In This paper, we propose a directive triangular EBG antenna. This approach is derived from using an EBG surface near to a triangular patch with two grilles. The antenna frequency chosen is the 2.45GHz. The directive antenna is simulated by using HFSS and Electrical model. This proposed antenna presents a very high directivity

Ferchichi, Abdelhak

Gharsallah, Ali

English

International Journal of Electronics and Telecommunications (Warsaw University of Technology)

INTL JOURNAL OF ELECTRONICS AND TELECOMMUNICATIONS, 2013, VOL. 59, NO. 2, PP. 125–130Manuscript received December 14, 2012; revised April, 2013. DOI: 10.2478/eletel-2013-0015A Circuit Model to a Directive Triangular EBGAntennaAbdelhak Ferchichi and Ali GharsallahAbstract—In This paper, we propose a directive triangularEBG antenna. This approach is derived from using an EBGsurface near to a triangular patch with two grilles. The antennafrequency chosen is the 2.45GHz. The directive antenna issimulated by using HFSS and Electrical model. This proposedantenna presents a very high directivity.Keywords—EBG antenna, directive antenna, lumped element,mushroomI. INTRODUCTIONNOWADAYS, the development of telecommunicationssystems creates new needs that existing antennas cannotmostly all satisfy. Indeed, they must be broadband, highgain multiband agile diagram, frequency agile, low cost andsmall. Besides, the antenna is used in all the recent wirelesscommunication systems. The satisfaction of these conditions,as well as towards solutions multifunction antennas requiregreater adaptability. For all this reasons, the developing ofa new structures of antennas consist the challenge of ourresearch laboratory. A structure that is worth considering isthe antenna EBG (Electromagnetic Band Gap) because of itspotential especially in terms of gain, since it can significantlyincrease the directivity of a primary source. The EBG antennais composed of a resonator formed between the ground planeand the material half-EBG (periodic arrangement of dielectricor metallic elements) placed above it. For this reason, EBGstructures and their applications in antennas have becomea new research field in the RF systems, [1]–[5].The use EBG antenna was essentially to eliminate somelimits in classical antenna such us:• The suppression of surfaces waves in antenna groundplane.• Design a simple profile antenna near to ground plane.• Increase gain and directivity of antenna.The main problem of this kind of antenna is the complexityof the geometry. This means that the conception step will bevery difficult and takes a lot of time. Besides, the absence ofanalytic model to control all the antenna parameters from thephysical parameters of the antenna. On the other hand, dueto long simulation time, it will be very difficult to analyzeantenna response when we modify some parameters like theexcitation, the geometry of metallic element, substrate, . . . [6].In order to simplify the EBG antenna conception step wemust use a simple and efficacy simulator. In many works, weuse the industrial simulator like HFSS, ADS and CST. AllA. Ferchichi and A. Gharsallah are with Unit of Research Cir-cuits and Electronics Systems High Frequency, Faculty of Science, Uni-versity El Manar, Tunis, Tunisia (e-mails: abdelhakferchichi@yahoo.fr;ali.gharsallah@gmail.com).those tools are based on numerical methods as the method ofmoments (MoM), finite element method (FEM), and the finitedifference time domain (FDTD) method, which have been welldeveloped over the years. The different methods are based onresolving Maxwell equation on their integral or differentialform.Y. R. Samii presents in [7] the advantages in using EBGstructure to improve the performance of microwave and opticalsystems. In [8], A. R. Weily et all, A. R.Wiekley uses an EBGstructure to increase the gain and bandwidth of a resonatorantenna; its proposed structure is excitated with a slot tech-nique feed. On the other hand, L. Qiu et all combines theuse of an EBG surface with a choke structure to amelioratethe isolation between the emitter and the receiver antenna, [9].For [10], W. Cao