DESIGN AND PARAMETRIC EVALUATION OF RECTANGULAR MICROSTRIP PATCH ANTENNA FOR GSM APPLICATION RAHUL T. DAHATONDE, SHANKAR B. DEOSARKAR Dept. of E & TC, D. Babasaheb Ambedka Technological Univesity, Lonee, 402 103, Tal. Mangaon, Dist. Raigad, INDIA. http://www.dbatu.ac.in Abstact This pape discusses design and paametic evaluation of Rectangula Micostip Antenna (RMSA) fo GSM Communication. A simple RMSA is designed using tansmission line model and analyzed using Method of Moment (MoM) based softwae IE3D fo studying its behaviou with vaious paametes such as, its length, width, height of substate, location of feed position, effect of substate dielectic constant and effect of finite gound plane. It was obseved that the theoetical esults obtained using IE3D ae in good ageement with measued esults pesented in liteatue. Keywods Rectangula Micostip Antenna, paametic study. 1. Intoduction These days, MSAs ae widely used in many applications due to thei inheent advantages such as low pofile, light weight, plane configuation and ease of fabication. Theefoe, thee is lot of eseach going on in design and development of MSAs suitable fo vaious communication engineeing applications. In this pape, we have designed a simple RMSA using tansmission line model. This RMSA is analyzed using Method of Moment (MoM) based softwae IE3D fo studying its behaviou with vaious paametes such as, its length, width, height of substate, location of feed position, effect of substate dielectic constant and effect of finite gound plane. 2. Design of RMSA [1 2] The basic RMSA is a stip conducto of dimensions L x W on a dielectic having dielectic constant and thickness h backed by a gound plane. Fo RMSA width is compaable to wavelength to enhance adiation fom edges. The substate thickness is much smalle than the wavelength, theefoe RMSA is consideed to be 2D plana configuation fo analysis. Fields associated with MSA ae divided into inteio and exteio egion as shown in Figue 1-a. Inteio egion is fomed by the patch, potion of the gound plane unde patch and walls fomed by the pojection of the patch peiphey onto gound plane. Exteio egion is fomed by est of the space which includes emainde of gound plane, emainde of dielectic, and top of the patch conducting suface [2]. The fields in the inteio egion can be modeled as a tansmission line section. This gives ise to designation tansmission line model (TLM). Fields in the exteio egion compise of adiation field, suface waves, and finging field. The chaacteistic impedance Z and the popagation constant 0 j, fo the line ae detemined by the patch size and substate paametes. The peiphey of the patch is descibed by fou edges which ae classified as adiating type o non-adiating type depending on the field vaiation along thei length. Field vaiation along adiating edge is 2 and it s constant along width (non-adiating edge) [1]. TLM epesents MSA by 2 slots sepaated by a tansmission line as shown in Figue 1-b. The micostip sepaates two dielectics, i.e. substate and ai. Hence most of the electic field lines eside in the substate and some extend to ai. This tansmission line cannot suppot pue TEM mode of popagation since the phase velocities would be diffeent in the ai and the substate. Hence, effective dielectic constant must be obtained in ode to account fo finging fields. The value of effective dielectic constant is less than dielectic constant of the substate, because the finging fields aound the peiphey of the patch ae not confined in the dielectic substate, but ae also spead in the ai. ISSN : 0975-5462 Vol. 5 No.01 Januay 2013 123
