A compact UWB slot antenna optimized by genetic algorithm
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optimized parameters of the proposed antenna are as follows:W 1¼21.10mm,W 2¼17.95mm,W 3¼3.15mm,W 4¼5.95mm,L 1¼27.55mm,L 2¼13.15mm,L 3¼2.50mm,L 4¼11.90mm,L 5¼1.91mm,L 6¼9.84mm,L 7¼4.45mm,L 8¼4.70mm,wire length ¼798mm,wire width ¼0.2mm,and space between wires ¼0.15mm.Figure 2shows the 3D view and feeding structure of the pro-posed antenna with the ferrite sheet.The monopole antenna is located at the rear cover against the main printed circuits board (PCB)of a FR4substrate with 50Â100mm 2considered to be the size of circuit board of a mobile handset.This design,a radiating element with an area of 21.10Â27.55mm 2,is printed on a dielectric material flexible PCB (FPCB)substrate of 0.035mm and 3.5relative permittivity.Also,a magneto-dielectric ma-terial ferrite sheet substrate of 0.2mm,9.00relative permittivity (dielectric loss tangent:under 0.01),and 9.00relative permeabil-ity (magnetic loss tangent:under 0.05)is attached on the antenna pattern for FM bandwidth (EMW ferrite sheet).The proposed antenna is fed by a 50-X coaxial line which connects the inner conductor directly to the feeding part in the substrate.This antenna is designed to cover the frequency range of 86–108MHz,that is,the bandwidth of 40MHz related to the reso-nant frequencies at 92and 118MHz with an arrow-shaped patch.The proposed monopole antenna design is created using the Microwave Studio commercial software from Computer Simula-tion Technology.The proposed FM radio ferrite sheet antenna using an arrow-shaped patch to enhance gain performance for mo-bile handsets is constructed and measured for the FM bandwidth (86–108MHz),then RL is measured using an Agilent N5230A vector network analyzer.Its far-field patterns and gain are meas-ured inside a possible compact range at EMW Co.in Korea.Both the simulated and measured RLs of the proposed antenna with and without an arrow patch are shown in Figure 3.The measurement range is 83.20–123.72MHz,which reached approximately 40.52MHz,thus covering the FM systems (VSWR 6:1).The simulated result with an arrow-shaped patch has a wider band than the simulated result without an arrow-shaped patch.The range is 83.20–122.03MHz,which reached 38.73MHz (VSWR 6:1).Figure 4presents the measured RPs of the proposed antenna.The RPs are measured from 86to 108MHz.Good RPs are obtained at 86,97,and 108MHz (FM band).Figure 5shows the simulated and measured antenna gain for the operating fre-quencies with an arrow-shaped patch where the gain of À15.6–13.5dBi is obtained.The simulated result with an arrow-shaped patch has a higher passive gain than the simulated result without an arrow-shaped patch as 2–4dB.3.CONCLUSIONSIn this article,an internal FM radio ferrite sheet flexible antenna using an arrow-shaped patch to enhance passive gain performance for mobile handsets was designed,fabricated,and tested.The im-pedance bandwidths were 40.52MHz (83.20–123.72MHz),cov-ering the required FM radio bandwidth (86–108MHz).The gain obtained from À15.6to 13.5dBi matched the FM specifications.The radiation characteristics of the proposed antenna were also observed.The results demonstrate that the proposed internal FM radio ferrite sheet flexible antenna using an arrow-shaped patch enhanced passive gain performance for mobile handsets.REFERENCES1.P.Lindberg and A.Kaikkonen,Internal active antenna for FM ra-dio reception in mobile handsets,The Second European Confer-ence on Antennas and Propagation,(EuCAP)2007,pp.1–10.2.P.Lindberg,S.Irmscher,and A.Kaikkonen,Electrically small receive only resonant antenna with wideband performance for FM radio reception in mobile phones,International Workshop on Antenna Technology (iWAT),2010,pp.1–4.3.J.K.Park,Y.H.Choi,J.M.Kim,S.H.Kim,and J.S.Yoo,FM radio chip antenna using magneto-dielectric,Asia-Pacific Microwave Conference (APMC),Bangkok,Thailand,2007,pp.1–3.4.D.Aguilar,J.Anguera,C.Puente,and M.Ribo,Small handset antenna for FM reception,Microw Opt Technol Lett 50(2008),2677–2683.5.R.Devore and P.Bohley,The electrically small magnetically loaded multi-turn loop antenna,IEEE Trans Antennas Propag 25(1977),496–505.6.J.R.James and A.Henderson,Electrically short monopole antennas with dielectric or ferrite coatings,Proc Inst Electric Eng125(1978),793–803.7.M.I.Kitra,C.J.Panagamuwa,P.McEvoy,J.C.Vardaxoglou,and J.R.James,Low SAR ferrite handset antenna design,IEEE Trans Antenna Propag 55(2007),1155–1164.8.C.A.Balanis,Antenna theory,2nd ed.,Wiley,New York,NY,1997.VC 2011Wiley Periodicals,Inc.A COMPACT UWB SLOT ANTENNA OPTIMIZED BY GENETIC ALGORITHML.Xie,Y.