Design and Measurements of a Quasi-isotropic UWB Planar Antenna

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Desig ad Measuremets of a Quasi-isotropic UWB Plaar Atea Atoie Diet, Nicolas Ribière-Tharaud To cite this versio: Atoie Diet, Nicolas Ribière-Tharaud.

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1 Desig ad Measuremets of a Quasi-isotropic UWB Plaar Atea Atoie Diet, Nicolas Ribière-Tharaud To cite this versio: Atoie Diet, Nicolas Ribière-Tharaud. Desig ad Measuremets of a Quasi-isotropic UWB Plaar Atea. Recet patets o Electrical Egieerig, 211, 4 (3), pp <1.2174/ >. <hal-64128> HAL Id: hal Submitted o 17 Nov 211 HAL is a multi-discipliary ope access archive for the deposit ad dissemiatio of scietific research documets, whether they are published or ot. The documets may come from teachig ad research istitutios i Frace or abroad, or from public or private research ceters. L archive ouverte pluridiscipliaire HAL, est destiée au dépôt et à la diffusio de documets scietifiques de iveau recherche, publiés ou o, émaat des établissemets d eseigemet et de recherche fraçais ou étragers, des laboratoires publics ou privés.

2 Desig ad Measuremets of a quasi-isotropic UWB micro-strip atea Atoie Diet, Nicolas Ribière-Tharaud Laboratoire des Sigaux et Systèmes / Départemet de Recherche e Électromagétisme L2S/DRÉ UMR 856 (CNRS-Supélec-Uiversité Paris-Sud-11) Supélec, 3 rue Joliot Curie, plateau du Moulo F Gif sur Yvette, Frace atoie.diet@lss.supelec.fr Abstract This paper summarizes the desig ad measuremets of a quasi-isotropic prited UWB atea, with the aalysis of its performaces through defied figures of merit. State of the art gives the opportuity to exploit some empirical cosideratios about the shape ad the methodology of coceptio. A simple structure is simulated by meas of CST Microwave Studio to show the possibility of fulfillig, at a defied level, UWB atea requiremets such as matchig, fidelity ad quasi-isotropy of the radiatio patter with a simple micro-strip desig ad a stadard techology. The desig of this atea is based o cosideratios about bulbous ad beded travelig wave ateas. Results of its characterizatio i aechoic chamber are quatified i terms of amplitude ad phase variatio, i order to illustrate the level of dispersio for the differet directios. I - INTRODUCTION ABOUT UWB ANTENNAS I the cotext of wireless local ad mobile etworks, UWB commuicatios systems are a iterestig solutio to avoid the problem of stadards co-existece ad iterfereces [1]. The immuity of such systems is based o the widebad ad low power pulses trasmissio. We focus herei o UWB commuicatio systems that are based upo 3-11 GHz ateas. The goal is to trasmit very low power pulses i order to achieve sufficiet data rate without disturbig other eighborig wireless commuicatios that share part of the UWB bad. Ateas dedicated to such applicatios are ot supposed to be multi-harmoic but they are required to be really o-dispersive ad widebad. Power matchig should be realized cotiuously o the whole 7.5 GHz wide frequecy bad. Furthermore, the phase trasfer respose must be liear with respect to frequecy ad ideally for ay directio of emissio, as mobility cosideratios require UWB ateas to be as isotropic as possible. Both frequecy ad time domai resposes must be cosidered durig the desig. The dispersio that ca be observed o radiated pulses reveals the atea time behavior. Itegratio ad productio of UWB mobile trasceivers imply a additioal task that cosists i buildig a miimum-size low-cost atea. These cosideratios lead to avoid volumetric structures (i.e., bicoical, 3D moopoles or hors). However studyig the latter as possible UWB ateas is essetial to fid desig rules for other techologies. Micro-strip atea shapes, for example, are ofte ispired by projectio of 3D existig ateas. I short, itegratio of a UWB atea requires the latter to be isotropic (almost) ad matched over a wide bad ad to show a miimum size, a low cost ad a low dispersio (cotiuously). UWB atea property, i their fudametal idea, provides a variatio i amplitude i phase that should ot destroy a sigal usig the whole badwidth cotiuously: a pulse. This is poited out because lots of widebad atea are i fact multi-arrowbad oes. As a cosequece, the differece betwee widebad ad impulse widebad property lie i the time domai aalysis. Desigig this type of atea is ot a recet challege ad this is proved by the importat state of the art (bicoical, hor ) [2]-to-[15]. Iterest is i the time domai approach ad the ew techical cosideratios such as itegrated atea ad o more 3D structures. The goal is to reduce the size for a potetial itegratio of a UWB commuicatio system for mobility ad coectivity applicatios. We focused o prited bulbous travelig waves ateas, i order to avoid reflexio ad multi-resoat structure. A widebad resoatig solutio would drive it to a cripplig effect of rigig, geeratig time dispersio of the pulse i the time domai uless the atea is matched. We favored the quasi isotropic ad dual polarizatio property by reducig the groud plae (this icreases the sesibility also). This was justified i the way that this atea is supposed to be used as a eergy detector. A potetial applicatio of such a atea ca be the trasmissio of BAN (Body Area Network) sigals, i the cotext of omadic sesors etworks. II - STATE OF THE ART AND FIGURES OF MERIT As reported by Schatz [1], the iterest i widebad ateas is old. History begis with bicoical 3D ateas. It goes o with hors ad spherical fat structures with iterestig widebad properties [1]. I 194, Kigs claims that fatter is better, arguig that the stored reactive eergy is reduced i bulbous atea [2, 3]. The, a lot of work has bee doe o volumetric curve based or tapered atea. Frequecy idepedet ateas, based oly o agles, were studied by Rumsey [12]. This was the itroductio of spiral ad log-periodic ateas, although the latter are dispersive due to phase cetre traslatio i frequecy. Nowadays, moder UWB ateas have to accout for several cosideratios: matchig properties, miimum reactive power

