Wideband Dual Segment Rectangular Dielectric Resonator Antenna Terminate in Bio-Media

Wideband Dual Segment Rectangular Dielectric Resonator Antenna Terminate in Bio-Media Ravi Kumar Gangwar, S. P. Singh and D. Kumar Abstract In this paper a wideband dual segment rectangular dielectric resonator antenna (RDRA) designed for WiMAX band (3.2 GHz and 5.5 GHz) and power absorption in a homogenous biomedium (muscle layer) in proximity with the proposed antenna are described. The simulation results for the characteristics of the proposed antenna and the specific absorption rate (SAR) distribution in the muscle layer are discussed. Keywords Dual segment RDRA, Muscle layer, SAR, WiMAX Band. D I. INTRODUCTION IELECTRIC resonator antennas (DRAs) have attracted the attention of several investigators due to their high radiation efficiency, flexible feed arrangement, simple geometry, structure, small size low profile, light weight, low cost, a wide range of material dielectric constant, ease of excitation and easily controlled characteristics [1-4]. DRAs are available in various basic classical shapes such as rectangular, cylindrical, spherical and hemispherical geometries. Rectangular DRAs can be designed with greater flexibility since two of the three of its dimensions can be varied independently for a fixed resonant frequency and known dielectric constant of the material [5]. The availability of one degree of freedom more than cylindrical and spherical DRAs can be used to control the bandwidth of the antenna. The techniques used to improve the bandwidth of the DRAs include changing the aspect ratio of DRA, employing multisegments and stacked DRAs and by varying the dielectric constant of DRA material. For wider-band applications, DRAs having lower dielectric constant values are preferred. This results in week coupling. Multi-segment DRAs can be used to overcome this problem [6-7]. Manuscript received April 7, 2010. First author, R. K. Gangwar wishes to express thanks to the Dept. of Electronics Engineering, Institute of Technology, Banaras Hindu University, Varanasi and University Grant Commission, New Delhi for awarding Senior Research Fellowship. Ravi Kumar Gangwar is with the Department of Electronics Engineering, Institute of Technology, Banaras Hindu University, Varanasi, India (phone: +91-542-6701258; fax:+91-542-2366758; email: ravi.gangwar.ece07@ itbhu.ac.in). S. P. Singh, is with Department of Electronics Engineering, Institute of Technology, Banaras Hindu University, Varanasi, India (e-mail: spsingh.ece@itbhu.ac.in). D. Kumar is with Department of Ceramic Engineering, Institute of Technology, Banaras Hindu University, Varanasi, India (e-mail: devendra.cer@itbhu.ac.in). With the expansion of current use and anticipated further increases in the use of personal communication devices and wireless portable devices, interest in the study of interactions between antennas and human body is growing. These activities are motivated by two factors. First one stems from the need to evaluate the performance of antenna in presence of bio-layers and second one is concerned with the rate of electromagnetic energy absorption, known as specific absorption rate (SAR) [8]. A portion of the body of a person using wireless portable device is exposed to electromagnetic waves radiated from the device antenna. The human body being lossy absorbs certain amount of electromagnetic radiation generated from the device. Therefore, it is of interest to evaluate the power absorbed /specific absorption rate (SAR) in the body tissues due to wireless device antenna radiating electromagnetic waves [9]. The electric field induced and hence SAR within the human body depends on several factors including the strength and frequency of the external field, the shape, size and electrical characteristics of the body tissues and the orientation of the body in relation to the external field. In this paper, the design aspects and characteristics of a dual segment rectangular dielectric resonator antenna, which is fed by a 50 Ω coaxial probe for WiMAX band (3.2 GHz and 5.5 GHz), are presented. The specific absorption rate distribution in a homogenous bio-medium (muscle layer) in proximity with the proposed antenna obtained through simulation using CST Microwave studio