DESIGN OF PRINTED DIPOLE ANTENNA AND ITS APPLICATIONS IN UMTS MOBILE COMMUNICATION NETWORKS Buak TOMBALOĞLU, Doğan DİBEKÇİ Kocaeli Univesity, Electonic and Communication Eng. Dept. Kocaeli. e-mail: buak.tombaloglu@tuktelekom.com.t, ddibekci@kou.edu.t Key wods: UMTS, Pinted Dipole Antenna ABSTRACT This pape pesents the design of a pinted dipole antenna which woks at UMTS (Univesal Mobile Telecommunications System) band. The design of the pinted dipole antenna which is one of the types of antennas used in these netwoks is examined. A pinted dipole which can be used in UMTS communication applications and woks at 2,1 GHz ezonance fequency was designed. It is simulated by the Ansoft HFSS, the 3D finite-element-method (FEM) electomagnetic EM Simulato. A pactical application of this antenna has been ealized and the esonance fequency is measued. Both pactical measuements and the simulation esults ae consistent with the design of the antenna. 1. INTRODUCTION UMTS netwok achitectue is GSM based and the diffeences between these netwoks ae adio fequency band, adio units, adio intefaces and adio access. 2. ANTENNA TECHNIQUES USED IN MOBILE COMMUNICATION AND PRINTED DIPOLE ANTENNA DESIGN 2.1. Pinted Dipole Antenna with Integated Balun As shown in Figue 2.1., the pinted dipole antenna has a co-axial feed line which behaves like unbalanced-tobalanced and a micostip balun between two pinted dipole stips. Both the length of the dipole stip and micostip balun is appoximately quate of the wavelength (/). The base suface of the micostip line and dipole antenna stips ae on the same plane. The hole lets the feed point 2 be at the same phase with the feed point 1. Because of the 180º phase diffeence between the uppe stip and the bottom suface, thee is 180º phase diffeence between the feding point 2 in the pinted dipole stip and the feding point 1 [3]. One of the antenna types that used in both in GSM and UMTS netwoks is pinted dipole antenna. The design of a pinted dipole antenna which woks at UMTS band is examined. Fo the dipole design, HFSS (High Fequency Stuctue Simulato) by Ansoft which uses Finite Element Method (FEM) is used. By using the simulation softwae, the antenna etun loss change by fequency is ealized. Constucting of the antenna a pinted cicuit boad which has = 2,38 is used. Retun Loss measuement is elalized by using Agilent 871ES RF Netwok Analyze. Figue 2.1. : Pinted Dipole Antenna with Micostip Balun [3] 2.1.1. Folded balun A folded balun (Figue 2.2.) povides a diect connection between the dipole and the coaxial line. Oute conducte is connected to a pole which is fed by a imitation cental conducte. Oute conducto goes with feeding dipole side by side / distance and is connected to gound. The othe pole is diectly connected to the shield of the feede
coaxial. The oute conducte of the coaxial and the exta line ae two lines in the gounded thee line. Figue 2.5. : Co-axial Equivalent of The Pinted Dipole Antenna Figue 2.2. : Folded Balun [6] Figue 2.6. : Cicuit Equivalent of The Pinted Dipole Antenna Figue 2.3. : Cicuit Equivalent of Balun[] If h =, esonance fequency, Z BALUN is infinitive. 2π Z BALUN = JZbtg = [] (2.1.) If L a = esonance fequency, Z BALUN is infinitive. 2π Z BALUN = JZatg = (2.2.) 2.2. Calculations of the Dimensions The length of the dipole ams and the balun is quate of the wavelength. To calculate the wavelength, the following fomula is used. c = [6] (2.3.) f eff : Wavelength, c: Speed of Light = 3.10 8 m/s, eff : Effective Dielectic Constant Figue 2.. : Pinted Dipole Antenna
3. ANSOFT HFSS HFSS, is a 3D EM simulation softwae which is poduced fo RF and wieless design by Ansoft Company. At the fist time it was intoduced as a fist commecial softwae simulating complex 3D geometics in 1990. The softwae allows the design enginees to use the finite element method[1]. HFSS is a softwae package which calculates s- paametes and full wave fields fo andom shaped 3D passive stuctues. The stuctues ae simulated using the Finite Element Method (FEM). Figue 2.7. : The geomety of The Pinted Dipole Antenna [3] The dielectic constant of the assembled pinted cicuit boad is measued. Afte measuing the capacity of the boad, dielectic constant is calculated by the following equation. A C = (2..) d C= 255 pf, boad aea A=133,3.10 - m 2, dielectic thickness d=1,1.10-3 m ae measued. 0 = (2.5.) 12 = 8,85. F/m and = 2, 38 0 10 eff F/m is found. : Effective Dielectic Constant of the micostip tansmission lines, + 1 1 eff = + [6] (2.6.) 2 2 1+ 10H / W Analyzing antennas, waveguide components, RF filtes and many othe stuctues is as simple as dawing the stuctue, specifying mateial chaacteistics, and identifying pots and special suface chaacteistics. HFSS automatically geneates field solutions, pot chaacteistics, and s-paametes. It is quickly able to calculate antenna metics such as gain, diectivity, fafield patten cuts, fa-field 3D plots, and 3dB beamwidth[1]. 3.1.Finite Element Method (FEM) In ode to geneate an electomagnetic field solution, Ansoft HFSS employs the finite element method. In geneal, the finite element method divides the full poblem space into thousands of smalle egions and epesents the field in each sub-egion (element) with a local function. In Ansoft HFSS, the geometic model is automatically divided into a lage numbe of tetaheda, whee a single tetahedon is basically a fou-sided pyamid. This collection of tetaheda is efeed to as the finite element mesh[7]. H: Dielectic laye thickness, W: Stip thickness Fo = 2,38 F/m, H = 1,1.10-3 m, W = 6.10-3 m, eff = 2,1 is found. The esonance fequency is 2,1 GHz. If we get eff = 2,1, f = 2,1 GHz, = Ld = 2,6 mm is found. The pats of the pinted dipole = L d = Lb + Lh = 2 mm ae designed. Figue 3.1. : Mesh of the the model analized.