3 ad resoace (which leads to thick or bulbous structures), low cost ad small size (which lead to prited ateas). Several techologies ca be used to realize widebad ateas [1][5][1][8]. May authors cosider plaar moopoles ad slot lie ateas [5, 9]. The most importat costrait is to build a o-resoat structure, which geerally implies wide bet surfaces of coductor, prited o substrates. Travelig wave structures are also preferred because they are ot subject to geometric resoaces. This causes the success of the Vivaldi atea [8] despite its directioal radiatio patter. Cosiderig practical realizatio requiremets (size ad cost), the prited atea is very popular for UWB. The geometry is first desiged for a wide radiatio patter ad, the, optimized for frequecy matchig. Figure 1 displays two cofiguratios summarized i [8]: The rig tapered slot ad the hor type prited atea. These solutios offer good matchig ad radiatio patters for several tes of square millimeters. Refereces [5] ad [6] preset slot ateas ad moopoles that are matched i a secod step by a modificatio of the geometric parameters. It seems that thick prited structures offer the widebad behavior ecessary for UWB i a first step, bet shapes beig chose to radiate with large beam-width ad groud plae beig avoided to eable isotropic radiatio. The secod step is to cosider both matchig ad dispersio. These empirical cosideratios have bee accouted for i the simulatio of the bet elliptical moopole described i the ext part. I x ( ) ( ( )) max ( x) mi ( x) si ϕmi( x) si ϕmax x = (3) 4π The lower the factor I x for a give level x, the better is our atea for isotropy cosideratios. I fact, this factor correspods to the area (expressed i str.) where the radiated power level is less tha x dbi, ormalized with respect to the area correspodig to a referece isotropic atea radiatig x dbi, i.e., 4π str. For time domai aalysis, we use the defiitio of fidelity, derived from [9] ad expressed by equatio (4). As it is clearly uderstood, the fidelity quatifies the time pulse correlatio, for oe directio of radiatio, compared to the ideal oe, i.e., the feedig sigal (ofte a Gaussia pulse, or oe of its derivatives). ( ϕ) F, R = Rxx xy( τ) ( ) R ( ) yy max ( τ) x :ideal pulse with y :radiated pulseat (, ϕ) These three figures of merit: 2.log 1 S 11, I x ( f ) ad F (,ϕ), will help atea desigers to qualify UWB atea simulatios or measuremets. As expressed i [11], a UWB atea must be based o several cosideratios: wide badwidth, fixed phase-cetre over frequecy, high radiatio efficiecy, low cost ad small size. Other properties such as polarizatio ad feedig techiques are cosidered i fuctio of the trasmissio chaels. (4) Figure 1 : Half-rig tapered slot (left) ad hor type (right) prited UWB ateas reported i [8] I order to aalyze the results i the frequecy ad time domais, we use differet figures of merit. Matchig is characterized by meas of retur loss (RL) calculatio as a S 11 f i db. For the radiatio fuctio of the frequecy: ( ) patter (RP), the observatio i a 2D projectio eables us to idetify gaps (whose locatios, i spherical coordiates, are idicated by limits i adϕ ) that severely impact o the atea isotropic properties. We propose to characterize isotropy by meas of a isotropic factor I defied at oe frequecy ad for a referece level x (expressed i dbi). The factor I is as follows: N Radiatio Patter Areas I I (1) [ db i ] = x x ϕ max ( x ) max ( x ) 1 I x = cos( ϕ) ddϕ 4π (2) ϕ mi ( x ) mi( x ) III - SIMULATIONS OF A SIMPLE PRINTED STRUCTURE A. Atea descriptio The structure is a bet micro-strip elliptical moopole, simulated uder CST microwave studio. Its dimesios are 8 mm 6 mm ad the substrate is a Rogers RT588 (ε r = 2.2) with a mm thickess ad a 7 µm thick copper coductor (that correspods to stadard realizatio values). The feed is doe by meas of a matched micro-strip lie with taper, the width varyig for matchig optimizatio. It is supposed to be directly coected to a 5 Ω lie or a HF coector. The desig ad photography is depicted i figure 2. The idea is to favor curret flowig o a wide area ad the isotropy is supposed to be iflueced by the bedig of the ellipse. The ellipse eccetricity ad circular taper size were firstly optimized for matchig o the whole badwidth (1.log 1 S 11 < -1 db). I a secod step the curvature was icrease to geerate à radiatig field i differet directio of the space. The agle was stopped at 18 to avoid a aular resoatig pheomeo that would have caused a rigig effect, source of time dispersio. The limitatio of the groud plae eables the radiatio i a «more» isotropic maer, ad the resultig polarizatio is circular due to the curret flowig.

