenna for X Band Applications Using Inset Fed Technique Arvind Singh Jadon1, Jalaj Sharma2, Ajay Prajapat3, Avanish Bhadauria4 1,3Department 2,4MEMS of Electronics & Communication,BKBIET, Pilani, India and Microsensors Group,Central Electronics Engineering Research Institute, Pilani, India 1avanish@ceeri.ernet.in ABSTRACT: This paper presents the simulation model of an inset fed Coplanar Patch Antenna for X band satellite communication. Inset feed provides an easy impedance matching and better return loss value. The simulated results show that coplanar patch antenna has high radiation efficiency and comprises of a wider bandwidth as compared to a microstrip patch antenna. A radiation efficiency of approximately 98% and an impedance bandwidth equal to 17.8% is obtained for a coplanar patch antenna. There is an increment of 10.5% in radiation efficiency of the coplanar patch antenna then microstrip patch antenna. A brief comparison between Coplanar and Microstrip Patch Antenna is also presented. All the designs presented in this paper are simulated using electromagnetic simulation software Ansoft HFSS v13. KEYWORDS: Coplanar Patch Antenna, Impedance Bandwidth, Inset Fed Technique, Microstrip Patch Antenna, Radiation Efficiency. I. INTRODUCTION From last few decades, planar antennas have been a field of interest for many researchers and scholars. With the revolution in electronic circuit miniaturization and large scale integration in the early 70’s, demand for a compact antenna with small size, which can be integrated with MMIC designs increased. Since planar antennas are substrate based antennas and their properties like ease in fabrication, and easy integration with MMIC and PCB designs, increased popularity of planar antennas and influenced large number of research in this field. Planar patch antennas have advantages like low profile, light weight and ease of fabrication. Microstrip patch antenna is the most popular of all the other type of planar antennas. It consists of a grounded substrate with a conducting patch above the substrate. But they have certain disadvantages too like low gain, narrow bandwidth and low efficiency [1]. A large number of articles and papers have been published showing different methods to increase the performance parameters of a microstrip patch antenna such as gain, bandwidth, efficiency, and polarization etc. Different type of patch shapes such as rectangular, circular, International Conference on Communication Systems (ICCS-2013) B K Birla Institute of Engineering & Technology (BKBIET), Pilani, India October 18-20, 2013 Page 95
  • 2. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME triangular, square and different polyhedron shapes have been designed and studied [2-5]. Different feed techniques and impedance matching circuits have been used so that maximum excitation power should be coupled through the feed line to the patch [6, 7]. Coplanar patch antenna is a new and better alternative of microstrip patch antennas. A coplanar patch antenna has ground and patch on the same side of the substrate with a gap width s as shown in fig.1. Since the effective dielectric constant for a coplanar antenna design is lower than microstrip antenna design, the surface wave excitation is reduced to a large extent and due to the reason coplanar antennas have high radiation efficiency and wider bandwidth. Also, coplanar patch antennas are easy to fabricate, have low radiation loss, less dispersion, uniplanar configuration and easy MEMS based reconfigurable antennas can be designed without using via holes as used in case of microstrip designs. Fig.1: Schematic Diagram of Inset Fed Coplanar Patch Antenna Impedance matching in a patch antenna is an important issue. Generally a 50Ω transmission line is considered as a feed line, because 50Ω transmission line has a very low reflection coefficient. However, impedance at the edge of the patch is generally more than 300Ω, which requires some additional impedance matching techniques. Now to couple maximum power from the feed to patch we can introduce a λ/4impedance transformer line between patch and the feed line. In case of direct feeding, the feed line is shifted on either side of the patch along the edge until an impedance of 50Ω is achieved. One more technique used to match the impedance of the patch with respect to feed line is to design an inset fed patch antenna. In general the impedance in a patch decreases from the edge to the centre of the patch, at the centre of the patch impedance is zero. Now we make a cut from the edge of the patch to that point where impedance of feed line and patch is matched and we connect feed line from that point as shown in fig.1. To our knowledge few design models