Design of a Planar Slotted Waveguide Array Antenna for X-band Radar Applications

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1 JOURNAL OF THE KOREAN INSTITUTE OF ELECTROMANETIC ENINEERIN AND SCIENCE, VOL. 11, NO., JUN. 11 JKIEES DOI : /JKIEES Design of Plnr Slotted Wveguide Arry Antenn for X-bnd Rdr Applictions Rshid Ahd Bhtti 1 Byeong-Yong Prk 1 Yun-Tek I Seong-Ook Prk 1 Abstrct A plnr slotted wveguide rry ntenn hs been designed t 9.37 Hz for X-bnd rdr pplictions. The ntenn consists of ultiple brnchline wveguides with brodwll rditing shunt slots nd in wveguide to feed the brnch wveguides through series of inclined coupling slots. The ntenn feed point is locted t the center of the in wveguide. Eleent weights in the rry hve been clculted byspling continuous circulr Tylor perture distribution t the 5 db sidelobe level in both the E nd Hplnes. A coercilly vilble electrognetic (EM) siultion tool hs been used to chrcterize the individul isolted slot nd tht dt hssubsequently been used to design the plnr rry. The rry is finlly nlyzed in CST Microwve studio nd the esured nd siulted results hve been found to be in good greeent. Key words : Antenn, Slot, Wveguide. Ⅰ. Introduction Slotted wveguide rry ntenns re widely used for rdrs nd couniction systes [1]. They offer significnt dvntges in ters of weight, volue, nd rdition chrcteristics. These ntenns re very ttrctive due to their plnr, copct, nd rugged construction. A etllic wveguide is low loss structure nd it cn hndle high power. The diensions of the slots in the wveguide wlls cn be controlled to relize the desired pttern shpe. Longitudinl shunt slot rrys re lso ttrctive due to their very low cross-polriztion levels. The design of resonnt slotted wveguide rry ntenn is generlly bsed on the procedure published by Elliot [] [4]. In these design procedures, inter-slot distnce is one-hlf the guide wvelength nd the wveguide end is short circuited t distnce of qurter-guide wvelength fro the center of the lst slot. Liner rrys re plced djcent to ech other to relize plnr rrys. A feed wveguide is plced beneth the brnch wveguides contining rditing slots nd power is coupled fro the in wveguide to the brnch wveguides through the series of inclined slots. The feed wveguide is terinted in the short circuit locted t distnce of one-hlf of the guide wvelength fro the center of the lst inclined coupling slot. Externl nd internl utul coupling effects cn be fully incorported into the design procedure. Other jor reserch works onliner nd plnr slotted wveguide ntenns re [5], [6]. Isolted slot chrcteriztion is required in the design of slotted wveguide rrys. Isolted slot dittnce cn be esured experientlly [] or coputed nuericlly [7] [9]. Cre ust be exercised in clculting the individul slot dt s inor errors ight severely ffect the overll rry design. In this pper, the design of plnr slotted wveguide rry ntenn bsed on the procedure in [3] is discussed. The design procedure includes bothexternl utul coupling effects nd internl utul coupling using coercil EM siultors to pproch ore exct results. The plnr ntenn hs been designed t 9.37 Hz with shunt slots cting s rditorsin the brodwll of reduced height wveguide to suppress higher odes. The plnr rry consists of twelve liner rrys of shunt slots, which hve been plced side-by-side with truncted corner slots to fit the ntenn in circulr boundry. A in wveguide is run cross the brnch wveguides to feed the through the inclined-series coupling slots. Antenn feed is locted t the center of the in wveguide. Ⅱ. Isolted Slot Chrcteriztion In order to use the design procedure [3], it is i- Mnuscript received Februry 1, 11 ; revised My 16, 11. (ID No J) 1 Deprtent of Electricl Engineering, Kore Advnced Institute of Science nd Technology (KAIST), Dejeon, Kore. Deprtent of Infortion & Counictions Engineering, Kore Advnced Institute of Science nd Technology (KAIST), Dejeon, Kore. Corresponding Author : Yun-Tek I (e-il : iyuntek@kist.c.kr) 97