C. Results of the simulatio: radiatio patters agle THETA i agle degrees 15 1 5 5 1 15 2 25 3 35 Φ agle PHI agle i degrees 4 GHz MAX 4.

4 C. Results of the simulatio: radiatio patters agle THETA i agle degrees Φ agle PHI agle i degrees 4 GHz MAX 4.2 dbi 6 dbi agle THETA i agle degrees PHI agle Φ agle i degrees 6 GHz MAX 6.6 dbi Figure 2 : Simulatio ad prited atea desiged B. Results of the simulatio: retur loss The first desig criterio is to adapt the structure to 5 Ω o the 3-11 GHz bad. Figures 3 ad 4 display the fial result, after a geometrical optimizatio. Figure 3 displays the behavior of the S 11 parameter versus the frequecy; the adapted 5 Ω poit ca be clearly see at the cetre of the trajectory. Figure 5 shows the retur loss value: it is below - 1 db, which correspods to a classical limit for atea adaptatio. agle THETA i agle degrees agle THETA i agle degrees PHI agle Φ agle i degrees PHI agle Φ agle i degrees 8 GHz MAX 6.4 dbi 1 GHz MAX 4.1 dbi - 2 dbi Figure 5 : 2D maps of the radiatio patter at 4, 6, 8 ad 1 GHz: the scale covers from -3 db to db with respect to the maximum value idicated o the right. Radiatio patters at 4, 6, 8 ad 1 GHz are reported i figure 5: they are displayed i the (, ϕ) plae correspodig to the agles used i equatios (1), (2) ad (3). This Figure illustrates atea directivity. Some holes appear i directios ( = 9, ϕ = 25 3 ) ad ( = 9, ϕ = 2 5 ). The radiatio patter is very omi-directioal: the radiated field shows a gai ear dbi over a very large part of the space. This ca be cofirmed by computig the isotropy factor I at differet levels of gai. 5 Figure 3 : S 11 parameter polar plot from 3 to 11 GHz S 11 i db I x i % of total radiated solid agle GHz I -6 dbi I -9 dbi 15 I -1 dbi Frequecy i GHz Figure 4: S 11 atea parameter Frequecy i GHz Figure 6: I x as a fuctio of the frequecy (x = -6, -9, -1 dbi)