at all develop a novel EBG antenna based onusing an EBG structure near to a simple patch; their proposedantenna is characterized by a multi-frequency and dual modeaspect. Lastly, according to [11], M.Kim et all demonstratethat a vertical inductive bridge electromagnetic band gap (VIB-EBG) structure can be used as a miniaturization technique ofantenna structure dimension, then this last technique is veryuseful in stop band enhancement and wideband suppression.We propose in this work, a design of a new directivetriangular EBG antenna with a high directivity. In the firstsection, we described our design of EBG structure where weevaluate EBG parameter by using an electrical model. In thesecond Section, we developed our proposed directive antennaby placing the chosen EBG design near to a triangular antennain first structure and then we place two metallic grilles nearthe EBG triangular patch to increase the directivity. In thelast section, we conclude our work and we suggest someperspectives.II. THE EBG ELEMENTARY CELLULEEBG structures are usually realized by periodic arrangementof dielectric materials or/and metallic conductors. In general,they can be classified to three groups according to theirgeometric configuration.The complexity of this type of antenna makes the determi-nation of the size of these structures a very difficult operation.The studies on these antennas have shown that a study of theelementary cell of the metal blocks reflects the behavior of thenetwork blocks, [12]. At this stage, the electrical modelingis effective because from modeling the unit cell, we candetermine the geometric dimensions of the metal pad (Fig. 1).Several studies have examined this type of antennas tooffer its equivalent circuit. All these approaches begin bydetermining the impedance of these surfaces (called High126 A. FERCHICHI, A. GHARSALLAHFig. 1. An electrical model to the EBG cellule.Impedance Surfaces). From the expression of the impedance,we calculate electrical parameters model. Indeed, the high-impedance surfaces were introduced by D. Sievenpieper etal for the first time in order to remove surface waves patchantenna to increase its performance [13].In the literature, two models are proposed for the study ofSHI: the quasi-static and D. F. Sievenpieper introduced bythe dynamic model introduced by Simovski and all, [14]. Forboth cases, the approximation of the expression level of theimpedance changing.Zs =EH=Zs(TM) =jαωεavec α =ωc√ωα2σ(1− j)Zs(TE) =−jωµαD. F. Siervenpiper ExpressionZs =j√εrtan(k√εrh)1−ka(1 + εr)pi√εrlog( 2apig)tan(k√εrh)C. R. Simovski ExpressionBased on the error in the accuracy of the resonant frequency,the model D. Sievenpieper which is most effective with anerror rate of 10%. For this reason, we have adopted the modelof D. Sievenpieper to calculate the parameters of the electricalmodel. Thus, LR and CL can be calculated using equations:LR = µ0µrhCL =bε0(1 + εr)piA cosh(ag)With:h: thickness of substrate,b: width of metallic element,A: distance between the metallic elements,g: width gap.III. THE PROPOSED EBG ANTENNADue to the advantages of creating an EBG surfaces, we useit near to a simple antenna in order to see the modificationantenna parameter.A. GeometryIn our case, we have chosen to create an EBG surface nearto a rectangular patch. First we place the via hole in the centerof each metallic patch then we use a coaxial excitation to ourplanar antenna. This circuit is mounted in a planar structurewith a substrate and a ground plane. The whole structure isput into a box. The substrate we used is FR4 epoxy witha permittivity εr = 4.4 and a height h = 1.6mm. The twodesigns are shown in Fig. 2.Fig. 2. The geometry of the two designs of EBG structure.B. The Proposed Electrical Model for the EBG AntennaEBG structures (Electromagnetic Band Gap) have manyadvantages and are currently used in several applications.Among these applications, we use these structures for antennaswith high gain and directivity. In our work, we thought to usethese forms as antennas for RFID reader. The use of thesestructures is not clear due to the lack of