software is also reported. II. ANTENNA GEOMETRY The dual segment DRA consists of lower segment made from thin teflon sheet with dielectric constant and an upper segment of alumina block with as shown in Fig. 1. The dual segment DRA is placed on a ground plane of size 40 15 4 mm 3. The lower and upper segments of the DRA have dimensions of a b h 2 and a b h 1 respectively. The DRA is excited by a 50 Ω coaxial probe of outer radius 2 mm and inner radius 0.6 mm. The height of the probe is determined through simulation using CST Microwave Studio software. A metallic plate of negligible thickness fully covers the side of DRA just opposite the side where feed is located. The design parameters of the antenna are a = 20 mm, b = 12 mm, h 1 = 3 mm, h 2 = 10 mm and probe height = 11.6 mm. ISSN: 1792-4316 64 ISBN: 978-960-474-207-3

Metallic plate It is worth mentioning that the input resistance at resonant frequency of the RDRA is found to be 50.42 Ω providing very good impedance match to 50 Ω coaxial feeder. Fig. 1 Geometry of dual segment rectangular dielectric resonator antenna III. RESULTS AND DISCUSSION A. Near field distribution The simulation study of electric field distribution in the proposed dual segment wideband RDRA has been carried out at 5.156 GHz using CST Microwave Studio software. When proposed antenna is excited using a 50 Ω coaxial probe as shown in Fig. 1, the electric field distribution in x-z and y-z planes look like those shown in Fig. 2. It is apparent from Fig. 2 that the coaxial probe excites dominant mode fields in the structure. Fig. 3 Return loss performance of dual segment rectangular dielectric resonator antenna Fig. 4 Input impedance curve of dual segment rectangular dielectric resonator antenna Fig. 2 Electric field distribution in dual segment rectangular dielectric resonator antenna B. Return loss and input impedance characteristics The simulation study of return loss and input impedance vs. frequency characteristics for the proposed dual segment RDRA has been carried out using CST Microwave Studio software. The return loss and input impedance vs. frequency curves of the proposed antenna has been presented in Figs. 3 and 4. From Fig. 3 the resonant frequency, operating frequency range and the percentage bandwidth of the proposed RDRA are extracted. The resonant frequency, operating frequency range and the percentage bandwidth are found to be 5.156 GHz, 3.04-5.65 GHz and 50.62% respectively. The frequency at which total reactance of the structure goes down to zero is lower than that at which resistance becomes maximum. This happens due to finite inductance offered by the coaxial probe feed. Fig. 5 shows the return loss vs. frequency characteristics of RDRA for different length of the lower segment keeping total antenna height constant at 13 mm. From Fig. 5 it can be seen that the resonant frequency of the antenna increases with increase in length of the lower segment. Fig. 5 Variation of length of dielectric segment with Return loss vs. frequency curves of dual segment rectangular dielectric resonator antenna ISSN: 1792-4316 65 ISBN: 978-960-474-207-3

C. Far field performance The far field pattern of the proposed dual segment RDRA at resonant frequency of 5.156 GHz were obtained through simulation using CST Microwave Studio software. The simulated radiation patterns of the proposed antenna in x-z, y- z and x-y planes and in three dimensions are shown in Figs. 6 (a), (b), (c) and (d) respectively. The 3 db angular width, side lobe level, main lobe magnitude and the direction of main lobe are extracted from Fig. 6. The values of extracted parameters in the order they are just mentioned are found to be 37.4 0, - 6.2 db, 7.3 db and 90 0 for x-z plane. The corresponding values for y-z plane are 37.4 0, nil, 7.3 db and 90 0. The radiation pattern of the antenna in x-y plane is omni-directional. From Fig. 6 it can be also observed that presence of metallic plate significantly reduces the power radiated towards back side of the plate. The gain, directivity and total efficiency of the antenna are found to be 7.696 db, 7.710 dbi and 99.69% respectively. The gain and directivity of the antenna are found to match the characteristics of wideband antenna used for WiMAX applications [10-11]. (b) (c) (a) (d) Fig. 6 Far