of coplanar patch antenna has been reported, such as rectangular patch coplanar antennas are designed and characterized by different authors at different frequency bands [11,12], a bow tie coplanar patch antenna is also studied which gives a wider bandwidth [10]. Here in this paper we are presenting a coplanar patch antenna using inset coplanar waveguide (CPW) feed technique for X band applications. Due to its wider bandwidth and high radiation efficiency it could be applicable in many X band satellite systems. In satellite system transponder requires antenna with high radiation efficiency and wider bandwidth so as to transmit (or receive) audio, video and data signal all together. International Conference on Communication Systems (ICCS-2013) B K Birla Institute of Engineering & Technology (BKBIET), Pilani, India October 18-20, 2013 Page 96
  • 3. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME For designing the coplanar patch antenna we have used a full wave EM simulation software Ansoft HFSS v13, which works on the principle of Finite Element Method (FEM). FEM can be divided into two different methods; one uses variational analysis, and the other weighted residuals. However both the methods start with the partial differential equation form of Maxwell’s equations. The unknown field is dicretized using a finite element mesh; typically triangular elements are used for surface meshes and tetrahedrons for volumetric meshes. Both these geometries are chosen as with these geometries two dimensional and three dimensional regions respectively can be meshed [13]. II. COPLANAR PATCH ANTENNA A coplanar line is a structure in which all the conductors supporting wave propagation are located on the same plane, i.e. generally the top of a dielectric substrate. Coplanar Waveguide (CPW) is composed of a median metallic strip separated by two narrow slits from an infinite ground plane. The characteristic dimensions of a CPW are the central strip width Wand the width of the slots s. The structure is obviously symmetrical along a vertical plane running in the middle of the central strip (as shown in Fig. 2) [9]. Fig. 2: Side view of a Coplanar Waveguide [9] A CPW can be quasi-statically analyzed by the use of conformal mappings. Since the substrate has a finite thickness h, to carry out the analysis of this conformation, a preliminary conformal mapping transforms the finite thickness dielectric into an infinite thickness. In this analysis, the CPW conductors and the dielectric substrates are assumed to have perfect conductivity and relative permittivity respectively. Hence the structure is considered to be loss less. Further the dielectric substrate material is considered to be isotropic. In this analysis, expressions for determining εreff and Z0 using conformal mapping techniques are presented. The assumptions made are that the conductor thickness t is negligible and magnetic walls are present along all the dielectric boundaries including the CPW slots. The CPW is then divided into several partial regions and the electric field is assumed to exist only in that partial region. In this manner the capacitance of each partial region is determined separately. The total capacitance (CCPW) is then the sum of the partial capacitances. In this case the partial capacitances are capacitance due to substrate (C1) and capacitance due to air (Cair). Therefore, the total capacitance can be given as [9]: International Conference on Communication Systems (ICCS-2013) B K Birla Institute of Engineering & Technology (BKBIET), Pilani, India October 18-20, 2013 Page 97
  • 4. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME Where C1 and Cair is given as [9]: and (2) Hence the total Capacitance as given in equation 1 can be written as: Now using above capacitances values, effective dielectric constant can be given as [9]: Here K(k) and K’(k) represents the complete elliptical integral of the first kind and it’s complement, and and (5) The impedance of such a coplanar transmission line is given as [9]: Where, c is the velocity of light in free space. The guided wavelength λg for a coplanar waveguide is given as: Using above equation for guided wavelength, dimension of the coplanar patch design are calculated. The length of the coplanar patch is approximately taken as λ g/4 whereas the width of the patch is taken such that the length and width summation of the patch dimensions should not exceed λg. Here in this design the width is approximately taken as λ g/2. And the ground dimension around the patch is taken 5 times the dimension of the patch. III. DESIGN AND SIMULATION The coplanar patch antenna is designed on Rogers/RT duroid 5880 substrate with dielectric constant, εr = 2.2, dielectric loss tangent = 0.0009 and thickness of the substrate is 0.508mm. The strip gap (s) is taken as 0.2mm and width (W) of the coplanar waveguide feed is 1.252mm. The antenna is designed for an operating frequency of 10GHz. Using these design parameters International Conference on Communication Systems (ICCS-2013) B K Birla Institute of Engineering & Technology (BKBIET), Pilani, India October 18-20, 2013 Page 98
