SEI 9 5 th Intenational Coneence: Sciences o Electonic, echnologies o Inomation and elecommunications Mach -6, 9 UNISIA A Modiied Bow ie Antenna o FID Application Abdelhak FECHICHI*, Noueddine SBOUI* and Ali GHASSALLAH* *Unité de echeche Cicuits et Systèmes d électoniques Haute Féquences, Faculté des sciences de unis, unisie abdelhakechichi@yahoo. noueddine.sboui@st.nu.tn ali.ghasallah@gmail.com Abstact: his pape coves the design and optimization o new antenna o FID applications at micowave equencies. he stuctue is designed to esonate at.45ghz one o the FID equencies. he new patch is inspied om Bow ie antenna and it epesents a eduction o the size by moe than 8% compaing to monopole patch with an acceptable gain and diectivity. An equivalent esonant model is pesented based on a model o tiangula antenna. Simulation esults given by ou appoach, show that the antenna and its model have the same esonant equency at.45ghz but with a little dieence in Bandwidth. Key wods: adio Fequency Identiication FID, AG, eadable ange, and Bow ie Antenna. INODUCION adio Fequency Identiication is an automatic identiication technology o objects. he FID system is made up o a eade and a ag which is attached to objects. he identiication does not necessitate a contact between the eade and the tag. he antenna is the main component o FID system. It epesents the channel between the eade and the tag igue (1). As FID equencies aise into micowave egion, the antenna should be caeully designed in ode to educe the tag size and to maximize the tanse o powe into and out o the tag [AMI 7]. hus, we should in choosing the antenna consideate some points. Fist, the type o the antenna should die om the eade to the tag and om an application to anothe. Second, the antenna should be small, easy when made and cheap when poduced. hid, the F chaacteistics o the antenna should be acceptable consideing impedance, gain and diectivity. On the one hand, the eduction o the size o the antenna means a possibility to have a small AG which can be placed anywhee without occupying a lage place. On the othe hand, one o the impotant chaacteistic o FID system is the eadable ange. he eadable ange is the maximum distance that the Inteogato can ead om the AG. his distance depends essentially on the gain o both the AG antenna and the eade antenna as shown in the equation 1 [KLA 3]: = λ 4π PG 1. 4 eade P 3. G (1) Figue 1. FID system With: P3 = Powe eceived in the AG P1 = Powe tansmitted by the Inteogato G eade = he Gain o inteogato antenna G = he Gain o AG antenna In this pape, we popose a new small tag antenna. - 1 -
SEI9 he patch is based on a bow tie antenna. It simulated using ADS. he impotance o the new patch is that we educe the oiginal antenna size that esonates at.45ghz by moe than 8%. In ode to validate ou wok, we simulated an electical model o the stuctue and we compae the ADS esults o the physical patch. 1. A bow tie small antenna 1.1. Geomety o tiangula antenna Figue () shows the geomety o an equilateal tiangula micostip patch on a dielectic substate with a gound plane. he antenna is mounted on a substate mateial with a thickness h=3.mm, a dielectic constantε =.6 and loss tangent (tangδ) =.. Figue. iangula Antenna stuctue 1.. Electical model o tiangula patch he ecent study wok o micostip patch have demonstate that the tiangula patch have a adiation chaacteistic simila to a ectangula patch but with a educed dimensions [NAS 4]. Fo this eason, to studies ou antenna, we can eplace the tiangula electical model by its equivalent electical ectangula model igue (3). o calculate the model paametes, we use the omula pesented in [CEL 98] to evey tiangle. Z Z in in = + j X () - = + j X - 1+ - 1 + - esonant esistance : L he esonant esistance is calculated using equation (3) as in [CEL 98]: = cos (3) H π ε ε A : esonant equency : uality acto ε : amic pemittivity π x a x : the distance o the eed point om the edge o the patch. a : length o tiangle H : thickness o dielectic A : aie o tiangle 1 1 1 1 = + + (4) C D c ε = : adiation quality acto (5) 4 H 1 D = : losses in the dielectic (6) gδ ( ).786 Z a W H C= : losses in the conducto (7) P a Figue 3. Electical model o iangula antenna W ε 1 +.441+.8 + 6π H ε Za ( W ) = ε ( ε + 1 ) W 1.451 Ln.94 + + πε H is the impedance o an ai illed micostip line ( ) = (, ε = 1) Z W Z W a a (8) - -
