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Antenna miniaturization techniques
Dec 21, 2012
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1. International INTERNATIONAL JOURNALEngineering & Technology (IJECET), ISSN 0976 Journal of Electronics and Communication OF ELECTRONICS AND COMMUNICATION ENGINEERING & TECHNOLOGY (IJECET)– 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 3, October- December (2012), © IAEMEISSN 0976 – 6464(Print)ISSN 0976 – 6472(Online)Volume 3, Issue 3, October- December (2012), pp. 197-201 IJECET© IAEME: www.iaeme.com/ijecet.aspJournal Impact Factor (2012): 3.5930 (Calculated by GISI) ©IAEMEwww.jifactor.com ANTENNA MINIATURIZATION TECHNIQUES FOR WIRELESS APPLICATIONS Rajendra R. Patil1, Vani R. M2, 3P.V. Hunagund 1 Dept. of E&CE, Appa Institute of Engineering & Technology, Gulbarga-585103, Karnataka, India. Email- firstname.lastname@example.org University Science Instrumentation Centre, Gulbarga University, Gulbarga-585106 Karnataka, India. Emailemail@example.com 3 Dept. of Applied Electronics, Gulbarga University, Gulbarga-585106, Karnataka, India Emailfirstname.lastname@example.orgABSTRACTThis paper reports simulated analysis of small planar antennas (Microstrip Patch Antennas)miniaturization using different methodologies. The effect of miniaturization on antennaparameters like resonance frequency, return loss, radiation efficiency, and bandwidth arediscussed.Keywords: antenna miniaturization, microstrip patch antenna, magneto-dielectrics1. INTRODUCTIONAntenna is a device designed for radiating or receiving radio waves . The microstripantennas also referred to as microstrip patch antennas (MSA) have several advantages likesmall size, light weight, low cost, low volume and easy to fabricate using printed circuittechnology over conventional microwave antennas and therefore are widely used in manypractical applications like aircraft, spacecraft, satellite, missile, mobile, GPS, RFID, Wi-Maxand Radar etc. The radiating elements and the feed lines are usually photo etched on thedielectric substrate. MSAs suffer from disadvantages like low radiation efficiency, low gain,high Q, narrow impedance bandwidth etc.Wireless systems and their size reduction (miniaturization) has become a vital issue now a day.The demand for commercial and military mobile wireless communication system is on the rise.Smaller physical size, higher radiation efficiency, and wider bandwidth are three desiredcharacteristics of antennas for communication systems. Some approaches for antennaminiaturization are introduction of slots, slits, short meandering and novel geometries likefractals or by using higher dielectrics constant. However, all the above techniques results inreactive loading of the antenna and hence results in higher Q and reduced bandwidth, makingthem unsuitable for most of the applications [2-3]. To achieve wide bandwidth it is a generalmethod using of thick dielectric substrate. However, it decreases the antenna gain by increasingstoring of energy within substrate. Recently, magneto-dielectric substrate with permittivity andpermeability higher than one has been proposed . This approach uses nanotechnology toolsand techniques for the development of magneto-dielectric substrates  . This paperpresents simulation analysis of antenna miniaturization using (a) slots in the patch of theantenna (uses simple fabrication), (b) loading high value permittivity in the substrate of theantenna, and (c) loading magneto-dielectrics in the substrate of the antenna (permittivity, 197
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976– 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 3, October- December (2012), © IAEME Octoberpermeability values greater than one are known with negligible material loss). Magneto-dielectrics property in the material can be developed by nano composite materials like Nickel- NickelCobalt-Zink Ferrites, Copper-Cobalt Cobalt-Zink Ferrites, Cobalt-silica-BCB etc., as substrate BCBmaterial [5-7]. These types of material development make use of nanotechnology.2. BASE ANTENNA DESIGN AND SIMULATIONFor antenna miniaturization, aperture coupled microstrip patch antenna (ACMSA) is preferredand selected as it offers greater design flexibility. The base antenna ACMSA is designed and desigsimulated at 2.2GHz for FR4 substrate with a thickness of 1.6 mm and dielectric constant of 42.54, illustrated in fig.1 (a) and 1(b) . In ACMSA, the field is coupled from the microstrip (b) ].line feed to the radiating patch through an electrically small