5 Figure 6 displays the factor I (at x = -6, -9 ad -1 dbi) as a fuctio of the frequecy. For example, at a level x of - 9 dbi, the area where the radiated power is less tha P rad -9 db represets less tha 12% of the total area (where P rad is the power radiated by a ideal isotropic source). The behavior of the atea radiatio patter reveals selectivity ear 5 GHz; elsewhere the atea radiates power i almost all directios. The quasi-circular ature of the polarizatio is depicted i figure 7, which also displays the right ad left polarizatio radiatio patters Table 1: Locatio, orietatio ad fidelity results of probes Positio agles i degrees (radius = 1m) Théta () Phi (φ) Orietatio vector Fidelity to emitted pulse 76.2 % φ 87.3 % 9.5 % φ 96.2 % 85.6 % φ 79.8 % 83.7 % φ 69.2 % 85.4 % φ 94.1 % 82.8 % φ 89.8 % 84.4 % φ 77.1 % 84.5 % φ 71.8 % 77.6 % φ 9.8 % 68.1 % φ 92. % 5. % φ 9. % 88.8 % φ 98. % Figure 8 displays a compariso betwee the three worst results (i italics) ad the best (98%) ad referece oes Emitted pulse Figure 7: Atea (top left) ad axial ratio of the radiatio patter at 4 GHz (top right). Lower row: left (blue) ad right (red) polarisatio radiatio patters as fuctios of (ϕ =, 4 GHz). D. Results of the simulatio: Fidelity The fidelity is computed by simulatig the respose of liear probes, at a distace of 1 meter ad for differet positios. Spherical coordiates are used i Table 1, as i the paper. At each positio, observatio is performed by meas of two liearly polarized probes orieted i the directios of the vectors ad ϕ respectively. It ca be oticed that oly three directios show fidelity lower tha 71%. For the latter, the fidelity computed at the same positio but for the other orietatio is almost 8%. This meas that it is always possible to improve the fidelity thaks to the orietatio of probes at these locatios. I figure 8, the best case for the fidelity is obtaied with a shift of 18, which is the reaso why the pulse appears as iverted. This is ot damagig for a correlatio receiver % Fidelity Received pulse ( = 45, φ = 45 ) φ Time i ao-secodes 68.1 % Fidelity Received pulse ( = -13, φ = ) x Time i ao-secodes x % Fidelity Received pulse ( = 13, φ = -45 ) φ Time i ao-secodes 5. % Fidelity Received pulse ( = -45, φ = ) x Time i ao-secodes Figure 8: Normalized pulses at differet agles (, ϕ). The three worst results (top right ad lower raw) are compared to the best ad referece oes (top left) i terms of fidelity. At ay locatio, it is possible to reach more tha 83%, depedig upo the orietatio. These results allow us to argue about the dispersio of the atea: the latter seems to bee ot so destructive, from the pulse shape poit of view. The modificatio of the pulse by the radiatio is ot the same x 1-9

i differet plaes. Radiatio patter ad matchig performaces give the opportuity to optimize the desig i accordace with dispersio properties. Fidelity results cofirm the potetial of this atea for UWB.