2 JOURNAL OF THE KOREAN INSTITUTE OF ELECTROMANETIC ENINEERIN AND SCIENCE, VOL. 11, NO., JUN. 11 portnt to generte isolted slot dittnce s function of slot length nd the resonnt length of the slot s function of its offset. For feed slots, the resonnt length of the slot s function of its tilt ngle is lso required forthe design of the rry. A coercilly vilble EM siultion tool, HFSS, hs been used to generte the bsic slot dt subsequently used in the rry design. In the HFSS siultions for the shunt slot, the round ended.5 wide slot ws creted in 1 thick brodwll nd dittnce ws recorded t distnce of one-hlf the guide wvelength fro the center of the slot; the wveguide ws terinted in short circuit plced t qurter-wve distnce fro the center of the slot. Slot length ws vried nd t ech step of norlized coplex dittnce, conductnce (/ r ) nd susceptnce (B/ r), ws recorded nd ws norlized with resonnt conductnceof the slot. The design curve thus generted is shown in Fig. 1. The rel nd iginry prts of the dittnce re denoted s h 1(y) nd h (y), respectively, where y is the slot length norlized by the resonnt length, l/l r, which cn be written s (, ) Y x l ( ) h ( y) + jh ( y) g( x) 1 The wveguide width nd height re 1.5 nd 5, respectively. Next, the slot offset is chnged nd t ech step, the slot resonnt length is clculted where the iginry coponent of the dittnce ws zero. The resulting resonnt length of the slot s function of offset is shown in Fig.. We will denote the curve shown in Fig. s v(x), where x is the offset of the slot fro the center-line of the wveguide. Norlized resonnt conductnce, g ( x) r, of the isolted shunt slot s function of offset is plotted Fig.. Resonnt length of the brodwll slot versus offset. in Fig. 3. The curve g(x) cn be pproxited s follows [7], æ p x g ( x) K sin ç è ø b æ pb1 k K.9 cos ç b1 k è ø, (1) where nd b re the wveguide width nd height respectively, nd b 1 is the propgtion constnt of TE 1 ode nd k p l. The coupling slot ws lso chrcterized in HFSS for its resonnt resistnce s function of the tilt ngle. In the siultion odel, wveguide ws terinted t thedistnce of the hlf-guided wvelength fro the center of the slot nd resistnce ws recorded t the port locted t thedistnce of the hlf-guided wvelength fro Fig. 1. Norlized dittnce of isolted shunt slot versus slot length. Fig. 3. Norlized conductnce of isolted shunt slot s function of offset. 98

3 BHATTI et l. : DESIN OF A PLANAR SLOTTED WAVEUIDE ARRAY ANTENNA FOR X-BAND RADAR APPLICATIONS ( b / )( )( / l ) 3 K j k k b g 3 1 rs kl ò -kl 1 ù ê é ú ë 4lrs / l û æ z' ì 1 ée cos ç 4l / í ê è l ø î4l / l ë kr1 klrs ò -klrs - jkr1 - jkr æ z' rs e cos ç dz' 4lrs / è l ø kr rs e + k R ïü ýdz' ïþ - jkr where R is the distnce fro the point P (,, z ) esured in locl coordintes t the center of the th slot to the point Prs (,, z rs ) esured in locl coordintes t the center of the rs th slot. l nd l rs represent the slot length of th nd rs th, respectively., ù ú û Fig. 4. Resonnt length of the series coupling slot s function of tilt ngle. the center of the slot. At ech tilt ngle, the slot length ws vried to ke the iginry coponent of the slot ipednce equl to zero. The resulting curve is shown in Fig. 4. Ⅲ. Plnr Arry Design Procedure The ntenn design rests on the following design eqution []. Y where, K nd, f 1 K f 1 ( ) V V s 1 ( k k ) 1 j l h ( b / k)( k)( kb) ( ) cos( 1 ) ( p kl ) - ( b k ) p kl b l æ p x -K sin ç. è ø 1 () é R x x z z ë ( pq ) ( pq ) æz z ù ç ú è øû pq - + ê k k R is the distnce fro P to the left end of the slot Prs (,, - lrs ) nd R 1 is the distnce fro P to the right end of the slot, Prs (,, l rs ) nd is given s, é ( ) ( ) z ù R1 x - xpq + z z æ pq l ê - + ç - k pq ë è ú øû é ( ) ( ) z ù R x - xpq + z z æ pq l ê - + ç + k pq ë è ú øû The typicl configurtion of the two slots in n rry is given in Fig. 5. In (3), MC is the utul coupling ter for the th slot, which incorportes interctions fro ll of the slots in the rry. The perture distribution hs been clculted by spling the continuous perture t slot loctions for the 5 db first sidelobe level. The plnr rry is depicted in Fig. 6. It consists of twelve brnch wveguide with feed wveguide plced Zpq In eqution (), V is the ode voltge in the th s brnch wveguide nd V is the slot voltge of the th slot. Y is the ctive dittnce of the th slot. Y f ( x l ) ( ) f x, l, Y x l (, ) + MC (3) x ξ l ς R R R 1 l pq x w Wveguide center line V MC K g x l x l R S s rs 3å å s rs rs rs r 1 s 1 V rs ¹ (,,, ) Z Fig. 5. Two slots in plnr rry. 99

JOURNAL OF THE KOREAN INSTITUTE OF ELECTROMANETIC ENINEERIN AND SCIENCE, VOL. 11, NO., JUN. 11 Fig. 7. Aperture distribution for the plnr rry with truncted corner eleents. Fig. 6.