-C.Jiao,Y.-Q.Wei,G.Zhao,and F .-S.Zhang National Laboratory of Antennas and Microwave Technology,Xidian University,Xi’an,Shaanxi 710071,China;Corresponding author:xielei0609@ Received 14December 2010ABSTRACT:A compact ultra-wideband (UWB)slot antenna based on a mesh-grid structure is designed.A genetic algorithm is used to optimize the mesh-grid structure as well as other parameters of the proposed antenna for good impedance matching in the UWB band.The optimized UWB antenna has a compact size of 24mm Â30mm and is fabricated and measured.According to the measured results,the proposed antenna yields a wide bandwidth,defined by VSWR <2,ranging from 3.1to 12.2GHz and a nearly omnidirectional radiation pattern in the H-plane.The antenna gains within the matching band are measured and a gainvariation from 3.1to 5.9dBi is obtained.VC 2011Wiley Periodicals,Inc.Microwave Opt Technol Lett 53:2135–2139,2011;View this article online at .DOI 10.1002/mop.26179Key words:ultra-wideband antenna;genetic algorithm;microstripantennaFigure 5Simulated and measured gain for the proposed antenna with and without an arrow patch1.INTRODUCTIONBecause of the rapid development of ultra-wideband (UWB)communication systems in recent years,much research has been conducted on UWB antennas,among which printed wide slot antennas have been regarded as popular candidates [1–5].All these antenna designs have attempted to change the coupling between the feed line and the slot by designing special shapes for the feed line or for both the feed line and the slot.In Ref.6,a loading structure was proposed to enhance the impedance bandwidth of UWB slot antennas.Both experimental and simu-lated results have shown the effectiveness of this method.Genetic algorithm (GA)optimized mesh-grid structure has been widely used in electromagnetic designs,such as microstrip patch antenna [7],planar monopole antenna [8],and frequency selective surface (FSS)[9].Compared with conventional struc-tures,this structure provides more degrees of freedom for opti-mizing the antenna.In this article,an UWB slot antenna with a slot of mesh-grid structure and a T-shaped feed line is introduced.The grids as well as the dimensions of the feed line are coded into a single binary chromosome and are optimized by a genetic algorithm.By optimizing the mesh-grid structure,both an appropriate slot shape and a loading structure are obtained,which have signifi-cantly enlarged the antenna’s impedance bandwidth.The opti-mized antenna is fabricated and measured.The measured results show good agreement with the simulated ones.Details of the antenna design and both the simulated and the measured results are presented and discussed.2.ANTENNA DESIGNThe antenna is printed on a 24mm Â30mm substrate with the thickness of 1mm and the dielectric constant of 2.65.As previ-ously mentioned,the center part of the ground plane consists ofa 10by 12grid of metallic subpatches.The overall dimensions of the grid structure are W s ¼20.2mm,L s ¼24.2mm,and P s ¼3.9mm.Each metallic subpatch of the grid structure can be switched ‘‘on’’or ‘‘off’’by the genetic algorithm.Figure 1shows all subpatches switched ‘‘on.’’Each subpatch is a 2.2mm  2.2mm square.They are overlapping by 0.2mm to ensure electrical contact in such constellations where two sub-patches are touching only at the corner.This is used to avoid impractical one-point subpatch contacts [9].The geometryofFigure 1Geometry of the proposedantennaFigure 2Geometry of overlappingsubpatchesFigure 3Geometry of the optimizedantennaFigure 4Photograph of the optimized antenna.