field performance of dual segment rectangular DRA (a) in x-z plane (b) in y-z plane (c) in x-y plane (d) 3-D pattern D. SAR evaluation The origin is selected on the top surface of ground plane coinciding with the central line of dual segment RDRA as shown in Fig. 7. The values of SAR (10g) in muscle layer located at a distance of 1.5 mm from the side surface of proposed antenna as shown in Fig. 7 at the resonant frequency of 5.165 GHz and at another frequency of 3.31 GHz were obtained through simulation. The mass density of muscle layer available in literature is 1050 Kg/m 3 [12]. The complex permittivity, electrical conductivity of muscle layer compiled from the available literature [13] are 49.399, 4.2156 S/m at 5.156 GHz and 51.678, 2.3944 S/m at 3.31 GHz respectively. The simulated SAR (10g) distributions in the muscle layer along x, y and z directions at 5.165 and 3.31 GHz for proposed antenna are shown in Fig. 8. The four parameters of importance for obtaining the volume of the tissue absorbing significant amount of power ISSN: 1792-4316 66 ISBN: 978-960-474-207-3

are SAR, power loss density, effective field size (EFS) and penetration depth. The power loss density is obtained by multiplying point SAR with the mass density of the tissue. The EFS is defined as the area that is enclosed within the 50 % SAR contour inside the tissue. The penetration depth is the depth at which SAR becomes 1/ e 2 of its value at the surface [12]. The maximum SAR (10g), maximum power loss density, EFS and penetration depth in the bio-medium due to the dual segment RDRA extracted from Fig. 8 are shown in Table 2. From Table 2 it can be observed that maximum value of SAR (10g), power loss density, effective field size (EFS) and penetration depth values are higher at the lower frequency of 3.31 GHz. These results are in conformity with those given in reference [14]. (b) Fig. 7 Geometry of dual segment DRA with muscle layer TABLE 2 SAR PERFORMANCE OF DUAL SEGMENT RDRA IN MUSCLE LAYER Parameters At 3.31 GHz At 5.156 GHz Maximum SAR (10g) 19.4886 W/Kg 8.05644 W/Kg Power Loss Density 416074 W/m 3 138996 W/m 3 Effective Field Size 22.849 26.8 mm 2 21.998 25.478 mm 2 Penetration Depth 17.8 mm 15.09 mm (c) Fig. 8 SAR (10g) variation in muscle layer due Dual segment RDRA (a) with x-axis (b) with y-axis (c) with z-axis IV. CONCLUSION The dual segment rectangular DRA, which provides wide bandwidth in WiMAX bands has been proposed in this paper. The radiation characteristics of the proposed antenna and SAR distributions in a bio-medium in proximity with the antenna are evaluated through simulation studies using CST Microwave Studio software. From the study it is inferred that the bandwidth of the proposed antenna is found to be 50.25% which covers 3.2 GHz and 5.5 GHz WiMAX band. The volume of the bio-layer kept near the antenna absorbs more power at lower frequency of WiMAX band. The results presented here may find potential application in wireless communication field for designing a wideband antenna and evaluating the power absorption in bio-layers due to the antenna. (a) REFERENCES [1] R.K. Mongia and P. Bhartia, DRA- A review and general design relation for resonant frequency and bandwidth, International journal of Microwave and Millimeter wave computer aided engineering, vol.4, No.3, pp 230-247, 1994. [2] Ittipiboon and R. K. Mongia, Theoretical and experimental investigations on rectangular dielectric resonator antennas, IEEE Transactions on Antennas and Propagation, Vol. 45, No. 9, pp. 1348 1356, Sept. 1997. [3] P.Rezaei, M.Hakkak and K.Forooaghi, Design of wideband dielectric resonator antenna with a two segment structure, Progress in Electromagnetics Research, PIER 66, pp. 111 124, 2006. [4] Darko Kajfez and A. A. Kishk, Dielectric Resonator Antenna- Possible Candidate for Adaptive Antenna Arrays, Proceedings VITEL 2002, International Symposium on Telecommunications, Next Generation Networks and Beyond, Portoroz, Slovenia, May 13-14, 2002. [5] M. Saed and R. Yadla, Microstrip-fed low profile and compact dielectric resonator antennas, Progress In Electromagnetics Research, PIER 56, pp.151 162, 2006. ISSN: 1792-4316 67 ISBN: 978-960-474-207-3