6 i differet plaes. Radiatio patter ad matchig performaces give the opportuity to optimize the desig i accordace with dispersio properties. Fidelity results cofirm the potetial of this atea for UWB.. IV - MEASUREMENTS OF THE ANTENNA The atea was maufactured ad measured. Due to the process tolerace ad the small groud plae, the width of the impedace lie ad taper slightly varies ad geerate a shift i frequecy, as see i figure 9. We thus reitroduce the variatio i the simulator ad the badwidth retro-simulated is 5-12 GHz. The small size of the groud plae implies a high sesitivity of this atea, as the figure 1 cofirms this. This ca be see as a drawback but the reductio of the groud plae eables the possibility of isotropy characteristic. Icrease of this groud plae would result i the reductio of the isotropy factor. This would be logically doe for omidirectioal atea desig. db -1 db simulatio I Figure 9, type 2 ad type 3 ateas correspod to improvemets such as eccetricity ehacemet (+2%) for type 2 ad additio of a coupled circular patch o the oradiatig face for type 3. These modificatios act as badwidth ehacemet due to the icrease of the propagatio surface, respectig the priciple of travelig wave (prited) ateas. Trasmissio measuremets were doe thaks to the spherical far-field test facility SESAME i Supelec (LSS- DRE) as represeted i figure 1. Due to the legth of the cables (almost 1 meters), a LNA (.2-18 GHz Mitech, +3 db medium gai, +3 db Noise Factor) was added to improve the measuremet dyamic, uless the additio of oise. This is ecessary because a isotropic atea has gai i the rage of dbi. The PNA8753 used caot evaluate the reflectio coefficiet of the system due to the system cripplig losses at GHz frequecies. After calibratig the trasmissio with a referece probe, the S 21 parameter is extracted. Results of the RP are show i figure 11. The gai varies from +6 dbi to -2 dbi i this figure. The directivity of the atea is very sesitive to the groud plae due to the large radiatig area. Figure 11 shows the quasi-isotropic ad widebad behavior of the atea because the top views are plotted at 1, 11 ad 12 GHz. 1 GHz radiatio patter DDR pour ue fréquece de 1 GHz 11 GHz radiatio patter DDR pour ue fréquece de 11 GHz 12 GHz radiatio patter DDR pour ue fréquece de 12 GHz -2 db -3 db 6 GHz 1 GHz mesure type 1 type 2 type Frequecy i GHz Figure 9: (retro-) Simulatio (top) ad S 11 measuremets (bottom) dbi 6 dbi Figure 11: measured RP at 1, 11, ad 12 GHz. S 21 measuremets are used to evaluate the efficiecy of the atea (de-embeddig of the probe cotributio). The efficiecy is computed for the two polarizatios, figure 12. These results are i good agreemet with the measured retur loss of the atea, figure Overall efficiecy Motors - 1) Probe azimut - 2) Probe polarisatio - 3) Rotatio S(f,,φ) PROBE LNA.5.4 Efficiecy for plae AUT PNA GHz Efficiecy for φ plae Ffrequecy (Hz) x 1 9 Figure 1: S 21 parameter measuremets i SESAME Figure 12: Efficiecy thaks to the RP measuremets.

7 Trasmittig ad receivig UWB impulse sigal implies the atea S21 parameter, i ay directio (, ϕ ), to be as ivariat as possible i amplitude ad phase over the largest badwidth. Dispersio ad compressio would result i the destructio of the pulse shape ad decrease the fidelity at a cripplig level. Thaks to the measuremet platform, we computed statistically the umber of directios (5 o 5 solid agle step) for which S 21 ( f,, ϕ ) has - a miimum superior to 1 dbi a miimum to maximum level variatio iferior to 1, 13 ad 16 db. For differet frequecy badwidths of iterest: 3-1, 3-5, 4-6, 6-8, 6-12 ad 8-13 GHz. Results are reported figure 13. The variatio reported i figure 13 reveals a amplitude distortio o the trasmitted pulse. S21 variatios eable to idetify the worse case of the atea ifluece over a give badwidth. A high sesitivity with the polarizatio i the plae is show. This ca be related to the o-symmetry of the atea. The phase variatio is also de-embedded from measuremets ad reported i figure 14 for the two polarizatios vectors. These results drive us to limit the maximum variatio to ± 1 degrees betwee 1 ad 15 GHz. This measure is importat for studyig the worst case impact of such ateas i UWB impulse radio systems. MAX-MIN < 1 db MAX-MIN < 13 db MAX-MIN < 16 db MIN > -1 db -2 Polarisatio Polarisatio φ Polarisatio Polarisatio φ Polarisatio Polarisatio φ Polarisatio Polarisatio φ 3 1 GHz 11 % 3% 24 % 8% 41 % 18 % 12 % 1% 3 5 GHz 54 % 41 % 72 % 57 % 83 % 7 % 27 % 13 % 4 6 GHz 63 % 45 % 77 % 61 % 86 % 72 % 46 % 13 % 6 8 GHz 56 % 38 % 7 % 53 % 78 % 67 % 47 % 21 % 6 12 GHz 21 % 7% 37 % 16 % 52 % 3 % 28 % 4% 8 13 GHz 34 % 14 % 54 % 3 % 66 % 43 % 37 % 8% x x 1 Statistical over 249 directio (5 step) "3-1 GHz case (-1dB)" Figure 13: Statistical results for the amplitude variatio i fuctio of the directio Phase dispersio (i degrees), polarizatio /φ x 1 Frequecy i GHz x 1 Frequecy i GHz Figure 14: Phase respose i degrees for the two polarisatio vectors ( o the left, ad φ o the right. Red curves is the de-embedded respose of the LNA, coected to the referece hor atea probe. Coclusio The atea desiged i this paper is based o the applicatio of major priciples o widebad (travellig waves) isotropic ateas. The adaptatio from 3D volumetric to 2D prited structure is achieved as the compariso betwee simulatios ad measuremets is satisfyig. Usig this type of atea for impulse radio is possible as the fidelity is importat ad the amplitude ad phase variatios are i acceptable rages. As the atea is desiged for isotropy ad ot oly omi-directivity, its RP is difficult to measures ad its EM sesitivity is high. This is due to the weak differece betwee