SEI9 W W ( π H ) H π + 1 H W + +.94 W H Pa = W W + Ln π exp.94 H π + H, W > H ε C = C ( ε ) ( ε ) (9) (1) ( ε, HW, ) ( = HW) εε A 1 εe εε A C ( ε) = + (11) H γγ n m γ n cz ε 1,, H 1, j= γ j =, j ( w 377 ) ZwH (,, 1 H ε = ) = Ln 1 (1) π + + w W h H.758 3.666 = 6+ 6 exp (13) H W H ( w ) ( π ) Capacitance C, Inductance L: o detemine the capacitance C we use the omula o. C o detemine L, we know that: Figue 4. etun loss o both physical and model o tiangula patch 1.3. Geomety o poposed bow tie antenna he poposed patch is constituted o ou tiangle patches disposed on plana stuctue igue (5). his stuctue is inspied om the bow tie patch antenna. Only one tansmission line links the ou tiangles. he patch is mounted on a dielectic with a thickness h =.65mm and pemittivityε =,3. Inductive eactance o Coax: Inductive eactance o Coax is calculated via the equation below: he model is simulated and then compaed to physical patch. he esults ae epesented in igue (4). he tiangula patch and its electical model pesent a esonant equency about.45ghz but with a dieence in Band width because o the dieence between calculated and simulated losses. he gain and diectivity equal espectively 7.41dB and 7.81dB. Figue 5.Poposed bow tie antenna stuctue - 3 -
SEI9 1.4. Electical model o analyze this antenna, an electical model is developed. he model is inspied om the electical model o tiangula patch descibed by Nasimuddin and A. K. Vema in [NAS 4] whee they eplaced the tiangula patch by its equivalent ectangula patch and then they built the tiangula electical model. he tansmission line is also modelled by an LC cicuit. he electical model is epesented in igue (6). Figue 7. etun loss o both physical and model o poposed bow tie antenna Figue 6. Electical model o poposed bow tie antenna he LC paametes ae calculated using the omulas developed in section 1.. esults and discussion.1. Dimensions he poposed patch is designed to esonate at.45ghz (one o the FID equencies). he odinay dimension o an antenna is about 6cm 6cm. he dimension o the pesent antenna is about 1.6mm 6.3mm which means that the dimensions o antennas ae educed by moe than 8%. Hence we can obtain a vey small tag with a good chaacteistic... etun loss he etun loss is shown in igue (7). he esonant equency is.45 GHz. he antenna epesents a band width about 8 MHz which is acceptable to FID system. he magnitude S11 attainted 5dB..3. Gain and Diectivity As the eadable ang depends on and diectivity, we should guaantee suitable ones. Fo ou poposed bow tie antenna, the gain and the diectivity ae successively 1.6dB and 4.87dB which ae acceptable paametes to an FID system. Finally, when we compae physical patch and electical model we can see that the esonant equency is the same and thee is a little dieence in band width due to the dieence in losses between theoy and eal. 3. Conclusion he eduction o antenna and tag size is o geat inteest o many applications. In this way, many techniques ae applied to popose a vey small patch. On the one hand, in this pape we think that educing antenna size by moe than 8% is vey impotant. On the othe hand, amelioating antenna paametes and deceasing antenna cost ae ou pioities in ou utue eseach. EFEENCES [AMI 7] Ami Galehda, David V. hiel, and Steven G. O Keee Antenna Eiciency Calculations o Electically Small, FID Antennas, IEEE Antenna Wieless Popagation Lettes, Vol 6, pp 156-159, 7 [KLA 3] Klaus Finkenzelle, FID HANDBOOK, Second Edition, 3-4 -
SEI9 [NAS 4] Nasimuddin and A. K. Vema Ami, Fast and accuate model o analysis o equilateal tiangula patch antenna, Jounal o Micowaves and Optoelectonics, Vol 3, pp 99-11, Apil 4 [CEL 98] Celal YILDIZ, Keim GÜNEY, Simple model o the impedance o ectangula micostip antenna, jounal o engineeing sciences, pp 733-738, 1998-5 -