Design of Ultra Wideband Antennas in the Form of Planar Electric or Magnetic Monopoles

Transcription

1 Design of Ulta Wideband Antennas in the Fo of Plana Electic o Magnetic s A. M. Abbosh (), M.E. Bialkowski (), () School of ITEE, Univesity of Queensland, Qld. 407, Austalia abbosh@itee.uq.edu.au Abstact An efficient appoach to design ulta wideband (UWB) antennas in the fo of plana electic and agnetic onopoles is pesented. Siple design foulas fo this type of adiatos ae descibed and thei validity is tested via full electoagnetic analysis with Ansoft High Fequency Stuctue Siulato (HFSS). In the pesented exaples, Low Tepeatue Cofied Ceaic (LTCC) in the fo of thick DuPont95 ateial is assued as the antenna substate. The pesented esults show that using this substate, vey copact UWB antennas can be developed. Siulations using HFSS pove the high accuacy of the poposed design ethod. The designed antennas featue nea onidiectional chaacteistics and good adiation efficiency.. Intoduction Recent yeas have witnessed an inceased inteest in ulta wideband (UWB) antennas since the adoption of UWB technology by US-FCC in 00 which assigned the fequency band of GHz fo UWB applications []. It is envisaged that UWB can bing significant advances paticulaly in wieless counications as a eedy to the existing fequency spectu congestion. In addition to solving the spectu congestion poble, UWB has potential to delive high data ate tansission. In paallel to developing UWB technology ecent eseach has been focused on educing the size of font end odules in wieless tansceives by using ulti-laye low tepeatue co-fied ceaic (LTCC) stuctues []. Many wieless systes have aleady discoveed the benefits of LTCC technology. This is because it can not only delive exteely sall package size but also offes good electical pefoance, high eliability, excellent theal stability, supeb unit to unit epeatability, and low cost. The usual equieent fo a wieless equipent is that the font end has to be connected to a adiating eleent, antenna. This ceates a challenge to the designe when the font end is developed in LTCC. The eason is that it is not easy to connect o electoagnetically couple a sepaate antenna to the LTCC cicuit. The ethod poposed and investigated in this pape is to use the uppe layes of the LTCC to build the antenna. In ode to achieve an UWB pefoance a nube of antenna candidates can be investigated. Fist, the designs utilizing a adiating eleent being pependicula to the gound plane [3] have to be discaded. The eason is that they ae unsuitable fo integation with LTCC. As a esult, only plana UWB antennas need to be consideed. Those include a plana volcano-soke slot antenna [4], a coplana waveguide fed bowtie/tiangula patch antenna [5], a ulti-stuctue coplana waveguide (CPW) fed [6], a ulti-esonance plana patch antenna [7] and a pinted onopole [8]. Elliptical and cicula adiating eleents to fo plana UWB antennas have been epoted in [9-0]. The ain shotcoing of the designs of these plana UWB antennas is that they ae based on the tial and eo ethod. In ode to obtain an optial design, coputationally intensive full wave electoagnetic siulations ae usually applied. Howeve, when one decides to obtain an antenna with a siila pefoance using a diffeent dielectic substate, the tie consuing design pocess has to be fully epeated. This is not welcoe by designes, which do not have access to sophisticated EM analysis and design softwae packages. This pape addesses this shotcoing by poviding siple design foulas which ae suitable fo UWB antennas in the fo of plana onopoles fed fo a icostip line. The diffeence between values of the design paaetes, i.e. diensions of antenna stuctue, is less than 0% copaed to the optiu values that ae obtained using the coecial softwae Ansoft HFSS. Section of this pape descibes the poposed design ethod and section 3 pesents esults of siulation using Ansoft HFSS while section 4 concludes the pape.