aperture or slot cut in the gro groundplane. The coupling aperture is usually centered under the patch, providing low cross- crosspolarization due to the symmetry. The shape, size, and location of the aperture decide theamount of coupling from the fed line to the patch. The antenna design was undertaken through undertakensimulations using the IE3D software version 14.65. IE3D is a full wave EM solver . It full-wavesolves the Maxwell Equations, which govern the macro electromagnetic phenomenon. There isno much assumption involved except the numerical nature of the method. Therefore, the Therefsolution is extremely accurate. The simulated result for base antenna is listed in Table 1. (a) (b) (c) (d) (e)Figure 1. (a) ACMSA geometry (b) simulated geometry (c) electric current distribution (d)magnetic current distribution (e) both electric and magnetic current distribution.3. ANTENNA MINIATURIZATION BY USE OF SLOTS IN THE PATCHFig. 2(a) shows the antenna structure with a rectangular patch and two rectangular slots on )either side in it. The shape of this antenna is similar of the one in fig.1 (a). However with .changing the dimensions in the patch, the effect of slots on the properties of the antenna havebeen changed and listed in Table 1. It can be seen that by introducing two slots on either side of 1. ethe patch there is a lower frequency shift and hence miniaturization of 11.56 percent. However percentthere is a decrease in return loss, bandwidth and radiation efficiency The simulated result is efficiency.listed in table 1. µr = 1, εr = 2.54 (a) (b) (b (c) (d)Figure 2. (a) ACMSA simulated geometry with slots (b) electric current distribution (c)magnetic current distribution (d) both electric and magnetic current distribution. 198
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976– 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 3, October December (2012), © IAEME October-Figure 2(a) shows simulated ACMSA geometry with two slots of size 3mm x 24mm on eitherside in the conducting patch, and current distributions. Across slot we have magnetic currentwhich couples feed line and centre of the patch at which electric field is zero. However there is Howeva maximum current distribution on either side of the patch. Also we can notice increase in pathof vector current compared with current distribution in base antenna. The presence of slotsincreases current path length which gives lower shift in resonant frequency and decrease inefficiency and bandwidth.4. ANTENNA MINIATURIZATION BY USE OF HIGH PERMITTIVITYDIELECTRIC MATERIALSThe uses of high permittivity substrate allow reducing the electrical size of the antenna throughthe reduction of the effective wavelength ( λ ), and bandwidth related to permittivity ( ε ) and he ,permeability ( µ ) are given by the equations λ=λ o / ε r µ r ; BW ≈ µ / ε (1)where λ o is free space wavelength. As it can be seen in the denominator, with µ r =1 , the antennaminiaturization is achieved by controlling controlling/varying only ε r . For different values of ε r (forexample: 3, 4, 5), the antenna is simulated for miniaturization. The simulated parameters are helisted in Table 1. From the table it is clear that the use of high permittivity dielectric materials .offer an interesting size reduction (by slowing the confined wave inside the substrate), but the subsbandwidth and radiation efficiency is significantly reduced due to field confinement around thehigh permittivity region. Fig. 3(b)- illustrates simulated results. -(d)From the equations of the electrical wavelength and bandwidth, high permittivity or high permittivitypermeability materials are good at reduction of size but these causes decreasing of bandwidth bandwidtor increasing of loss tangent respectively. Therefore, the use of high permittivity dielectricmaterial is often restricted to antennas operating at a single narrow band application like GPSand Bluetooth. µ=1, εr >2.54 r (a) (b) (c) (d)Figure 3. (a) ACMSA with high dielectrics (b) Return loss Vs Frequency (c) 2D Radiation .pattern (d) Efficiency Vs frequency4. ANTENNA MINIATURIZATION BY USE OF MAGNETO-DIELECTRICS ZATION MAGNETO DIELECTRICSThe limitation in use of dielectric material with high permittivity can be overcome by magneto- magnetodielectric materials. In spite of using material with high permittivity, the same miniaturization 199
