Planar Dipole Antenna Design At 1800MHz Band Using Different Feeding Methods For GSM Application

Planar Dipole Antenna Design At 1800MHz Band Using Different Feeding Methods For GSM Application Waleed Ahm ed AL Garidi, Norsuzlin Bt Mohad Saha r, Rozita Teym ourzadeh, CEng . Member IEEE/IET Faculty of Engineering, T echnology & B uilt Environment UCSI University, 560 00, Malaysia Email: rozita@ucsi.ed u.my Abstract - This research work focuses on the de sign and simulation of planar di pole a ntenna for 1800MHZ B and for Global System Mobile GS M application using Co mputer Software Technology CST studio s oftware. The antenna is structured on fire r esistance FR4 substrate w ith relative constant of 4.3 S/m. Two types of feeding configuration a re designed to feed the antenna in ord er to m atch 50 Ω transmission lines w hich are via-hole integrated balun an d quarter wavelength open stub. The via-hole is capable to provide maximum return loss of -25dB, band width of 18.4% and the voltage standing wave ratio ( VSWR) of 1.116 V at optimum dimension of length 59 mm and w idth 4mm; the bandw idth is improved 25% t o 30% by ex tending the w idth of the antenna 8 mm to 1 0 mm followed by dete rioration of return loss value to - 15dB. While t he open stub at length of 67 mm , w idth of 6 mm and height 1.6 mm w ill provide ma x ret urn lo ss of -47.8 8dB and bandwidth of 1 7% with V SWR 1.008 << 2. Way that t he antenna substrate has influ enced the perfor mance of t he antenna . The low er relative constant wil l result the higher return lows, narrower bandwidth and better radiation pattern in trade-off the resonant length Via -hole and then the quarter wave open stub are most convenient for practical imp lementation . Keywords -- Antenna, GSM, Plann er, Dipole , VSWR, MMIC , Microstrip I. I NTRODUCTION Antenna is playing significant role in the wireless communication systems. Radio frequency and Mi cro wave has direct effect o n an tenna for trance-receiving the signals a nd antenna will transmit it through the electro -ma gnetite wave in free space [1 ]. I n order to d esign a ntenna i n the bandwidth of 900MHz – 1800 MHz in the industr y of cellular network such as GSM net work, the IEEE Standar d [1 ] (Std 1 45-1983) is approached accordingly. The trends o f the mob ile phone tec hnology has been dramatically decreased the weight and size of the communication equip ment. Microstrip d ipole antennas consist of a thin sheet of lo w loss insulating called the dielectric substrate and i t is c ompletely co vered with a met al on one side called the ground plane. From the ot her side is par tly metalized where the circui t of antenna is p rinted [2 ]. In particular, planar dip ole- ty pe exhibits many attractive featu res, such as a s imple structure, inexpensive easy integratio n with monolithic microwave integrated circuits ( MMIC), low-profile, comfortable to pl anar and non-planar s urfaces. T herefore, it works best on air and portable application. Micro -strip dipole moment is attractive becau se they basically o wn large feature li ke simple analysis and manufacturing and its attractive radiation patter n particularly low bet ween-polarized rays. II . A NTENNA G EOMETRY DESIGN The desired freq uency that the dipole antenna is designed to o perate on is 18 00MHz GSM band. T he s ubstrate material has been used is FR4 with dielectric constant of 4 .3 thickness of 1.6mm. The length of the anten na i s t he p arameter that controls t he resonant f requency. As res ult, th e length is treated as half wave dipole, which is given by the following for mula: 2   L (1) F C   (2 ) Where L is d ipole length, λ is the wa velength, C is the speed of light in free space and F is t he freque ncy of operation [3 ]. Table 1 shows the range of the dimensions para meters and table 2 presents the calc ulated values. TABLE I D ESIGN R ECOMMENDATION A ND R ESTRICTION [2] Parameters Symbol Recommendatio n Restriction Width ( W)   1 . 0 05 . 0   W 20 05 . 0   h w Length ( L)  48 . 0  L 5 . 0  W T Height ( H)  02 . 0  h 5 . 