For the th slot in the rry, the distnce fro the origin is clculted s [9], ( -1) ( -1) ææ dz æ n dx r ç + ç ç è ø è ø è ø, where dx nd dz re the inter-eleent spcing long x nd z directions.

4 JOURNAL OF THE KOREAN INSTITUTE OF ELECTROMANETIC ENINEERIN AND SCIENCE, VOL. 11, NO., JUN. 11 Fig. 7. Aperture distribution for the plnr rry with truncted corner eleents. Fig. 6. Plnr slotted wveguide rry ntenn. behind. For the th slot in the rry, the distnce fro the origin is clculted s [9], ( -1) ( -1) ææ dz æ n dx r ç + ç ç è ø è ø è ø, where dx nd dz re the inter-eleent spcing long x nd z directions. The perture distribution is then clculted s follows [9], where A g p ( ), (4) p pr S J g( p) å p S n -1 n J ( p ) ( p ) n -1 Õ 1- n 1 un J( p ) è n -1 æ Õ 1- n 1 è un ¹> n n æ ç ø ç ø re zeros of ( ), S 1, where J1 p u. The clculted perture distribution is depicted in Fig. 7. A 3-D rry fctor plot corresponding to the spled perture distribution is shown in Fig. 8. Fig. 8. Arry fctor corresponding to the clculted perture distribution. After clculting the rry weights, the following procedure is used to clculte the slot diensions (offsets nd lengths). A set of initil offsets nd lengths is ssued for the rditing slots. Resonnt lengths nd zero offset re resonble choice for strting the design. These offsets nd lengths re used to clculte the following utul coupling terin eqution (3), V MC K g x l x l R S s rs 3å å s rs rs rs r 1 s 1 V rs¹ (,,, ) for every in the rry. Aserch is then conducted to find the couplet ( x, l, l ) tht stisfies the following reltion, 1

5 BHATTI et l. : DESIN OF A PLANAR SLOTTED WAVEUIDE ARRAY ANTENNA FOR X-BAND RADAR APPLICATIONS é ù ê f ( x, l ) ú I ê ú - I ê Y ( x, l ) ú êë ú û [ MC ] where Y/ is clculted fro the design curves, s (, l ) Y x ( h1 ( y ) h ( y )) g ( x ) +. Once this is stisfied, then ctive dittnce of the slot becoe spure rel. During this serch process, continuu of couplets tht stisfy this reltion is found. Siilrly, for the pq th slot, the se serch is conducted nd the continuu of couplets tht ke the ctive dittnce pure rel is found. But for given cceptble couplet for the th slot, there will only be one couplet for the pq th slot tht will stisfy the following eqution, Y pq s f (, ) pq xpq lpq VpqV s (, ) p. Y f x l V V This procedure provides set of cceptble couplets for ech slot. However, which couplet to choose will depend on the required dittnce level in ech brnchline. The finl cceptble couplets in brnch-line should stisfy the reltionship, Y N ( ) å C, n 1 where C is the required dittnce level in the th brnch wveguide. The entire procedure needs to be iterted s the new slot dt will give n iproved utul coupling clcultion nd the solution will converge fter 3 or 4 itertions. After clculting the rditing shunt slot dt, the series feed slot dt is then clculted ccording to the procedure reported in [9]. The su of the series of slot resistnces is given by, M å r W, 1 nd 1, M, r is the norlized resonnt resistnce of the th slot, B is the slot excittion function, K is the excittion norliztion constnt, nd W1 for the end-feed or W for the center feed. B is given in ters of the perture distribution. where r KB ( ), (5) (6) (7) (8) N ( ) (, ) B å A n, n 1 where N is the nuber of shunt slots fed by the th series slot. Using these resistnce vlues, the corresponding slot ngles re clculted using the design curves or the following reltionship, (9) R b1 l é l g ù.131 êiq sinq + Jq cosq ú R k b ë û, (1) where thet is the tilt ngle of the series slot, nd æ p æ p cos K1 cos K I ç ç q è ø ± è ø J 1- K 1- K q 1 K1 b1 l cosq ± sinq. K k Once slot resistnce s function of the slot tilt ngle is known, we cn clculte the slot length for different slot ngles fro the design curve shown in Fig. 4. The pplied slot length (l) is 16.5 nd the offset lengths (x) re.1, 1.85, 1.6, 1.,.8, nd.7 fter the clcultion nd CST-siultion. The feed wveguide is fed t the center through stndrd X-bnd wveguide. The width of the feed slot is optiized in CST to get the desired tch t Hz. A 3-D exploded odel of the ntenn ssebly is shown in Fig. 9. Fig. 9. Exploded view of ntenn ssebly. 11