8 atea gais i the differet directios. S 21 coefficiets are measured for a prited low cost prototype atea ad give some referece values for reitroducig the propagatio chael i the performace evaluatio of a wireless UWB commuicatio system. REFERENCES [1] M. Ghavami, L. Michael ad R. Khoo. UWB sigals ad systems i commuicatios egieerig Wiley 24. [2] H. Shatz. A brief history of UWB ateas Proceedigs of IEEE UWB Systems ad Techologies, 23. [3] H. Shatz. Radiatio efficiecy of UWB ateas Proceedigs of IEEE UWB Systems ad Techologies, 22. [4] R. Schmitt. Uderstadig electromagetic fields ad atea radiatio takes (almost) o math EDN mag., N 3 2, pp [5] M. A. Peyrot-Solis ad al. State of the Art i UWB Ateas 2 d Iteratioal Cof. o Electrical ad Electroics Egieerig (ICEEE), Mexico, Sept. 25. [6] H. Schatz. Dispersio ad UWB Ateas IEEE Ateas ad Propagatio Symposium 5, 25. [7] H. Schatz. A ear field propagatio law ad a ovel limit to atea gai Vs size IEEE Ateas ad Propagatio Symposium, 25. [8] D. C. Cheg. Update various kids of UWB ateas IEEE UWB Symposium 25, Taïwa. [9] T. Ma, S. Jeg. Plaar miiature tapered slot fed aular slot ateas for UWB radios IEEE trasactios o Ateas ad Propagatio, N 3, 25 pp [1] H. Schatz. The Art ad Sciece of UltraWideBad Ateas Artech House, 25. [11] R. Scholtz ad al. Ultra-Widebad Radio EURASIP Joural o Applied Sigal Processig, March 25, pp [12] V. Rumsey. Frequecy idepedet atea IRE Natioal Covetio Record, pt. I, 1957, pp [13] W. Sörgel et al. Optimizig atea performace for UWB impulse systems EuCAP 26. [14] K. Cha et al. A Novel CPS-fed Balaced Widebad dipole for UWB applicatios EuCAP 26. [15] R. Serrao et al. Small atea fudametals ad techologies : future treds EuCAP 26.

A New Design of Log-Periodic Dipole Array (LPDA) Antenna

A New Design of Log-Periodic Dipole Array (LPDA) Antenna Joural of Commuicatio Egieerig, Vol., No., Ja.-Jue 0 67 A New Desig of Log-Periodic Dipole Array (LPDA) Atea Javad Ghalibafa, Seyed Mohammad Hashemi, ad Seyed Hassa Sedighy Departmet of Electrical Egieerig,