analytical equationsfor controlling the parameters of the antenna according to thegeometry of the antenna. Indeed, the geometry of the antennais very complex for we are obliged to determine severalparameters such as the geometrical dimensions of the patch,the geometrical dimensions of the metal pad, the spacingbetween the metal and stone setting optimal characteristicsthe via hole: diameter and position.Thus, the electric model then becomes an indispensabletool that allows us to find a direct relationship betweenthe resonance frequency of an EBG structure and all thesegeometric parameters from the electric model. The latter isconstructed in the following steps:• Replace each elementary metallic cellule by an electricmodel (Fig. 1).• Modeling the coupling between the metal blocks bya coupling capacitance as explaining in our previousworks, [15].• Replace the patch antenna excited by a coaxial cable byits RLC electrical model (Fig. 3). The parameters modelcan be calculated using the equation developed in ourprevious works, [16], [17].Fig. 3. An electrical model to rectangular patch.A CIRCUIT MODEL TO A DIRECTIVE TRIANGULAR EBG ANTENNA 127• Modeling the coupling between the patch and the sur-rounding pavement by a coupling capacitance.To validate our model, we took an EBG structure consistingof four rows of metal blocks surrounding a patch antenna as anantenna Mushroom. The proposed electrical model is shownin Fig. 4.Fig. 4. The electrical model of proposed EBG structure.C. Result of SimualationFor this type of structures, the simulation takes a long timeespecially if you take a large number of metal blocks. Theincrease in metal blocks makes the simulation very slow HFSSand may take several hours! In our case, the simulation inHFSS rectangular patch with four rows of stones is hard metal38 minutes. The simulation model electric gave us results inless than a second.Simulation results are shown in Fig. 5.In order to compare the obtained result by using each tool:HFSS and electrical model, we dress Tab. I.TABLE ICOMPARISON BETWEEN ELECTRICAL MODEL RESULTS AND HFSSRESULTS OF PROPOSED ANTENNAAntenna HFSS Electrical ModelResonant frequency (GHz) 2.45 2.45BW (MHz) 100 50Simulation Time 38 minute 1.5 secondsAs can be seen in the table, the proposed model gives us thesame resonant frequency of HFSS in a very short time. Thus,we can use the proposed model in an analytic study whenmodifying one of geometrical antenna parameter. Once theneeded resonant frequency is obtained; we can also calculateFig. 5. Return loss of the proposed EBG structure.the physical parameter of the antenna from the lumped elementwhich seems very interesting. We note also, that the proposedmodel has a narrow band width comparing to real patch dueto differences between the real losses and those calculated bythe circuit model.IV. THE PROPOSED DIRECTIVE TRIANGULAR EBGANTENNAIn this last section, we tried to combine two techniquesin order to propose a directive EBG antenna by placing twogrilled surfaces near to EBG structure. First, we begin bychoosing the best EBG surface. Then, we design a simpleEBG triangular patch. Finally, we design the proposed designby introducing the two metallic grilles.A. EBG SurfaceIn our case, we have chosen to do a comparison betweenthe EBG parameter when we changing the via hole position.First we place the via hole in the center of the metallic patchthen we put it in the middle of one side of the square patch.This circuit is mounted in a planar structure with a substrateand a ground plane. The whole structure is put into a box. Thesubstrate we used is FR4 epoxy with a permittivity εr = 4.4and a height h = 1.6mm. The two designs are shown in Fig. 6.Fig. 6. The two EBG surface.According to the simulation results (Fig. 7), we note thatthe two Mushroom structures present two different bands Gap128 A. FERCHICHI, A. GHARSALLAHFig. 7. Simulation results of the two configuration of EBG structure.widths. Indeed, the position of the via hole has a major effecton the characteristics of these surfaces. In our case, it is clearthat the use of the structure with via the middle of one side ismore effective since it has some advantages, which include:• According to the reflection coefficient S11, the resonancefrequency is about 2.45 GHz which is a frequency RFID.