  • 5. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME and equation 1 to 7, the length and width of the coplanar patch is calculated as 4.3mm and 10.5mm respectively. The coplanar patch antenna modeled in HFSS software is shown in Fig. 3. Fig.3:Model of Coplanar Patch Antenna in HFSS software A microstrip patch antenna is designed for the same operating frequency and on the same substrate as that of the coplanar patch antenna so as to analyze the differences between a microstrip and coplanar patch antenna. The patch length and width calculated for the microstrip patch antenna are 9.24015mm and 11.9mm respectively. The feed width for microstrip patch antenna is 1.6mm. The Microstrip Patch Antenna modeled in HFSS software is shown in Fig. 4. Fig. 4: Model of Microstrip Patch Antenna in HFSS Software. IV. RESULTS AND DISCUSSION Full wave electromagnetic simulation of both the antenna models in HFSS software yield various antenna parameters such as return loss, radiation efficiency, directivity, bandwidth etc. Both the designs are simulated at 10GHz operating frequency. However, coplanar patch antenna model has a resonance frequency at 10.0557GHz and has a return loss of -32.2009dB, International Conference on Communication Systems (ICCS-2013) B K Birla Institute of Engineering & Technology (BKBIET), Pilani, India October 18-20, 2013 Page 99
  • 6. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME whereas microstrip patch antenna has resonance frequency at 9.9585GHz and return loss value of -40dB. The ‫׀‬S11‫ ׀‬plots with respect to frequency for both the design are shown in Fig. 5. Fig. 5: Simulation Results of ‫׀‬S11‫ ׀‬plot versus frequency The radiation efficiency obtained for coplanar antenna is 97.84% and that for a microstrip patch antenna is 88.63% i.e. 10.5% more than the efficiency of the microstrip patch antenna. Similarly, coplanar patch antenna has an impedance bandwidth of 17.75% (i.e. 1.785GHz) whereas that for a microstrip patch antenna is approximately 2%. However microstrip patch antenna has 5.35dB directivity whereas coplanar patch antenna has 2.79dB directivity value. The reason for the low directivity in case of coplanar patch antenna is that it has patch and ground on the same plane so the electric field below the patch also form a lobe on the other side of the patch forming a broadside pattern, whereas in case of microstrip patch the fields below the patch are shorted by the lower ground making a single lobe in one direction above the patch forming a unidirectional pattern. The radiation pattern plot for coplanar and microstrip patch antenna are shown in Fig. 6. (a) (b) Fig. 6: Radiation Pattern of: (a) Coplanar Patch Antenna; (b) Microstrip Patch Antenna. International Conference on Communication Systems (ICCS-2013) B K Birla Institute of Engineering & Technology (BKBIET), Pilani, India October 18-20, 2013 Page 100
  • 7. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME V. CONCLUSION Full wave EM simulation of coplanar and microstrip patch antenna models shows that for same operating frequency and same substrate coplanar patch antenna gives wider impedance bandwidth and high radiation efficiency than microstrip patch antenna. An impedance bandwidth of 17.75% and a radiation efficiency of 97.84% are achieved in case of a coplanar patch antenna. However, the directivity is higher in case of microstrip patch antenna and also the size of the microstrip patch antenna is smaller than the coplanar patch antenna. But the directivity of the coplanar patch antenna can be improved by providing another conductor (or ground) below the substrate; such designs are called as Conductor Backed Coplanar Patch Antennas. These type of antennas have unidirectional pattern and have better directivity then coplanar patch antenna. Due to its high radiation efficiency and wide bandwidth it can be applicable in satellite transponders and in military RADAR and satellite communication systems. VI. ACKNOWLEDGEMENT Authors are thankful for financial support obtained from CSIR India. REFERENCES [1]Ramesh Garg, PrakashBhartia, InderBahl and ApisakIttipiboon, “Microstrip Design Antenna Handbook”, Artech House, Boston, London. [2]Constantine A. Balanis, “Antenna Theory: Analysis and Design”, Third Edition, John Wiley & Sons, Inc., Publication, New