2 . Design Configuations of the UWB antennas, which ae investigated hee, ae pesented in Fig.. The stuctues shown in Fig.a and b ae identified as plana electic onopoles. These ae ceated by a plana conducting suface foed by the intesection of eithe two ellipses o two cicles in a two-side conducto-coated substate. In these stuctues, the suface electic cuent flowing on an elliptical o cicula shaped conducto is egaded as the piay souce of adiation. In tun, the stuctues shown in Fig.c and d ae copleentay to those in Fig. a and b and ae naed hee as plana agnetic onopoles. In these stuctues, the electic field (o its suface agnetic cuent equivalent) in an elliptical o cicula shaped slot is egaded as the piay souce of adiated field. The use of the tes of electic and agnetic onopole, which ae intoduced hee, equies an exta explanation. The eason is that these piay adiatos ae accopanied by the pesence of a tapeed slot, which is ceated between the uppe conducto and the gound plane. This slot plays a consideable ole in obtaining wideband pefoance. It can be egaded as soe fo of a tapeed slot antenna whose boadband opeation is govened by the size of its opening. This opening has to be about half-wavelength at the lowest fequency of opeation. As a esult of this explanation it becoes appaent that both the shape of electic / agnetic onopole and of the tapeed slot is esponsible fo boadband opeation of the intoduced antennas. Hee, we pesent siple design foulas to achieve boadband opeation of the adiating stuctues of Fig. ad. We coence this pocess with the assuption that a icostip line feeding these stuctues is chosen to be with diensions ealizing 50- Ω chaacteistic ipedance. In addition, we assue that the size of the gap (g) between the onopole and the gound plane is siila to the icostip line width. Input ipedance is only slightly sensitive to this paaete and hee g is chosen in the ode of. The eaining design steps ae suaized as follows. ) Depending on the lowest fequency of opeation ( ), thickness of the substate (h) and its dielectic constant ( ε ), width ( w ) and length (l ) of the antenna stuctue including the feede can be calculated [] ; c w = f ε + c l = l f ε e f () () ε + ε h 0.5 e = + [ + ] w ( ε e + 0.3)( w/ h) l = 0.4h ( ε 0.58)(0.8 + w / h) ε (3) e whee c is speed of light in fee space and ε e is the effective dielectic constant. We will assue that w is extended along the x-axis while l is extended along the y- axis. As we ae in the peliinay stage of the design then the paaete l is neglected as it has usually a sall value assuing that w/ h >>. ) The adiating slot is foed by the intesection of two ellipses (o cicles) in the anne shown in Fig.. The seconday diaete of the ellipses, o the diaete of the D D cicles ( & ) and atio of the seconday diaete R R to the ajo diaete in the two ellipses ( & ) in the peliinay stage of the design ae equal to; (4) D = w (5) D = w/ (6) R = R 0.5 (7) = Equations (5) and (6) indicate that the peliinay D D values of and ae chosen to be copaable to half and quate of the effective wavelength, at the lowest fequency of opeation, espectively. 3) Centes of the two ellipses o the two cicles ae shifted by a cetain distance fo cente of the gound plane in ode to get the best atch to the 50 Ω feede. Pats of the two ellipses that extend outside the gound plane fo one diection ae cut. 4) The gound plane in all cases is in the shape of a half ellipse whose diaete and atio of its seconday to piay adius D 3 R 3 D 3 ae chosen as; C = (8) f ε e R = (9) w 5) Width of the icostip tansission line, to give chaacteistic ipedance Z equal to 50 Ω can be calculated using the following equations []; o