[Color figure can be viewed in the online issue,which is available at]Figure 5Simulated and measured VSWR of the optimized antenna.[Color figure can be viewed in the online issue,which is available at ]the overlapping subpatches is shown in Figure 2.In the optimi-zation process,there are no constraints placed upon how sub-patches can be set,except that symmetry must be maintained along the antenna centerline.This is due to the fact that for UWB applications symmetrical and omnidirectional radiation pattern is required and thus symmetrical structure is usually preferred.The above-mentioned subpatches setting principle implies that various slot shapes may be created,and that frag-ments separate from the main ground plane may be created as a loading structure.Besides the grid of subpatches,the dimensions of the feed line which depend on the values of P r ,W r ,L r ,and W f should also be optimized.Each of these parameters is encoded with a binary code of length 7.Consequently,the structure of the antenna is represented by an 88-bitlongFigure 6Measured radiation patterns:(a) 3.1,(b)6,and (c)9GHz.[Color figure can be viewed in the online issue,which is available at ]binary code.Half of the grid structure is represented by the anterior60bits and the other half is symmetrical to it along the antenna centerline.The remaining28bits are divided into four parts and each part represents the value of P r,W r,L r,and W f,respectively.A simple GA optimizer is developed to optimize the band-width performance of the proposed antenna[10].The GA can be broken down into a series of procedures as follows:1.Creating an initial populationAs previously mentioned,the configuration of the antenna is represented by a chromosome consisting of88genes.A diverse population of30solutions is generated by ran-domly setting each gene to0or1.2.Evaluating the solutions’fitnessThefitness of the solutions is evaluated by using IE3D software which is based on method of moment[11].The fitness function for the antenna design is given by:f rmfitness¼min1NX10:6GHz3:1GHzVSWR1ðfÞ8>>>>:9>>>>;(1)VSWR1ðfÞ¼VSWR VSWR!1:81:8VSWR<1:8&(2)In formula(1),N is the number of the sample points within the band of 3.1–10.6GHz.Here we sample25 equidistant frequency points within the UWB band.3.Choosing the mating pairsThere exists a variety of techniques to choose which solutions should mate together to create a new genera-tion.Here,the binary tournament selection,which is regarded as the most successful one is used.This tech-nique picks two solutions out of the population at ran-dom and adds the solution with the betterfitness to the mating pool.4.Mating the solutions togetherIn our GA,a crossover probability of80%is used.To avoid gene pool stagnation,a multipoint crossover tech-nique is implemented.Each chromosome is randomly split up intofive segments.The offspring solutions are then generated using alternate segments of their parents.In a final effort to maintain variation within the gene pool, each gene in every chromosome is given a1%chance of mutation,causing it to switch from a0to a1or vice versa.3.RESULTS AND DISCUSSIONIn total,the GA ran for55generations before converging on an answer.The optimum values of P r,W r,L r,and W f are8.3,2.6, 6.6,and1.2mm,respectively.The geometry and photograph of the optimized antenna are shown in Figures3and4,respec-tively.And as we expected,a loading structure is obtained.The optimized antenna has been simulated using Zealand’s IE3D package and measured on a network analyzer.Figure5shows the simulated and measured voltage standing wave ratio (VSWR)of the optimized antenna,where a good agreement between the simulated and measured results is observed.From Figure5,we can see that the antenna has a bandwidth ranging from3.1to12.2GHz for VSWR<2,which is very attractive for UWB application.The normalized radiation patterns of the proposed antenna measured at3.1,6.0,and9.0GHz are shown in Figure6.It can be seen that the