0  h T Thickness ( T)   T 1  r  TABLE II C ALCAULATED V ALUES O F A NTENNA P ARAMETERS Material Type mm L- mm w- mm h- mm FR4 4.3 2.65 104 52 6.25 2.08 Arlon AD300 3 2 118 59 7.08 2.36 Rogers RT5880 2.2 1.6 132 65.88 7.92 2.64 However, the speed of the signal when it pr opagates i n free space varie s as it propagates in medium a nd that is bec ause of the effective dielectric constant of the microstrip substrate associated with fringing fie lds [4]. Therefore, the ab ove equations have b een modified to the following: (3) (4) (5) In most pr actical d esign, t he wavele ngth o f t he printed dipole is treated as appr oximately in medium with equivalent to the a verage of that in free space, which is considered as alternative method for better determination of the length. Besides, th e antenna par ameters diff er widely for different types o f material s [5]. The feeding method i s desi gn ed using integrated microstrip balu n. Planar antennas ar e inte grated with other micro wave circuitry. T herefore, the feeding techniques need to be designed and analyzed properl y to reach b etween a good antenna per formance and ef ficient circuit design. T he word balun is a narro wing for “balanced to unbalanced” [ 5]. Table 3 has the practical p arameters of the antenna bei ng designed . At 1 800 MHz band the anten na wavelength is 89.9 mm given by ( 3), the co rresponding resonant length is 67 mm for dipole with open st ub and 60 mm for dipole with via -hole b y (4) and (5). Fig . 1 shows the open stu b feeding while Fi g. 2 ill ustrates the dipole antenna with via-hole feed. Fig. 1. Dipole with quarter w avelength open stub fee d Fig. 2. D ipol e wi th V ia-hol e fe e d TABLE III D IMEN SIONS O F Q UART ER W A VLENGTH A ND V IA - HOLE Parameter Specifications PCB Substrate FR -4, h=1.6mm , =4.3, tanδ= 0.00 2. Di pole arm L= 67mm, W =6mm, gap g = 3mm Microstrip Balu n L= 22mm, L =3mm, w=5mm, w = 3mm Ground Plane L = 25mm, w= 15mm. Feed Line L=25mm, w =3mm, Open stu b=25mm Dipole arm Length L = 60mm, Width W= 6mm, ga p g = 3mm. Vi a-hole R= 0.375mm I II. P RINCIPLES O F B ALUN O PERATION A ND D ESIGN The main obj ective of balun design is to pro vide the syste m with balance transition between t he antenna and its feeding circuit. Ho wever, as the rest of t he syste m was then overturned as o ne part o f ant enna at tached to ex ternal plate while th e other connec ts to the interna l connector . On the edge attac hed to t he sh ield, th e current ca n pass t hrough o ver the outside o f the coa xial cabl e. Baluns cha nges t he te nt o nto the antenna po rts the same magnitude o n each but acro ss stage, these te nsions ca used t he same a mount of current flow to the outside of the coaxial cable. T his type of arra ngement will let the feed point to have the same phase as the point of the top shield [6]. Fig . 1 shows quarter wavelength open st ub feeds t he dipole strips by cr eating virtual short circuit acro ss the ce nter of t he dipole. This arrangement pr ovides further p ossibilities for reactance compens ation of the balance load [7]. The speci al feature of this m ethod is that it does not require phy sical direct connection top of subst rate. Therefore, it is commonl y used to feed micro strip dip ole ante nna bec ause it requires no soldered or plated through connection [8 ]. IV . S IMULATION R ESULT A. Quartered wavelength open stub metho d The result sho ws the s -parameter as function of frequen cy. The p lot of S11 shown in F ig . 3 is used to determine whether the antenna i s a single ban d and operating at the desire d resonant frequency also the band width can be calculated fo r   f c  4 3   L 3 2   L the cor responding freq uency band. It provides band width o f 17% of the res onance freq uency with maximum ret urn los s o f -47.88 dB as sho wn in Fig. 3. Fig . 4 il lustrates how t he resonant freque ncy is shifted down as the length reduces while T able 4 is a sum mary of the resulting measure ments of different lengths. The balance f eeding is illustrated by the value of VSWR in Fig. 5 while F ig . 6 sho ws the radiatio n pattern of the antenna. TABLE IV C OMPARISON F OR D IFFERENT L ENGTHS A T W= 6 mm Length Z11 VSWR RL BW Directivity 63mm 45 -i 4 1.1013 -26dB 16% 1.7dB 65mm 48 - i 2.2 1.05 -32dB 16. 5% 1.8dB 67mm 51 - i0.216 1.0081 -47.dB 17% 2dB Fig. 3. Return L oss Plot at 1800 MHz of antenna Fig. 4 Return L oss for diffe rent lengths of the di pole Fig. 5. VSWR of feeding circ uit Fig. 6. Dire ctivity in the Azimuth pla ne B. Via-hole feed ing method The dipole radiator is modeled on the top of s ubstrate a nd adopted with the integrated b alun to form a ground plane as a return bath for the current dis tributions. Since this feedi ng is through via from the to p to the bottom ph ysically co nnecting the feed line to the center of the dipole to make the for mation of center fed the simulations results di ffers for differ ent widths of t he a ntenna a nd T able 5 summarize t he differences as well as F ig . 8. Besides, the antenna is resonating at 1.8GHz as shown i n F ig . 7 with sufficient balance between antenna and its feeding circ uit which is d etermined by the value of VSWR i n F ig . 