• According to the transmission coefficient S21, the struc-ture has a band gap between 2.25 GHz and 2.8 GHz.As the frequency of work of the proposed antenna(2.45GHz) is in the band gap structure [2.25GHz, 2.8GHz],a direct influence on the radiation parameters of our antennais obtained.B. First EBG Triangular StructureTo take advantage of Mushroom structures, it was thoughtto simulate a triangular antenna in a Mushroom (Fig. 8).The simulation of the proposed EBG antenna, gave usthe reflection coefficient S11 shown in Fig. 5. We note thatour antenna has a resonant frequency equal to 2.45GHz anda bandwidth of about 90 MHz. Besides, the proposed antennahas a very high gain equal to 14.9dB (Fig. 9).Fig. 8. The triangular EBG antenna.Fig. 9. Simulation result of EBG triangular patch.C. The Proposed Grilled EBG Traiangular AntennaThe novel geometry is presented in Fig. 10. We used thesame substrate as above but we change only the rectangularby a triangular antenna.A CIRCUIT MODEL TO A DIRECTIVE TRIANGULAR EBG ANTENNA 129Fig. 10. The proposed grilled triangular EBG antenna.D. Result of SimulationThe simulation of the proposed EBG antenna, gave us thereflection coefficient S11 shown in Fig. 11. We note thatour antenna has a resonant frequency equal to 2.45GHz anda bandwidth of about 100 MHz. Besides, the proposed antennahas a very high directivity equal to 24.84dB.a)b)Fig. 11. Simulation result of grilled triangular EBG antenna. a) return lossb) directivity.As figured in Tab. II, we note that both the antennasimulated with HFSS and the electrical model has the sameresonant frequency and a comparable band width. But when,seeing the simulation time, we can say that the electrical modelis very fast which can be useful in antenna design step.TABLE IICOMPARISON BETWEEN ELECTRICAL MODEL RESULTS AND HFSSRESULTS OF DIRECTIVE TRIANGULAR EBG ANTENNAAntenna HFSS Electrical ModelResonant frequency (GHz) 2.45 2.45BW (MHz) 100 70Simulation Time 3h.24min 1.5secondV. CONCLUSIONA new directive EBG antenna was designed and evaluated.The proposed antennas have a resonant frequency equal to2.45 GHz and it presents a very high directivity which canameliorate the performance of RF systems. The circuit modelbased on simple lumped element was a very useful and fasttool to simplify the design, the simulation and the control ofthe entire parameter antenna.REFERENCES[1] F. Yang and Y. Rahmat-Samii, Electromagnetic Band Gap structure inAntenna Engineering. Cambridge University Press, 2009.[2] ——, “Microstrip antennas integrated with electromagnetic band-gap(EBG) structures: A low mutual coupling design for array applications,”IEEE Transactions on Antennas Propagation, vol. 51, no. 10, pp. 2936–2946, October 2003.[3] A. E. I. Lamminen, A. R. Vimpari, and J. Sa¨ily, “UC-EBG on LTCCfor 60-GHz frequency band antenna applications,” IEEE Transactions onAntennas Propagation, vol. 57, no. 10, pp. 2904–2912, October 2009.[4] R. Baggen, M. Martinez-Vazquez, J. Leiss, S. Holzwarth, L. S. Drioli,and P. deMaagt, “Low profile Galileo antenna using EBG technology,”IEEE Transactions on Antennas Propagation, vol. 56, no. 3, pp. 667–674, March 2008.[5] L. Li, X. J. Dang, B. Li, and C. H. 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A Circuit Model to a Directive Triangular EBG Antenna

Abstract—In This paper, we propose a directive triangular EBG antenna. This approach is derived from using an EBG surface near to a triangular patch with two grilles. The antenna frequency chosen is the 2.45GHz. The directive antenna is simulated by using HFSS and Electrical model. This proposed antenna presents a very high directivity. Keywords—EBG antenna, directive antenna, lumped element, mushroom I

Abdelhak Ferchichi

Ali Gharsallah

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A Circuit Model to a Directive Triangular EBG Antenna

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