3 fo fo Z 60 8h w = ln( ) (0a) ε w 4h o + w Z o w e / h, and = ε [ w e / h, whee 0π / h ln( w (0b) / h+.44)] ε e is the effective dielectic constant fo the tansission line and it is given by; ε + ε e = + () * ε + h / w In ode to deonstate the validity of the above pesented foulas, we pesent a nube of designs assuing an LTCC substate in the fo of DuPont95 ateial with ε =7.8, tangent loss=0.005 and thickness=. Paaetes fo UWB slot antennas obtained with the above pesented foulas ethod, as well as the optiized values ae shown in Table assuing a.5ghz value fo ( ). The optiization was pefoed fo the best ipedance bandwidth with nea onidiectional chaacteistics. The pesented values show that the designed UWB antennas can be of vey copact size, which is advantageous in applications equiing vey copact RF font ends. 3. Results The siulations of the fou configuations of UWB antennas wee pefoed with Ansoft HFSSv9. on a PC with dual Xeon.8GHz pocessos and 3.5GB of RAM as a siulation platfo. Radiation boxes used with HFSS to plot the adiation patten and easue gain had diensions in the x, y and z diections oe than a quate wavelength (at the lowest fequency of opeation) away fo the antenna stuctue [3]. Figue shows vaiation of the etun loss with fequency fo the fou designed antennas. The obtained esults indicate that the designed antennas have UWB chaacteistics with an ipedance bandwidth which coves the UWB fequency band assuing a 0dB etun loss efeence. Fo the UWB applications point of view the antenna is usually equied to have an onidiectional adiation. This equieent is fulfilled ove the whole bandwidth as shown in Fig.3 fo the elliptical electic onopole. Siila esults wee obtained fo the othe designed antennas. Gain of the designed antennas is evealed in Fig.4. It vaies between about 0.5dB to 4.7dB ove the equied bandwidth fo the electic onopoles while it is between - 0.5dB to.5db fo the agnetic onopoles. These esults f indicate that the electic onopoles show a highe gain copaed to thei agnetic counte pats. Using a substate with a high dielectic constant and a diect icostip feede ay cause deteioation in the adiation efficiency of the antenna. To check this case, vaiation of the suface efficiency with fequency fo the designed antennas was calculated with HFSS softwae. These calculations have shown that the designed antennas have always a good efficiency which is geate than 9%. 4. Conclusions In this pape, a siple ethod fo designing plana UWB antennas in the fo of plana electic o agnetic onopoles has been pesented. In the chosen configuations, the adiating stuctue is foed by the intesection of two ellipses o two cicles. Fo an electic dipole, an electic cuent flowing on the conducto foing the onopole is esponsible fo adiation. In tun, in a agnetic dipole, an electic field in a slot pefos a coplientay function. Copute siulations have shown that the poposed design foulas povide UWB antenna diensions which diffe by less than 0% fo the optiized ones. The designed antennas cove the band allocated to UWB systes with well behaved onidiectional adiation patten and oe than 9% adiation efficiency. 5. Refeences [] New public safety applications and boadband intenet access aong uses envisioned by FCC authoization of ulta-wideband technology-fcc news elease (Febuay 4, 00) ( Gov /Bueaus/ Engineeing_Technology/ News_Releases/00/net003.pdf) [] C. Baatt, LTCC integated font end odules, in IEEE MTT-S Syp. Wokshop, Pape WME09, 000. [3] T. Taniguchi and T. Kobayashi, An onidiectional and low VSWR antenna fo the FCC-appoved UWB fequency band, Antennas and Popagation Society Intenational Syposiu, 003. IEEE Volue 3, -7 June 003, pp [4] J. Yeo, Y. Lee and R. Mitta, Wideband slot antennas fo wieless counications, IEE Poc.- Micowave antennas and Popagation, Vol.5, No.4, Aug.004, pp [5] N. Fotino, G. Kossiavas, J. Dauvignac and R.Staaj, Novel antennas fo ulta-wideband counications, Micowave and Optical Technology Lettes, Vol.4, 004, pp [6] S.Lee,J.Pak and J.Lee, A novel CPW-fed ultawideband antenna design, Micowave and Optical

4 Technology Lettes, Vol.44,No.5, Mach005, pp [7] M.Ala and M.Stuchly, Multiesonance plana patch antenna, Micowave and Optical Technology Lettes, Vol.46, No., July005, pp [8] S.K.Padhi et al., Investigations into pinted onopole antennas fo ulta-wideband (UWB) applications, Poc. 005 Intl IEEE AP-S Syp., Washington, D.C., 3-8 July 005. [9] J.Liang, C.Chiau, X.Chen and C.Paini, Pinted cicula disc onopole fo ulta-wideband applications, Electonics Lettes, Vol.40, No.0, Sept.004, pp [0] C.Huang and W.Hsia, Plana elliptical antenna fo ulta-wideband counications, Electonics Lettes, Vol.4, No.6, Mach 005, pp [] C.Balanis, Antenna theoy; Analysis and design, John Wiley & Sons Inc., Thid edition, 005. [] D. Poza, Micowave Engineeing, John Wiley & Sons Inc., Thid edition, 005. [3] S. Rousselle, A detailed eview of HFSS v9 pots and bounday conditions, 003 HFSS Uses Wokshop, Ansoft Copoation, 003. (a) (b) (c) (d) Fig..Configuations of the fou designed UWB antennas. The adiating eleent with the feede is on the top laye while the half ellipse gound plane (GND) is on the botto laye.

5 Design Paaete TABLE Calculated and optiized values of design paaetes in (). Values calculated using foulas Optiized Elliptical Electic Optiized Cicula Electic Optiized Elliptical Magnetic Optiized Cicula Magnetic w l D D w g Retun Loss[dB] Elliptical Electic Elliptical Magnetic Cicula Electic Cicula Magnetic Feq[GHz] Fig.. Vaiation of etun loss with fequency fo the designed antennas.

6 Fig.3. Thee diensional adiation patten fo the elliptical electic onopole at diffeent fequencies. 5 4 Peak Realized Gain[dB] 3 Elliptical Electic 0 Elliptical Magnetic Cicula Electic Cicula Magnetic Feq[GHz] Fig.4. Vaiation of the peak ealized gain with fequency fo the designed antennas.