JOURNAL OF THE KOREAN INSTITUTE OF ELECTROMANETIC ENINEERIN AND SCIENCE, VOL. 11, NO., JUN. 11 Fig. 1. Surfce currents on the perture. Fig. 1. Coprison of the esured nd siulted E-plne ptterns. Fig. 11. Siulted 3-D pttern of the ntenn.

It cn be observed tht the ount of current on the slots decreses with incresing distnce fro the center of the ntenn, tht exhibits plitude tpering. A siulted 3-D pttern of the ntenn is depicted in Fig.

6 JOURNAL OF THE KOREAN INSTITUTE OF ELECTROMANETIC ENINEERIN AND SCIENCE, VOL. 11, NO., JUN. 11 Fig. 1. Surfce currents on the perture. Fig. 1. Coprison of the esured nd siulted E-plne ptterns. Fig. 11. Siulted 3-D pttern of the ntenn. The surfce currents on the plne contining the rditing slots re depicted in Fig. 1. It cn be observed tht the ount of current on the slots decreses with incresing distnce fro the center of the ntenn, tht exhibits plitude tpering. A siulted 3-D pttern of the ntenn is depicted in Fig. 11. A coprison of the esured nd siulted ptterns is given in Fig. 1. The first sidelobe level of the ntenn is 5.6 db down nd the 3-dB bewidth of the ntenn is 8. degrees. The esured gin of the ntenn is 6 dbi. A coprison of the esured nd siulted reflection coefficients of the ntenn is given in Fig. 13. The ntenn shows bndwidth of MHz for the 1 db input reflection coefficient. The rdition efficiency is clculted s, in l Efficiency, Are 4p nd efficiency of the ntenn is 46 %. (11) Fig. 13. Coprison of the esured nd siulted input reflection coefficients. Ⅳ. Conclusions A plnr slotted wveguide ntenn hs been designed t 9.37 Hz using brodwll rditing slots. The ntenn design is bsed on the coonly used Elliot s slotted wveguide ntenn design procedure, using the coercilly vilble EM siultion tools, HFSS & CST MWS. The ntenn hs been designed for 5 db sidelobe level nd bewidth of 8.. Coprisons of the esured nd siulted fr-field ptterns nd input reflection coefficients hve been reported, nd show xiu 1 db error within the esuredbndwidthdue to loss or lekge in thewveguide dpter. 1

Advnceent of Technology (KIAT) through the Hun Resource Trining Project for Regionl Innovtion. References [1] Phillip N. Richrdson, H. Y.