. SIMULATION AND APPLICATION OF THE 2.1 GHz PRINTED DIPOLE ANTENNA WITH MICROSTRIP BALUN The pinted dipole antenna with a micostip balun is assembled on a pinted cicuit boad (PCB). The antenna is simulated by the 3D softwae Ansoft HFSS using Finite Element Method..1. Pinted Dipole Antenna Model Simulated Design simulation and constuction of the pinted dipole antenna 2,1 GHz esonance is assembeled on coppe double sided pinted cicuit boad (FR-). Micostip balun and dipole am dimensions ae designed as, W g = 15 mm, L g = 10 mm, L b = 21 mm, L h = 3 mm, L d =2 mm, g 2 = 3 mm, W d = 6 mm, L f = 3 mm, g 1 = 1 mm, W h = 3 mm, W f = 3 mm, h = 1.2 mm. (Figue.1.) Figue.3. : Measuement Mechanism Measuements ae ealized with Agilent 871ES RF Netwok Analyze (Figue.3.) Figue.1. : The geomety of the Pinted Dipole Antenna[3] The photos of the designed antenna ae at the below. Figue.. : HFSS Pinted Dipole Antenna Model Fo.2. Simulation and Measuement Results eff = 2,1 and f = 2,1 GHz, is equals 2,6 mm. Dimensions of the balun and the dipole ams ae calculated accoding to = 2 mm. The following etun loss chaacteistics ae ealized afte the measuements and simulations. Figue.2. : 2.1 GHz Micostip Pinted Dipole Antenna a) Uppeside b) Undeside
Figue.5. : The Retun Loss (db) Chaacteistics ealised afte the measuements and the simulations As shown in the the Retun Loss (db) Gaph (Figue.5), the esonance fequency measued 2,1 GHz in HFSS softwae and the osonance fequency of the pactical application is 2,160 GHz. 5. RESULTS AND SUGGESTIONS In this study, a pinted dipole which woks at UMTS band is designed. Fo dipole design, HFSS (High Fequency Stuctue Simulato) softwae devoloped by Ansoft Company is used. The Retun Loss and the adiation pattens of the antenna is ealised using the simulation softwae. A pinted cicuit boad which has = 2,38 is used. Retun Loss is is measued with Agilent 871ES RF Netwok Analyze. The dielectic coefficient of the pinted cicuit boad effects the dipole dimensions. The faulty measuement of the dielectic coefficient causes diffeent esonant fequecies fom 2,1 GHz. In the design model the dielectic coefficient of the pinted cicuit boad is measued as = 2,38. The dimensions ae calculated using this value. Retun Loss change by fequency is ealised fom simulation and measuement esults. In HFSS, the esonance fequency is measued 2,1 GHz and it is measued 2,160 GHz in pactical measuement esults. REFERENCES 1. AZMAN, V., 2002. Confomal Antenna Aays fo 3G Cellula Base Stations, The School of Infomation Technology and Electical Engineeing Univesity of Queensland, Austalia. 2. CHUANG, H., KUO, L., LIN, C., CHEN, W., 2002. A 2. GHz Polaization Divesity Plana Pinted Dipole Antenna fo WLAN and Wieless Communication Applications, National Cheng Kung Univesity, Tainan, Taiwan, www.swissatv.ch 3. FUJIMOTO K., JAMES J. R., 199. Mobile Antenna Systems Handbook, Atech House Inc., Nowood.. HETTAK K., DELISLE G.Y., STUBBS M.G., 2001. "A Novel Vaiant of Dual Polaized CPW Fed Patch Antenna fo Boadband Wieless Communications," IEEE Antennas and Popagation Society Intenational Symposium Digest, Vol.1, pp. 286-289. 5. ZHU L., WU K., 1999. "Model - based Chaacteization of CPS-fed Pinted Dipole fo Innovative Design of Uniplana Integated Antenna," IEEE Micowave and Guided Wave Lettes, Vol. 9, No. 9, pp. 32-3. 6. MICHISHITAI N., ARAI H., 2001. "A Polaizationdivesity Antenna by Pinted Dipole and Patch With a Hole," IEEE Antennas and Popagation Society Intenational Symposium Digest, pp. 368-371. 7. CHUANG, H., KUO, L., 2003. 3 -D FDTD Design Analysis of a 2. - GHz Polaization - Divesity Pinted Dipole Antenna With Integated Balun and Polaization Switching Cicuit fo WLAN and Wieless Communication Applications, IEEE Tansactions on Micowave Theoy and Techniques, VOL. 51, NO. 2. 8. EDWARD B., REES D., 1987. A boadband pinted dipole with integated balun, Micowave J., pp. 339 3. 9. GRUPO DE RADIACION, 2003. Cuso 2003-200 Tanspaencias- Antennas Lineales, Univesidad Politécnica, Madid, www.g.ss.upm.es 10. NIKOLOVA, N. K., 2003. Lectue 10: Othe Pactical Dipole / Monopole Geometies. Matching Techiniques fo Dipole / Monopole Feeds, McMaste Univesity, www.ece.mcmaste.ca 11. MILLIGAN, A. T., 1985. Moden Antenna Design, McGRAW-HILL Book Company 12. ANSOFT, 2003. HFSS V 9.0 Help Technical Notes 13. www.ansoft.com Both pactical measuements and the simulation esults ae consistent with the design of the antenna.