Figue 1-a. RMSA field distibution [2] Figue 1-b TLM epesentation of RMSA [1] The value of this effective dielectic constant is given by [1], eff 1 1 12h 2 2 2 1 W whee, is effective dielectic constant and eff, h, W epesent dielectic constant, height and width of the substate, espectively. Fo RMSA to be an efficient adiato, W should be taken equal to a half wavelength coesponding to the aveage of the two dielectic mediums (i.e., substate and ai) [1] c W 1 2 f 0 2 Fo the fundamental TM 10 mode, the length L should be slightly less than 2, whee is the wavelength in the dielectic medium. Hee, 0 eff whee is the fee-space wavelength and 0 eff is the effective dielectic constant of the patch. Fom the voltage and cuent distibution shown in Figue 2-a it is clea that, voltage is maximum and cuent is minimum along the width of the patch due to the open ends. Theefoe, the input impedance of the RMSA vaies fom zeo value at its cente to the maximum value (180-Ω) at its adiating edges. Electomagnetic field lines at the edges as shown in Figue 2-b can be esolved into nomal and tangential components with espect to gound plane. 1 Figue 2-a. Voltage and Cuent distibution Figue 2-b E-field distibution The nomal components of E-field at the two edges along the width ae in opposite diections and thus out of phase since the patch is 2 long and hence they cancel each othe in boadside diection. The tangential components ae in phase; hence the esulting fields combine to give maximum adiated field nomal to the suface of the stuctue. Hence edges along the width can be epesented as two adiating slots, 2 apat and excited in phase and adiating in half space above the gound plane. The finging fields along the width can be modeled as adiating slots inceasing electical length of patch than physical length. This incease in length is given as, ISSN : 0975-5462 Vol. 5 No.01 Januay 2013 124
L 0.412h Thus at esonance fequency, effective length of the patch is, W 0.3 0.264 h W 0.258 0.813 eff eff h c Le L 2L 2 f whee, c is velocity of light in fee space. The actual length of the patch, L can be detemined fom above equation. Fom these equations, a RMSA was designed to opeate ove GSM fequency of 1.8 GHz. The optimized length and width of the RMSA was found to be 39 mm and 51 mm, espectively. This RMSA was simulated using Zeland s MoM based EM Simulation Package, IE3D [3]. Fo simulations, the FR4 substate with dielectic constant of 4.47 with thickness of 1.59 mm was consideed. 3. Paametic Study of RMSA The RMSA designed in ealie section was analyzed using softwae IE3D fo studying its behaviou with espect to vaious paametes such as feed point location, width and length of the patch, height, loss tangent and dielectic constant of the substate, diamete of feeding pobe and size of gound plane. 3.1 Effect of feed-point location As discussed above, the input impedance of the RMSA vaies fom zeo value at its cente to the maximum value (180-Ω) at its adiating edges. The feed-point should be located on the patch at a point whee input impedance is 50-Ω at esonance fequency. The cente of the patch is taken at oigin and feed-point location is given by coodinates (X f, Y f ) with espect to oigin. Thee exists a point along the length of the patch, whee RL is minimum [4]. In ode to locate optimum location of feed point, etun loss is calculated using IE3D at diffeent locations on the patch and a point whee RL is most negative is selected as a feed-point. Figue 3-a, -b show the cuves obtained fo etun loss and VSWR Vs fequency at diffeent feed locations. It is seen that the minimum value of RL, -34.24 db, occus at feed location (10.8, 0). VSWR at this point is 1.03. Theefoe, this is consideed as optimum feed point location. 0 eff Fig. 3-a. Retun Loss Vs Fequency at diffeent feed locations Fig. 3-b. VSWR Vs Fequency at diffeent feed locations Figue 3-c shows Smith Chat obtained at diffeent feed locations. It is seen that as X f inceases fom 10 mm to 11.6 mm (i.e., the feed point is shifted towad the edge of the patch), the input impedance loci shifts in the ight diection on the Smith chat implying that the impedance is inceasing. It can be emembeed that impedance at the cente of the patch is 0 Ω and at edges it is 180 Ω. The 2D adiation patten of RMSA obtained at feed location of (10.8, 0) shows that HPBW in E- and H-plane is 105 and 76 degees espectively and diectivity is 6.4 db. Thus it is clea that feed location (10.8, 0) is the optimum feed location fo this RMSA at 1.8 GHz. Its vaious pefomance paametes ae summaized in following table: Feed location Retun loss VSWR Diectivity Bandwidth Input Impedance (10.8, 0) -34.24 db 1.03 6.4 db 50 MHz (49.39 j1.80) Ω ISSN : 0975-5462 Vol. 5 No.01 Januay 2013 125