7 BHATTI et l. : DESIN OF A PLANAR SLOTTED WAVEUIDE ARRAY ANTENNA FOR X-BAND RADAR APPLICATIONS This reserch ws finncilly supported by the Ministry of Eduction, Science Technology (MEST) nd Kore Institute for Advnceent of Technology (KIAT) through the Hun Resource Trining Project for Regionl Innovtion. References [1] Phillip N. Richrdson, H. Y. Lee, "Design nd nlysis of slotted wveguide rrys," Microwve Journl, pp , Jun [] Robert S. Elliot, L. A. Kurtz, "The design of sll slot rrys," IEEE Trns. Antenns Propgtion, vol. AP-6, pp , Mr [3] Robert S. Elliot, "An iproved design procedure for sll rrys of shunt slots," IEEE Trns. Antenns Propgtion, vol. Ap-31, pp , Jn [4] Robert S. Elliot, W. R. O Loughlin, "The design of slot rrys including internl utul coupling," IEEE Trns. Antenns Propgtion. vol. Ap-34, pp , Sep [5] H. Y. Yee, "The design of lrge wveguide rrys of shunt slots," IEEE Trns. Antenns Propgtion, vol. 4, no. 7, pp , Jul [6] Aln J. Sngster, A. H. I. McCroick, "Theoreticl design nd synthesis of slotted wveguide rrys," IEE Proc. H. Microwves, Antenn nd Propgtion, vol. 136, no. 1, Feb [7] eorge J. Stern, R. S. Elliot, "Resonnt length of longitudinl slots nd vlidity of circuit representtion: theory nd experients," IEEE Trns. Antenns Propgtion, vol. Ap-33, no. 11, pp , Nov [8] Lrs. Josefsson, "Anlysis of longitudinl slots in rectngulr wveguides," IEEE Trns. Antenns Propgtion, vol. AP-33, pp , Dec [9] Robert S. Elliot, Antenn Theory nd Design, No. 6, Prentice Hll, Inc, Rshid Ahd Bhtti ws born in Bhwl-Ngr, Pkistn, on July 14, He received the B.Sc. degree in electricl engineering fro University of Engineering nd Technology, Txil, in 1999 nd the M.Sc. degree in electricl engineering fro Ntionl University of sciences nd Technology (NUST), Rwlpindi, Pkistn, in August, 5. Currentlyhe is working towrd the Ph.D. degree in electricl engineering t the Kore Advnced Institute of Science nd Technology (KAIST), Dejeon, Kore. Fro Septeber 1999 to Deceber 5, he worked s n RF nd Antenn Reserch Engineer t Advnced Engineering Reserch Orgniztion (AERO), Pkistn. Here, he hs been involved in the EMI/EMC testing nd design of slotted wveguide rry ntenns for trckingrdrs. His current reserch interests include the design of MI- MO ntennrrys, ultibnd ntenns for portble couniction devices, slotted wveguidentenns nd nuericl ethods in electrognetics. Byeong-Yong Prk ws born in Dejeon, Kore. He received the B.S. degree in division of electricl engineering fro ChungN Ntionl University, Kore, in 8, the M.S. degree in electricl engineering fro Kore Advnced Institute of Science nd Technology (KAIST), Dejeon, Kore, in 1, nd is currently working towrd the Ph.D. degree in electricl engineering tkore Advnced Institute of Science nd Technology (KAIST), Dejeon, Kore. His current reserch interest is the design of MIMO ntenn rrys for portble couniction devices. 13

JOURNAL OF THE KOREAN INSTITUTE OF ELECTROMANETIC ENINEERIN AND SCIENCE, VOL. 11, NO., JUN. 11 Yun-Tek I ws born in ChungN, Kore, on June 7th, 1978. He received the B.S. degreein division of electricl engineering nd coputer science fro Hnyng University, Kore, in 5, the M.

degree in electricl engineering t the Kore Advnced Institute of Science nd Technology (KAIST), Dejeon, Kore. He ws engged in developent of RFID ntenns nd illieter-wve be-foring systes fro 5 to 7.

8 JOURNAL OF THE KOREAN INSTITUTE OF ELECTROMANETIC ENINEERIN AND SCIENCE, VOL. 11, NO., JUN. 11 Yun-Tek I ws born in ChungN, Kore, on June 7th, He received the B.S. degreein division of electricl engineering nd coputer science fro Hnyng University, Kore, in 5, the M.S. degree in electronic nd electricl engineering fro the Pohng University Science nd Technology t Pohng (POSTECH), in 7, nd is currently workingtowrd the Ph.D. degree in electricl engineering t the Kore Advnced Institute of Science nd Technology (KAIST), Dejeon, Kore. He ws engged in developent of RFID ntenns nd illieter-wve be-foring systes fro 5 to 7. His current reserch interests re MIMO ntenn systes nd rdr systes including ntenn design. Seong-Ook Prk (M 5) ws born in KyungPook, Kore, in Deceber He received the B.S. degree fro KyungPook Ntionl university, in 1987, the M.S. degree fro Kore Advnced Institute of Science nd Technology, Seoul, in 1989, nd the Ph.D. degree fro Arizon Stte University, Tepe, in 1997, ll in electricl engineering. Fro Mrch 1989 to August 1993, he ws Reserch Engineer with Kore Teleco, Dejeon, working with icrowve systes nd networks. He lter joined the Telecouniction Reserch Center, Arizon Stte University, until Septeber Since October 1997, he hs been with the Infortion nd Counictions University, Dejeon, first s n Associte Professor, nd currently s Professor t the Kore Advnced Institute of Science nd Technology, IT convergence Cpus. His reserch interests include obile hndset ntenn, nd nlyticl nd nuericl techniques in the re of electrognetics. Dr. Prk is eber of Phi Kpp Phi. 14

Two-layer slotted-waveguide antenna array with broad reflection/gain bandwidth at millimetre-wave frequencies

Two-layer slotted-waveguide antenna array with broad reflection/gain bandwidth at millimetre-wave frequencies Two-lyer slotted-wveguide ntenn rry with rod reflection/gin ndwidth t millimetre-wve frequencies S.-S. Oh, J.-W. Lee, M.-S. Song nd Y.-S. Kim Astrct: A 24 24 slotted-wveguide rry ntenn is presented in