[6] Aldo Petosa, Dielectric Resonator Antennas Handbook, Artech House, Bostonk, london, 2007. [7] Yuehe Ge, K.P. Esselle "A dielectric resonator antenna for UWB applications," IEEE International Symposium on Antennas and Propagation Society, pp.1-4, 1-5 June 2009. [8] Michal Okoniewski, Maria A. Stuchly, A study of the handset antenna and human body interaction, IEEE Trans. on Microwave Theory and Techniques, vol. 44, no. 10, pp.1855-1864, 1996. [9] Pradier, D. Lautru, M. F. Wong, V. H. Fouad and J. Wiart, Rigorous evolution of specific absorption rate (SAR) induced in a multilayer biological structure, European Microwave Conference, Vol. 3, 2005. [10] Ravi Kumar Gangwar, S.P. Singh and D. Kumar, A Modified Fractal Rectangular Curve Dielectric Resonator Antenna for WiMAX Application, Progress in Electromagnetic Research C, Vol. 12, 37-51, 2010. [11] Tze-Hsuan Chang and Jean-Fu Kiang, Sectorial-beam dielectric resonator antenna for WIMAX with bent ground plane, IEEE Transactions on Antennas and Propagation, Vol. 57, No. 2, pp. 563 567, Feb. 2009. [12] M. A. Ebrahimi-Ganjeh, Study of Water Bolus Effect on SAR Penetration Depth and Effective Field Size for Local Hyperthermia, Progress in Electromagnetics Research, vol. 66, pp.111 124, 2006. [13] An Internet resource for the calculation of the Dielectric properties of Body tissues in the frequency range 10Hz-100GHz. Italian national research council, institute for applied physics. http://niremf.ifac.cnr.it/tissprop/ [14] R. C. Gupta and S. P. Singh, Mutual Coupling Between Box-Horn Elements of a Phased Array Terminated in Three-layered Bio-Media, IEEE Trans. on Antennas and Propagation, Vol. 55, No. 8, pp. 2219 2227, August 2007. He is life member of Indian Ceramic Society, Materials Research Society of India, Indian Physics Teachers Association and Fellow of Indian Institute of Ceramics. Ravi Kumar Gangwar was born in Bareilly (Uttar Pradesh), India, in 1983. He received the B. Tech. degree in Electronics and Communication Engineering from U.P. Technical University, Lucknow, India, in 2006, and currently pursuing his Ph.D. degree in Electronics Engineering from the Institute of Technology, Banaras Hindu University (IT-BHU), Varanasi, India. He has worked as a Junior Research Fellow from April 01, 2007 to March 31, 2009 and now he is working as Senior Research Fellow in the Department of Electronics Engineering, IT-BHU, from April 01, 2009. He has authored or coauthored over 10 research papers in international/national journals/conference proceedings. His research interest includes dielectric resonator antenna, metamaterial and bio-electromagnetics. He is a reviewer of PIER international journal. S. P. Singh received the B.Sc. degree in Science, B. Tech. degree in Electronics Engineering, M. Tech. and Ph.D. degrees in Electronics Engineering (Microwave Engineering) from Banaras Hindu University (B.H.U.), Varanasi, India, in 1971, 1976, 1979 and 1989 respectively. He is currently a Professor and Coordinator of the Centre of Advanced Study, Department of Electronics Engineering, Institute of Technology, Banaras Hindu University. He has guided eight Ph.D. theses and 40 M. Tech. dissertation projects. He has authored or coauthored over 104 research papers in international/national journals and conference proceedings. His areas of current research and publications include bioelectromagnetics, microwave antennas and communication. Prof. Singh is a Senior Member of the Institute of Electrical and Electronics Engineers (IEEE), USA and a Life Fellow of the Institution of Electronics and Telecommunication Engineers (IETE), India. He is a reviewer for a few international journals. His biography has been included in the Marquis Who s Who in the World, 2007. Devendra Kumar completed his M. Tech. (1975) and Ph.D. (1981) from Indian Institute of Technology, Kanpur (India). Presently he is Professor of Glass Technology and Head, Deptt. of Ceramic Engineering. For the last 25 years he is deeply engaged in post graduate and under graduate teachings in Ceramic Engineering Technology. He served as Research Engineer in Advance Centre for Material Science, IIT, Kanpur during 1981 to 1984. His area of research is electronic ceramic and glass ceramics. He published more than 100 research papers and participated in several international and national conferences. ISSN: 1792-4316 68 ISBN: 978-960-474-207-3