Fig. 3-c. Smith Chat at diffeent feed locations Fig. 3-d. 2D Radiation Patten at feed point (10.8, 0) 3.2 Effect of patch width To study the effects of change in width of patch on its pefomance, its width vaied fom 30 mm to 70 mm, keeping the feed-point location same fo all simulations at (10.8, 0) with espect to oigin. It is obseved that width of the patch has significant effect on BW, gain and input impedance of the RMSA. Figue 4-a and b shows the cuves fo etun loss and VSWR Vs fequency, fo diffeent values of width of patch. Fom Figue 4-a, it is seen that, BW inceases with incease in width of patch, howeve, RL deceases. The minimum value of RL, 34.24 db, occus only fo designed width of 51 mm, indicating pefect match of MSA with feed line. Fig. 4-a. Retun Loss Vs Fequency fo diffeent values of width of patch Fig. 4-b. VSWR Vs Fequency fo diffeent values of width of patch Also esonance fequency deceases fom 1.84 GHz to 1.79 GHz, with incease in W fom 30 mm to 70 mm, because width is invesely popotional to esonance fequency. Similaly, fom Figue 5-b, it is seen that VSWR at esonance fequency of 1.8 GHz is 1 only fo designed width of 51 mm. Howeve, effects of change in width of the patch on pefomance of MSA can be studied bette, if feed-point is optimized fo each design. Also, with incease in width of patch, the adiation fom the adiating edges incease, theefoe the adiation esistance deceases esulting in decease in input impedance. This is appaent fom the Smith Chat shown in Figue 4-c, fo diffeent values of width of patch. Apetue aea of MSA inceases with incease in width, causing gain to incease, since gain is diectly popotional to apetue aea. Fo W=70 mm, diectivity is 6.62 db, which is slightly bette than diectivity at designed width of 51 mm. The HPBW in H-plane deceases but in E-plane is almost constant since beamwidth inceases in H-plane. ISSN : 0975-5462 Vol. 5 No.01 Januay 2013 126
Fig. 4-c. Smith Chat fo diffeent values of width of patch Fig. 4-d. 2D Radiation Patten fo diffeent values of W = 70 mm Thus with incease in width of patch, BW, diectivity and gain incease, howeve, esonance fequency and input impedance decease. 3.3 Effect of height of substate A substate in MSA is pincipally equied fo the mechanical suppot of the antenna metallization. A thicke substate besides being mechanically stong, will incease the adiated powe, educe conducto loss and impove impedance BW. Howeve, it will also incease weight, dielectic loss, suface wave loss, and extaneous adiations fom the pobe feed. These effects ae simila to decease in substate dielectic constant [2]. Resonance fequency, BW, gain and input impedance of RMSA wee studied fo incease in h. Fom the RL Vs fequency cuve in Figue 5-a, it s seen that, with incease in h fom 1.59 mm to 3.18 mm esonance fequency deceases fom 1.8 GHz to 1.76 GHz. Because, with incease in h, the finging fields fom the edges incease. This inceases the extension in length L and hence the effective length, theeby deceasing the esonance fequency. Also, esonance feq educes fom 1.8 GHz to 1.76 GHz and BW inceases to 62MHz, with incease in h. Fig. 5-a. Retun Loss Vs Fequency fo diffeent values of height of substate Fig. 5-b. VSWR Vs Fequency fo diffeent values of height of substate Smith Chat shown in Figue 5-c, shows that with incease in h, input impedance cuve moves clockwise (i.e., an inductive shift occus), because coaxial feed pobe length inceases, inceasing inductance. On the othe hand with the incease in h, the W/h atio educes which deceases effective dielectic constant and hence inceases the esonance fequency. Howeve, the effect of the incease in L is dominant ove the decease in effective dielectic constant. The 2 D adiation patten in Figue 5-d, shows that the diectivity of the antenna inceases maginally to 6.6 db, because the effective apetue aea is inceased slightly due to incease in L. ISSN : 0975-5462 Vol. 5 No.01 Januay 2013 127
