In this paper, the bow-tie microstrip antennas have been designed with two different angles of 40Â° and 80Â°. An investigaton on the effect of the angle to the return loss and radiation patterns had been carried out. The impedance matching network with the niicrostrip transmission line feeding was used in this study. Simulation and measurement results for the return loss and radiation patterns were presented

Abdul Aziz, M. Z. A.

Goh, C. S.

Rahim, M. K. A.

English

Universiti Teknologi Malaysia Institutional Repository

BOW-TIE MICROSTRIP ANTENNADESIGNM.K.A. Rahim, M.Z.A. Abdul Aziz, C.S.GohWireless Communication Centre, Faculty of Electrical Engineering, Universiti TeknologiMalaysia813 10 UTM Skudai, Johor Malaysiaemail:mkamal@fke.utm-my, matjoingyahoo.com.csgoh@yahoo.comABSTRACTIn this paper, the bow-tie microstrip antennas have been designedwith two different angles of 400 and 80°. An investigaton on theeffect of the angle to the return loss and radiation patterns hadbeen carried out. The impedance matching network with theniicrostrip transmission line feeding was used in this study.Simulation and measurement results for the return loss andradiation patterns were presentedII. DESIGN CONSIDERATIONANTENNAOF BOW TIEFigure 1 shows the dimension of a bow-tie micirostripantenna, where a is the side length of the bow-tie strip, 0 isthe angle of equilateral triangular, L1, L2. W1, and W2 are thedimensions of the matching network. Resonant frequencycorresponding to the various modes described by [7]:1. INTRODUCTIONIn recent years, microstrip antennas have been widely used inboth theoretical research and engineering applications due totheir light weight and thin profile configurations, low cost offabrication, reliability, conformal structure and ease offabrication.The bow-tie microstrip antennas have been designed forwireless LAN application, where the operating frequency is at2.4 GHz. The bow-tie patch actually is the combination ofimaginary image of two triangular patches which arefabricated in a single substrate. Figure 1 shows the bow-tiestrip of a bow-tie microstrip antenna. Bow-tie microstripantennas have become attractive candidates in the present daycommunication scenario due to their compact naturecompared to rectangular patches. The ever increasing demandfor compact wireless communication equipment explicitlynecessitates research in compact antenna options and whichsparked interests of many researchers world wide in the fieldof bow-tie microstrip antennas.However in the literature, only very few attempts have beenmade towards the analysis of this type antenna. The bow-tiepatch microstrip antenna as a compact one, and suggested anempirical formula for the resonant frequency of this newgeodesy. The past research work on bow-tie antenna can beseen in [1-6]fr _ Ckmn2472c in2 ±mn+n2fr J3a-£r(1)(2)wherefr is the resonance frequencykmn is the resonating modesm and n are nombor ofmodesc is the velocity of light in free space.a is the side length of the bow tie stripThe above expression is valid when the triangular resonator issurrounded by a perfect magnetic wall. The effect of a nonperfect magnetic wall on the resonant frequency can beincluded in an empirical fashion for easy calculation.1-4244-0000-7/05/$20.00 02005 IEEE. 17W4W2Figure 1 Dimension ofBow Tie Microstrip AntennaResonant frequency for mn mode:fmn in2 +mn+n2Wavelength in free space:cA =-0fWavelength ofthe antenna:Ag= rCeffA number of suggestions have been made with regard to howto modify [81 to yield an accurate expression for a triangularmicrostrip patch antenna that is not enclosed by a perfectmagnetic wall. Most of the suggestions are about replacingthe side length a by an effective value aeff and leaving thesubstrate