Jersey. [3]D. Patel, and F. Raval, “Design and cavity model analysis of inset feed rectangular microstrip patch antenna”, Published in IEEE Conference NUiCONE-2012, 06-08 December 2012, India. [4]M. M. Abd- Elrazzak, and Ibrahim S. Al Nomay, “A Design of a Circular Microstrip Patch Antenna for Bluetooth and HIPERLAN Applications”, 9th Asia Pasific Conference on Communications 2003, Vol.3, 21-24 September 2003. [5]J. P. Damiano, J. M. Ribero, and R. Staraj, “Original Simple and Accurate Model for Elliptical Microstrip Antennas”, Electronic Letters, Vol. 31, 1995, PP. 1023-1024. [6]P. J. Soh, M. K. A. Rahim, A. Asrokin, and M. Z. A. Abdul Aziz, “Comparative Radiation Performance of Different Feeding Techniques for a Microstrip Patch Antenna”, 2005 Asia Pacific Conference on Applied Electromagnetic Proceedings, 20-21 December 2005, Johor, Malaysia. [7]Amit A. Deshmukh, K. P. Ray, and AmeyaKadam, “Proximity fed Circular Microstrip Antennas”, Applied Electromagnetics Conference, (AEMC), 2011, IEEE Conference Proceedings, 18-22 December 2011, Kolkata, India. [8]Horng-Dean Chen, Chow-Yen-Desmond, Jun-Yi Wu, and Tsung-Wen Chiu, “Broadband High Gain Microstrip Array Antennas for WiMAX Base Station”, IEEE Transaction on Antenna and Propagation, Vol.60, No.8, August 2012. [9]Rainee N. Simons, “Coplanar Waveguide Circuits, Components, and Systems”, John Wiley & Sons, Inc., Publication, New York. [10]Paul L. Chin, Atef Z. Elsherbeni, and Charles E. Smith, “Characteristics of Coplanar Bow Tie Patch Antennas”, Antennas and Propagation Society International Symposium-2002, Vol.4, 1621 June 2002, San Antonio, Texas. International Conference on Communication Systems (ICCS-2013) B K Birla Institute of Engineering & Technology (BKBIET), Pilani, India October 18-20, 2013 Page 101
  • 8. International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976 – 6464(Print), ISSN 0976 – 6472(Online), Special Issue (November, 2013), © IAEME [11]Rohith K. Raj, Manoj Joseph, C. K. Aanandan, K. Vasudevan, and P. Mohanan, “A New Compact Microstrip Fed Dual Band Coplanar Antenna for WLAN Applications”, IEEE Transactions on Antennas and Propagation, Vol. 54, N0. 12, December 2006. [12]Atef Z. Elsherbeni, Abdelnasser A. Eldek, Brad N. Baker, Charles E. Smith, and Kai-Fong Lee, “Wideband Coplanar Patch Slot Antennas for RADAR Applications”, Antennas and Propagation Society International Symposium-2002, Vol.4, 16-21 June 2002, San Antonio, Texas. [13] David B. Davidson, “Computational Electromagnetics for RF and Microwave Engineering”, Cambridge University Press 2005, New York. BIOGRAPHY Avanish Bhadauria received the B.Sc (Hons). degree in physics from Dayalbagh Educational Institute, Agra, M.Sc. degree in Electronics from Jiwaji University, Gwalior and the PhD in Microwave Photonics from University of Delhi in 1996, 1998 and 2005, respectively. During his PhD he has been awarded Junior Research and Senior Research Fellowship by CSIR. Currently, he is a scientist in CSIR- Central Electronics Engineering Research Institute (CEERI), Pilani (Rajasthan) since 2005. His interests include RF MEMS, RF reconfigurable antennae modelling of interconnect in High speed VLSI, Optoelectronic, THz electronics and microwave-photonic component design. He is member of IEEE, MTT, Optical Society of America, Fellow member of Optical Society of India and Life member of Semiconductor Society of India. He is also in an editorial board of International Journal of Advancement of Technology and International Journal of Advances in Engineering & Technology. Jalaj Sharma received his B.E. degree in Electronics and Communication Engineering from Samrat Ashok Technological Institute, Vidisha and M.E. degree in Microwave Engineering from Jabalpur Engineering College, Jabalpur in 2009 and 2012 respectively. Presently, he is working as a Project Fellow in CSIR- Central Electronics Engineering Research Institute (CEERI), Pilani (Rajasthan). His areas of interest include RF MEMS based reconfigurable antenna and RF circuits. Arvind Singh Jadon received his B.Tech (Hons.) degree in Electronics and Communication Engineering from B K Birla Institute of Engineering & Technology, Pilani. Presently, he is working as a Lecturer in B K Birla Institute OF Engineering & Technology (BKBIET), Pilani. His areas of interest include RF MEMS based reconfigurable antennae. Ajay Prajapat received his B.Tech degree in Electronics and Communication Engineering from B K Birla Institute of Engineering & Technology, Pilani. Presently, he is working as a quality engineer in autopal industries ltd. Jaipur. International Conference on Communication Systems (ICCS-2013) B K Birla Institute of Engineering & Technology (BKBIET), Pilani, India October 18-20, 2013 Page 102