9. From F ig . 1 0 , it can be seen that the antenna has omnidirectional rad iation pattern. TABLE V C OMPARED R ESULTS F OR D IFFERENT W IDTHS Width Impedance VSWR Return Loss Bandwidth % 8mm 43.614 1.255 -18.95dB 24.5% 7mm 44.43 1.216 -20.22 dB 22.5% 6mm 45.3 1.18 -21.6 dB 20.6% 5mm 46.17 1.17 -22.74 19.7% Fig. 7. Return L oss 1800MHz of antenna Fig. 8 . Return L oss for different w idths of the antenna Fig. 9. VSWR of t he fee d circuit Fig. 10. Directivity of the dipole antenna Since the polarization of the antenna is horizontal, the E- plane co incides with the a zimuth pla ne and the H -field coincides with elevation pla ne as sho wn i n F ig . 11 and Fig. 12. T he ne w feat ures in this design in compar ison to previous research works is that it ha s planar structure which ca n easi ly integrated to ar ray form to provide greater d irectivity and high e fficiency witho ut cau sing substantial p ower lo sses in the feeding circ uit si nce eac h element i s matc h to its feedi ng circuit impedance. In term of bandwidth, this antenna has bandwidth range fro m 1 8.4% to 25% while previous sear ch has band width fro m 1 1.53% to 13.22%[3]. T his advantage is a result of choosing the ri ght configuration o f the feeding circuit. Fig. 11 . E-field Ra diation at 1.8G Hz Fig. 12 . H- field Radia tion at 1.8G Hz V. DISCUSSI ON Throughout the en tire simulation r esults it ha s been seen how t he ante nna performance behaves as function of its geometry para meters. Besid es, the feedin g tech nique is important factor t hat make s substantial effects on t he simulation results. First, the dipole with integrated via-hole balun feed is being used as balance to unbalanced tr ansform er and impe dance transformer from co axial line to the two pr inted dipoles strip via physical co nnection. This method is capab le to pro vide us with a bandwidth of 18.4% W ith maxim um return loss of - 25dB as shown in F ig . 8 at length =59 mm , width=4 mm and height=1.6 mm . the bandwidth can be increased to 2 4.5% by changing the width o f the antenna from 4mm to 8mm . However, the size w ill increase and other im pacts such as reducing the return loss and increasing the value of VSWR. In ter m of practical implementation, it is considered o ne of the most common suitable due to its compact size and acceptable performance b ut it requires soldering which may cause junction radiation. The second part is about open stub in tegrated balun. This method does not require dir ect co nnection between the feed line and the dipo le. Therefore, a virtual short circuit is created between the open stub and the dipo le strip making a ce nter fed current distribution [ 7] . The optimized dimension for op timu m p erformance are at length=65 mm , width=6 mm and height=1.6mm. The optimum results are bandwidth of 17 per cent with minim um VSWR1.008 v also maxim um return loss o f -47. 88dB. T he radiation p attern o f this method is unidirectional and has main lobe directivity of 2 dB in the elevation plane with angular width of 8 9 deg and has the same magnitu de on the az imu th plane. For implem entation, it is very co nvenient and suitable since it does not require soldering though it has narrow bandwidth but ag ain it depends o n the application requirements. V. C ONCLUSI ON This pr oposed work focu ses on the design a nd simulatio n of planar d ipole antenna for 1800MHz Band for GSM application using CST studio software. The antenna was structured o n FR4 substrate with relati ve constant of 4.3 . Two types of feeding con figuration have been designed to feed the antenna in order to match 50 ohm transmission line. These types are via -hole integrated balu n, and quarte r wavelength o pen stub. As results, the di mension of the antenna and simulatio n results such as r eturn loss, band widt h and volta ge standing wave ratio (VSWR) has b een a nalyzed . For instance, the via-hole is capable to provide max imum return loss o f -25 dB, band width of 18 .4% and VSWR of 1.116 v at length of 59 mm and width 4 mm; it is b andwidth can be i mproved to 25% an d 30%. While the open stub at length o f 67 mm, width of 6mm a nd height 1.6 mm can provide max return loss of -47.88 dB and bandwidth of 17% with VSWR 1.00 8 << 2 and also has better radiation pattern. R EFERENCES [1] Balanis C. A.. 2005 .Antenna theory Analysis and d esign , 3 rd edition. Wileterscience p ublication 3 rd . ISBN: 0 - 471 - 66782- x. [2] Garg, R ., Bhartia, P ., Bahl, I. & Ittipiboo n, A. 2001. 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