Fig. 5-c. Smith Chat fo diffeent values of height of substate Fig. 5-d. 2D Radiation Patten fo h = 3.18 mm Thus with incease in height of substate, BW and diectivity of MSA inceases but esonance fequency deceases. Howeve, input impedance becomes moe inductive. 3.4 Effect of substate dielectic constant A low value of will incease the finging field at the patch peiphey and thus the adiated powe. An incease in h has simila effects on antenna chaacteistics as decease in [2]. Thus incease in h o decease in will incease the adiated powe, educe conducto loss and impove impedance BW. VSWR, input impedance and etun loss chaacteistics wee studied fo thee diffeent values of. Figue 6-a. Retun Loss Vs Fequency fo diffeent values of substate dielectic constant Figue 6-b. Smith Chat fo diffeent values of substate dielectic constant Fom RL Vs fequency cuve shown in Figue 6-a, it is seen that when is deceased fom 4.4 to 1, the esonance fequency inceases fom 1.8 GHz to 3.6 GHz. ISSN : 0975-5462 Vol. 5 No.01 Januay 2013 128
Figue 6-c. VSWR Vs Fequency fo diffeent values of substate dielectic constant Figue 6-d. VSWR Vs Fequency fo substate dielectic constant = 1 Thus with decease in, BW and esonance fequency incease and input impedance becomes moe inductive. 3.5 Effect of pobe diamete An RMSA can be fed with diffeent types of connectos, such as SMA, TNC, and N type, depending upon the application. The diametes of these connectos ae diffeent. Input impedance and VSWR plots fo two diffeent connectos, with d = 1.2 mm and 4 mm ae obseved. As the pobe diamete inceases, the pobe inductance deceases fo the same substate thickness. With an incease in the pobe diamete, the esonance fequency inceases slightly (Figue 7-a) and the pobe inductance deceases causing the impedance plot to move in the anticlockwise diection (Figue 7-b). Figue 7-a. Retun Loss Vs Fequency fo connectos with diffeent diametes Figue 7-b. Smith Chat fo connectos with diffeent diametes 3.6 Effect of finite gound plane Fo all the simulations and measuements discussed in ealie sections, we have consideed RMSA with infinite gound plane, because the tansmission line model is based on assumption of infinite gound plane [1]. Howeve, in pactice, MSAs ae designed and fabicated with gound plane of sufficiently lage size but still this is not infinite. It is poved in [1] that when the size of the gound plane is geate than the patch dimensions by appoximately six times the substate thickness all aound the peiphey, the esults ae simila to that of the infinite gound plane. Thus fo this RMSA, the length and width of finite gound plane ae calculated as, 47.76 mm and 60.22 mm, espectively. Fom RL and VSWR cuves in Figue 8-a and -b, espectively, it is obseved that the esonance fequency of the RMSA fo finite and infinite gound plane is almost the same. ISSN : 0975-5462 Vol. 5 No.01 Januay 2013 129
Fig. 8-a. Retun Loss Vs Fequency with finite and infinite gound plane Fig. 8-b. VSWR Vs Fequency with finite and infinite gound plane Howeve input impedance with finite gound plane is slightly highe than with infinite gound plane (Figue 9- c). The 2-D adiation patten shown in Figue 9-d, indicates that thee ae back lobes pesent with finite gound plane, wheeas thee ae no back lobes with infinite gound plane. Theefoe, diectivity with finite gound plane is less. Figue 8-c. Smith Chat with finite and infinite gound plane Figue 8-d. 2D Radiation Patten with finite gound plane It was obseved that softwae IE3D assumes infinite gound plane by default since it s based on Method of Moment (MoM) which consides only infinite gound plane. Theefoe, duing simulations, with infinite gound plane, softwae pefoms meshing only on adiating patch and simulates it. Theefoe, the simulation time fo RMSA with infinite gound plane is small compaed to RMSA with finite gound plane. 3.7 Effect of loss tangent Substates having a low dielectic loss ae expensive. Fo initial testing o fo designing new MSA configuations, sometimes low-cost substates ae used, but geneally these have lage tan value [1]. Hence, it is impotant to know the effect of tan on the pefomance of the antenna. VSWR and input impedance of the designed RMSA was studied fo thee diffeent values of tan (0.0001, 0.01 and 0.02). Fom RL and VSWR Vs fequency cuves in Figue 9-a and b, show that with an incease in tan fom 0.0001 to 0.02, the esonance fequency emains almost the same. In Figue 10-b, fo tan = 0.0001 thee is no point coesponding to VSWR 2, theefoe BW appeas almost zeo. Howeve, with an incease in tan, the losses in the patch incease leading to an incease in BW, which is aound 50 MHz fo tan = 0.02. Due to incease in loss tangent, the losses in the dielectic mateial incease theefoe input impedance deceases, shifting the impedance plot towad the left side Figue 9-c. ISSN : 0975-5462 Vol. 5 No.01 Januay 2013 130