dielectric constant unchanged. The other set ofsuggestions proposes replacing both a and cr with theireffective values. An expression for aeffhas been arrived at bycurve fitting the experinmental and theoretical results for theresonant frequency for TMIO mode. It is given byI = digWhere d is the valueSmith chart4(10)of "wavelength towards load" in the(1 1)Resonant frequency dominant mode is:2c0-_2fj-W geAd e2A _2(3)W_-2B-1-ll1(2B-)W 1>4B-p)+0 39 0 11dL 2Er crfor -> 2dEffective value of side length:haeff=a+Er(5)Effective dielectric constant:Er + 6r)-1eff 2 + (6)4 1+aAccuracy of this empirical expression is claimed to be withinI % when compared with the value obtained from themoment method analysis. Knowing flo from above, theresonant frequency for higher order modes is calculated from(1), that isZ E I+ cr -1I 0.11Where A = ° r + £ (0.23+ )60 2 Er + 1 Er377,r2Z0gI1I. SIMULATION AND EXPERIMENTAL RESULT(A) Return Loss ResultThe input return loss is shown in figure 2 and 3 with differentvalue of angle (0). Figure 2 shows the simulation result forangle 0 = 40° with a return loss of-23.6dB at the operatingfrequency of2.4 GHz, while the measurement retum loss is -18(7)(8)(9)Side length:2c2frThwfor -< 2d(12)(4) (13)27.71dB at 2.48GHz.The BW from the measurement andsimulation result is nearly 3%.Figure 3 shows -19.91 dB return loss from simulation atoperating frequency of 2.42GHz, while the measurementreturn loss is -28.92dB at 2.48GHz. The angle is at 0 = 80° .In considering that all the simulation and measurement returnloss for both antenna having the return of lower than -20dB,therefore the incoming signal is strong enough to be receivedat the receiver.The shifting of the frequency is due to the substrate of FR4which has dielectric constant between 4.0 and 4.7. In thisdesign the dielectric constant is 4.7. The shifting of thefrequency is also from the fabrication process of the hardwareFigure 2 Simulation and measurement return loss ofthe antenna with 0 = 40°(b) H PlaneFigure 3 Simulation and measurement return loss ofthe antenna with 0= 80°(B) Radiation pattern characteristicFigure 4 and 5 show the radiation pattem for two differentangle for E and H Plane. The cross-polar isolation radiationpattern for 0 = 400 is nearly 20 dB for E Plane while for theH Plane has a very low cross polarization isolation. Thebeamwidth is 70 0 to 800. The result for 0 = 80° is slightlydifferent in term of the radiation pattem. It has a narrowbandwidth compared with aan angle 0 = 400. The cross polarisolation for both plane has a higher value than when 0 = 400 .The plotting in red colour is a co polarization while in bluecolour is a cross polarization.(a) E PlaneFigure 4400Radiation patterns of the antenna with 0 =(a) E Plane19V. CONCLUSIONThe BW from the measurement and simulation result is nearly3% with a return loss more than 20 dB. The angle ofthe bow-tie microstrip antennas does not affect its return loss. As longas the design of the matching network is correct, the desiredreturn loss can be obtained. The radiation pattern for highervalue of angle (0) give a radiation pattem more directionalwith a HPBW of400 to 500 for E plane and 200 to 300 for Hplane.REFERENCES(b) H PlaneFigure 5 Radiation patterns of the antenna with 0= 800IV. DISCUSSIONThe bow-tie patch antenna is a combination of imaginaryimage of two triangular patches which are fabricated in asingle substrate. Therefore, the design of bow-tie microstripantenna is based on the design of triangular microstripantenna. Those formula used in the design of triangularmicrostrip antenna to calculate the side length, effective valueof side length and effective value of dielectric constant, arealso applicable in the design of bow-tie microstrip antenna.For