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976– 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 3, October December (2012), © IAEME October-can be obtained by using materials with moderate permittivity and permeability i.e. ε, µ > 1 , asshown in fig. 4. Magneto-dielectric material provides control of both permittivity and dielectricpermeability, as it can be seen in the denominator of equation (1). The base antenna issimulated for different values of ε r and µ r where ε r /µ r > 1, ε r /µ r =1, and ε r /µ r <1. The resultsare listed in table 1. From the simulation results we could find that use of magneto . magneto-dielectricmaterial reduces the magnetic and electric imbalance, which enhances the system bandwidth byincreasing the amount of magnetic energy storage for a pure dielectric is capacitive. In table 1, dielectricfor ε r /µ r =1 the impedance between dielectric and surrounding free space is much reduced,hence bandwidth reaches maximum value. This is the advantage of magneto dielectric. For magneto-dielectric.ε r /µ r <1 it is seen that when permeability increases and permittivity decreases, the ability ofstrong energy inside the substrate is less and so the value of radiation resistance is higher andhence the radiation efficiency increases. Fig.4(b)-(d) shows simulated results for magneto- magnetodielectric loaded antenna. The bold data in the table indicates relative comparison between highpermittivity loaded and magneto-dielectric loaded antennas. dielectricε, µ > 1 ε r = µ r =1.74 (a) (b) (c) (d)Figure 4.(a) ACMSA with magneto dielectrics (b) Return loss Vs Frequency (c) 2D Radiation magneto-dielectricspattern (d) Efficiency Vs frequencyTable 1. Simulated parameters for base antenna, antenna with slots, antenna with dielectric atedconstant of high permittivity, and antenna with magneto magneto-dielectrics. Dielectric with High With Magneto-Dielectric : µ r × ε r = 3 Dielectric permittivity, µ r =1 Parameters εr εr >1 <1 Base εr εr µr εr µr With ε r =4 =1 Antenn µr slots =3 =5 a 2.12 1.58 0.75 0.48 Frequency (GHz) 2.2 1.95 2 1.77 1.6 2 1.77 2 2 2 Return loss (dB) 18.4 12 14.5 14.2 9.1 14.4 12.5 23 19.2 13.4Bandwidth (MHz) 24 7 18.0 11.4 0 23.7 14.7 30 29.9 28.2 Radiation 85 76.4 85 82 79.3 87 84 85.8 85.6 83.7 efficiency (%) Reduction in size -- 11.5 6.8 19.8 27.6 6.8 19.8 6.8 6.8 6.8 (%) 200
International Journal of Electronics and Communication Engineering & Technology (IJECET), ISSN 0976– 6464(Print), ISSN 0976 – 6472(Online) Volume 3, Issue 3, October- December (2012), © IAEMECONCLUSIONThis paper has presented some of the techniques and approaches that are commonly used forplanar antennas miniaturization using IE3D 14.65 simulation software. By varying bothpermittivity and permeability of the substrate, good bandwidth and radiation efficiency can beobtained in addition to antenna miniaturization. The antenna with magneto-dielectric materialhas better bandwidth than dielectric antenna in the same size. It also presents opportunities andchallenges that new materials (magneto-dielectrics) pose for the design of small antennas.ACKNOWLEDGEMENTWe thank the authorities of UGC, Govt. of India, New Delhi, for sanctioning IE3D 14.65simulation software to Gulbarga University, Gulbarga. Author R.R.P would like to conveysincere thanks to President, Principal, and Dean of Appa Institute of Engineering andTechnology, Gulbarga for constant support and encouragement for research work.REFERENCES Balanis, C. A., “Antenna Theory Analysis and Design”. John Wiley & Sons, New Delhi, India, 2009. Lo, T.K., Ho C.O., Hwang Y., Lam, E. K. W., and Lee, B., “Miniature Aperture- Coupled Microstrip Antenna of very high Permittivity”. Electronics Letters, Vol. 33, 1997, pp: 9–10. Hwang, Y., Zhang, Y.P., Zheng, G.X., Lo, T.K.C., “Planar Inverted F Antenna Loaded with high Permittivity Material”, Electronics Letters, Vol. 31, no. 20, 1995, pp: 1710–1712. Lee J., Heo J., and Lee J., “Design of Small Antennas for Mobile Handsets using Magneto-Dielectric Material”, IEEE Trans. Antennas Propag., 60, 2080-2084, 2012. The Inframat website (2005). “Magnetic Nanocomposite Paste: An Ideal High- µ r , k and nanomaterial for Embedded Inductors in High Frequency Electronic Applications”, [Online]. Available: http://www.inframat.com/press/Georgia.pdf Prasath S.D.R., et al., “Miniaturization of patch antennas using magneto-dielectric Materials”, A Workshop on Advanced Antenna Technology, Indian Antenna Week., pp.1- 4, May 31-June 4, 2010. David M. Pozar, “A Reciprocity Method of Analysis for Printed Slot and Slot-Coupled Microstrip Antennas”, IEEE Trans. Antenna Propag, Vol. AP-34, No 12, p.p. 1439-1446, December 1986. IE3D version 14.65: Zeland Software Inc., USA, 2010. 201