Figue 9-a. Retun Loss Vs Fequency fo diffeent values of tan Figue 9-b. VSWR Vs Fequency fo diffeent values of tan Howeve, 2 D adiation patten and hence diectivity fo diffeent values of tan emains almost the same. Thus with an incease in tan, BW inceases, input impedance deceases and diectivity emains the same. Figue 9-c. Smith Chat fo diffeent values of tan Figue 9-d. 2D Radiation Patten fo tan =0.0001 3.8 Effect of dielectic cove MSAs ae sometimes coveed with a dielectic laye to potect them fom the envionment, o painted with dielectic mateial. The dielectic laye influences the chaacteistics of the antenna and, in geneal, educes the esonance fequency due to incease in the effective dielectic constant [5]. Effect of dielectic cove with =4.4, on VSWR, etun loss and input impedance of patch was studied fo diffeent values of height of supestate, i.e. h 1 = (0, 1.59, 3.18, 4.77). Figue 10-a. Retun Loss Vs Fequency fo diffeent values of Figue 10-b. VSWR Vs Fequency fo diffeent values of ISSN : 0975-5462 Vol. 5 No.01 Januay 2013 131
As seen fom the RL and VSWR plots shown Figue 10-a and b, with incease in supestate thickness fom 0 mm to 4.77 mm, the esonance feq deceases fom 1.8 GHz to 1.71 GHz. Also incease in supestate thickness implies that the loss in the dielectic mateial and hence input impedance deceases, so the impedance plot shifts towad the left side. Conclusion In ode to study pefomance of RMSA with change in vaious paametes such as, its length, width, height of substate, location of feed position, effect of substate dielectic constant and effect of finite gound plane, an RMSA was designed using tansmission line model and analyzed using Method of Moment (MoM) based softwae IE3D. It was obseved that the theoetical esults obtained using IE3D ae in good ageement with measued esults pesented in liteatue. Refeences [1] Kuma G. and Ray K.P., Boadband Micostip Antenna, Atech House, London, 2003. [2] Gag, I. Bahl, A. Ittipiboon, and P. Bhatia, Micostip Antenna Design Handbook, Atech House, London, 1980. [3] IE3D 12.0, Zeland Softwae Inc., Femont, CA, USA, 2008. [4] C. Balanis, Antenna Theoy Analysis & Design, John Wiley & Sons, 2nd Ed., 1997. [5] I. J. Bahl, et.al., Design of Micostip Antennas Coveed with Dielectic Laye, IEEE Tans. Antenna Popagation, Vol. 30, 1982, pp. 314-318. [6] Bhatia P., Millimete-Wave Micostip and Pinted Cicuit Antennas, Atech House, London. Autho Biogaphy Rahul T. Dahatonde, eceived his B. E. and M. Tech. degees in Electonics & Telecom. Engineeing in the yea 2001 and 2003 fom Noth Mahaashta Univesity, Jalgaon and D. B. A. Technological Univesity, Lonee, espectively. He is cuently pusuing his Ph.D. fom D. B.A.T.U., Lonee in the aea of Micostip Patch Antennas. His eseach inteests include antennas, micowaves and EMI/EMC. He has published aound 10 eseach papes in vaious intenational and national jounals/confeences. He is life membe of ISTE, India. D. Shanka B. Deosaka eceived M.Tech. and Doctoate Degee in the aea of Micowave Communication in the yea 1990 and 2004, espectively fom S.G.G.S. Institute of Engineeing and Technology, Nanded. Cuently, he is a Pofesso of Electonics & Telecommunication Engineeing at D. B. A. Technological Univesity, Lonee. He is having aound 21 yeas of expeience in academics. He has about 50 eseach publications to his cedit at the National and Intenational level. At pesent he is guiding fou Ph. D. Reseach Scholas in the aea of Optical Communication and Micostip Antenna Design. He had deliveed invited talks at vaious Indian and foeign Univesities such as McGill Univesity, Monteal, Canada, Electomagnetic Reseach Cente, Ottawa, Govenment of Canada and Pinceton Univesity, New Jesey, USA. He has successfully caied out vaious Govt. funded eseach pojects in the aea of Communication Engineeing and EMI / EMC. ISSN : 0975-5462 Vol. 5 No.01 Januay 2013 132