the design of bow-tie antenna, the side length iscalculated and fix at a certain operating frequency. While thelength is depends on the angle of the equilateral triangular,where the angle, 0 is not less than 00 and not bigger than1800. Therefore, the bow-tie microstrip antenna can be designat any degree of 0.There is an impedance matching network with the microstriptransmission line feeding which are fabricated simultaneouslywith the antenna structure. The impedance matching networkis the most important part in the design of a microstripantenna in order to minimize the return loss. The acceptablereturn loss for a microstrip antenna is - OdB or below. It isbetter if the microstrip antenna having the return loss of lowerthan -20dB.By comparing the simulation results and the measurementresults, we can notice that the return loss of the antennas withsame angle is different. It is may be caused by these factors,they are: inaccurate in preparing the layout, impurities of theequipment used for fabrication and the quality ofthe substrateand connector.The bow-tie microstrip antennas which have been fabricatedare with the angle of 40° and 80°.The simulation results ofthese designed antennas having the return loss of -23.6dB and-19.9dB respectively. While for the fabricated antennas withthe angle of 400 and 80°, the return losses are -27.7IdB and -28.91dB respectively.[1] Yu-De Lin and Syh-Nan Tsai, "Coplanar waveguide-feduniplanar bow-tie antenna,'" IEEE Trans. On Antennasand Propagation, vol. 45, Issue 2, pp. 305-306, Feb.1997.[21 Yu-De Lin and Syh-Nan Tsai, "Analysis and design ofbroadside-coupled striplines fed bow-tie antennas,"IEEE Trans. On Antennas and Propagation, Vol. 46,Issue 3, pp. 459-460. March 1998.[31 K. Iwami, T. Ono, E. Oesterschulze and M. Esashi,"Electrostatic actuator integrated optical near field-probe with bow-tie antenna for high transmissionefficiency," 12th International Conference on Actuatorsand Microsystem, Vol 1, pp. 548-551, 8-12 June 2003.[41 A. A. Lestari, A. G. Yarovoy and L.P Ligthart, "Adaptioncapabilities of a wire bow-tie antenna for groundpenetrating radar." IEEE Antennas and PropagationSociety International Symposium, Vol 2, pp 564-567, 8-13 July 2001.[51 K.L Shlager, G.S Smith, J.G Maloney, "Optimization ofbow-tie antennas for pulse radiation," IEEE Trans. OnAntennas and Propagation Vol 42, Issue 7, pp 975-982,July 1984.[6] Z. Guiping, A.A Kishk, A.B Yakovlev and A.W Glisson," A Broadbandprinted bow-tie antenna with a simplifiedfeed, " IEEE Ant. and Propagation Society InternationalSysmposium, Vol. 4, pp. 4024-4027, 20-25 June 2004.[7] X. Gang, "On the resonant frequencies ofmicrostrip antennas, " IEEE Trans. AntennasPropagat., vol.37, no. 2, pp. 245-247, 1989.[8] J.S. Dahele and K.F. Lee, "On the resonant frequenciesofthe triangular patch antenna, " IEEE Trans. AntennasPropagat., vol. AP-35, no. I, pp.100-101, 1987.[9] R. Garg and S.A. Long, "An improvedformulafor theresonantfreq uency ofthe triangular microstripantenna, IEEE Trans. Antennas Propagat., vol.36, pp. 570, 1988.[10] R. Singh, A De, and R S. Yadava, " Comments on animprovedformulafor the resonantfrequency of thetriangular microstrip patch antenna, " IEEE Trans.Antennas Propagat., vol. 39, pp. 1443-1445, 1991.[111 K. Guney, "Resonantfrequency ofa triangularmicrostrip antenna, Microwave and OpticalTechnology Letters, vol. 6, no. 9, pp. 555-557, 1993.[121 I.J. Bahl and P. Bhartia, Microstrip Antennas.Dedham, MA: Artech, 1980.20

Bow-Tie Microstrip Antenna Design

http://eprints.utm.my/2206/1/RahimAzizGoh2005__BowTieMicrostripAntennaDesign.pdf

Bow-Tie Microstrip Antenna Design

Abstract

Similar works

Full text

Available Versions

Universiti Teknologi Malaysia Institutional Repository