antenna exhibits a nearly omnidirectional radia-tion pattern in the H-plane(x–y plane)and a dipole-like radia-tion pattern in the E-plane(y–z plane).Finally,the antenna gains against frequencies through the matching band were measured. As shown in Figure7,the gains are about3.1–5.9dBi in the measured frequency band with the peak value of5.9dBi at8 GHz.4.CONCLUSIONSThe optimization of a compact UWB slot antenna has been implemented by Genetic Algorithm.By introducing a mesh-grid structure on the ground plane,the slot shape as well as the load-ing structure has been optimized simultaneously.The optimized antenna has a compact size of24mmÂ30mm and is fabri-cated and measured.Measured results have shown that the antenna has a bandwidth ranging from 3.1to12.2GHz and approximately omnidirectional radiation patterns.Accordingly, the proposed antenna is expected to be a good candidate in vari-ous UWB systems.REFERENCES1.J.N.Lee,J.K.Park,and S.S.Choi,Design of a compact frequency-notched UWB slot antenna,Microwave Opt Technol Lett48 (2006),105–107.2.J.-S.Sun,Y.-C.Lee,and S.-C.Lin,New design of a CPW-fedultrawideband slot antenna,Microwave Opt Technol Lett49 (2007),561–564.3.H.-D.Chen,J.-N.Li,and Y.-F.Huang,Band-notched ultra-wide-band square slot antenna,Microwave Opt Technol Lett48(2006), 2427–2429.4.C.-W.Chiu and C.-S.Li,A CPW-fed band-notched slot antennafor UWB applications,Microwave Opt Technol Lett51(2009), 1587–1592.5.M.Naser-Moghadasi,M.Koohestani,M.Golpour,and B.S.Vir-dee,Ultra-wideband square slot antenna with a novel diamond open-ended microstrip feed,Microwave Opt Technol Lett51 (2009),1075–1080.6.J.-Yi Sze and Jen-Yi Shiu,Design of band-notched ultrawidebandsquare aperture antenna with a hat-shaped back-patch,IEEE Trans Antennas Propag56(2008),3311–3314.7.C.H.and H.Ling,Design of broadband and dual-band microstripantennas on a high-dielectric substrate using a genetic algorithm, IEE Proc Microwave Antennas Propag150(2003),137–142.8.A.J.Kerkhoff,R.L.Rogers,and H.Ling,Design and analysis ofplanar monopole antennas using a genetic algorithm approach, IEEE Trans Antennas Propag52(2004),2709–2718.Figure7Measured antenna gain against frequency9.M.Ohira,H.Deguchi,M.Tsuji,and H.Shigesawa,Multiband sin-gle-layer frequency selective surface designed by combination of genetic algorithm and geometry-refinement technique,IEEE Trans Antennas Propag52(2004),2925–2931.10.J.M.Johnson and V.Rahmat-Samii,Genetic algorithms in engi-neering electromagnetics,IEEE Trans Antennas Propag39(1997), 7–21.11.X.F.Liu,Y.B.Chen,Y.C.Jiao,and F.S.Zhang,Modified particleswarm optimization for patch antenna design based on IE3D, J Electromagn Waves Appl21(2007),1819–1828.V C2011Wiley Periodicals,Inc.IMPROVED MEASUREMENT OF COMPLEX PERMITTIVITY USING ARTIFICIAL NEURAL NETWORKSWITH SCALED INPUTSAzhar Hasan and Andrew F.PetersonSchool of Electrical and Computer Engineering,Georgia Institute of Technology,Atlanta,GA30332-0250;Corresponding author: peterson@Received19November2010ABSTRACT:A procedure is described to enhance the accuracy of microwave measurements of the complex permittivity of a dissipative medium.Monopole probe measurements are used in conjunction with two real-valued neural networks,which are integrated together to reconstruct the complex permittivity from the measured reflectioncoefficients.The approach is tested over the frequency range from2.5to 5GHz,for the real part of the permittivity in the range3–10and the imaginary part in the range0–0.5.The performance of the network is also demonstrated for a reduced frequency range from3.5to5GHz. Less than4%error was observed in the presence of white Gaussian noise with an SNR of10dB.V C2011Wiley Periodicals,Inc.Microwave Opt Technol Lett53:2139–2142,2011;View this article online at .DOI10.1002/mop.26221Key words:neural network;complex permittivity;measurement; monopole;reflection coefficient1.INTRODUCTIONThe dielectric characterization of materials in the microwave frequency range uses a variety of resonant and nonresonant methods[1].A particularly simple technique uses a monopole probe immersed in the material under investigation;the input impedance of the probe provides sufficient information to extract the complex permittivity(e r).In one approach,the nor-malized impedance of the probe is expressed as a rational func-tion of order three and the coefficients of the function are deter-mined based on the profile of a standard medium[2].A more elaborate model for the impedance of a monopole antenna in a half space[3]can be used in conjunction with various in-situ procedures for solving the associated nonlinear inverse problem. In one approach,the dielectric values are calculated by compar-ing the measured and calculated values of the input impedance using an iterative two-dimensional complex zerofinding routine [4];in another,a least squarefit is used to match the measured and calculated input impedance[5];and in a third,an analysis of resonant peaks determined from the analytical model is used with Prony’s method[6].An alternate approach uses neural networks with a back-propagation algorithm to reconstruct the permittivity profile of lossless stratified medium from complex reflection coefficients [7].For a dissipative medium,the complex-valued nature of the permittivity makes the problem incompatible with conventional neural networks,which are designed to process real-valued data. One possible approach is to use a complex valued back propaga-tion neural network,which might result in better accuracy,but that is considered much more complicated to implement[8]. Another possible approach is to split the network into two net-works,one dealing with the real part and the other dealing with the imaginary part(with both using real valued input data).One such approach,for complex permittivity measurement,used the finite difference time domain technique to generate training data [9].However,the use of two networks leads to a loss of correla-tion between the real and imaginary parts of the complex input data[10].As there is usually considerable correlation between the real and imaginary parts of the complex data[11],such a loss reduces the accuracy of the results.This article proposes the use of two back propagation net-works,integrated together to reconstruct the complex permittiv-ity of dissipative media.Instead of separating the real and imagi-nary parts of the input data,the phase and magnitude of the complex reflection coefficients are used as inputs to each of the two back propagation networks,one of which solves for the real part of the complex permittivity,whereas the other solves for the imaginary part.Scaling is incorporated to improve the perform-ance in the presence of noise.To demonstrate the procedure,the analytical model of[3]will be used to train and test the neural networks.The analytical model is briefly discussed in Section2, and the neural network setup is described in Section3.The simu-lation results and analysis are presented in Section4.2.THE MONOPOLE ANTENNA MODELThe monopole antenna is widely used as a sensor probe for the in-situ characterization of soil moisture content[6],snow and soil wetness[5],and the measurement of electrical properties of materials[2].For a monopole probe immersed in a nonmagnetic dielectric medium,the input impedance(and reflection coeffi-cient)measured with a vector network analyzer(VNA)depends on the permittivity of the medium.The input impedance of the probe is related to the reflection coefficient through Eq.(1).C¼Z inÀZ oZ inþZ o(1)In Eq.(1),C is the complex reflection coefficient,Z in is the input impedance of the monopole probe,and Z o is the character-istic impedance of the coaxial cable connected to the probe, which in this case is50X.The input impedance Z in is computed using an expression developed by Wu[3],given byZÃin¼xl oj4kðSþCUÞ(2) wherekÀbþj a¼x½lð 0Àj 00Þ 1=2(3)The functions S,C,and U,along with the approximations in-herent in these expressions,are described in detail in Appendix A of[4].These functions along with k depend on the measure-ment frequency,the geometrical dimensions of the monopole。
