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1 Chalmrs Publication Library Ovrviw of dvlopmnts of th lvn Fds This documnt has bn downloadd from Chalmrs Publication Library (CPL). It is th author s vrsion of a work that was accptd for publication in: th Europan Confrnc on Antnnas and Propagation, EuCAP, Gothnburg, Swdn, - April Citation for th publishd papr: Yang, J. ; Kildal, P. ; Pantalv, M. () "Ovrviw of dvlopmnts of th lvn Fds". th Europan Confrnc on Antnnas and Propagation, EuCAP, Gothnburg, Swdn, - April pp. -. Downloadd from: Notic: Changs introducd as a rsult of publishing procsss such as copy-diting and formatting may not b rflctd in this documnt. For a dfinitiv vrsion of this work, plas rfr to th publishd sourc. Plas not that accss to th publishd vrsion might rquir a subscription. Chalmrs Publication Library (CPL) offrs th possibility of rtriving rsarch publications producd at Chalmrs Univrsity of Tchnology. It covrs all typs of publications: articls, dissrtations, licntiat thss, mastrs thss, confrnc paprs, rports tc. Sinc it is th official tool for Chalmrs official publication statistics. To nsur that Chalmrs rsarch rsults ar dissminatd as widly as possibl, an Opn Accss Policy has bn adoptd. Th CPL srvic is administratd and maintaind by Chalmrs Library. (articl starts on nxt pag)

2 Ovrviw of Dvlopmnts of th Elvn Fds Jian Yang, Pr-Simon Kildal, Miroslav Pantalv, Dpt. of Signals and Systms, Chalmrs Univrsity of Tchnology, SE-9 Gothnburg, Swdn Onsala Spac Obsrvatory, Chalmrs Univrsity of Tchnology, S-9 Gothnburg, Swdn chalmrs.s Abstract An ovrviw of diffrnt vrsions of th Elvn fd and rcnt dvlopmnt is prsntd in th papr. Elvn fds hav a narly constant bamwidth and a fix phas cntr, with a prformanc of an aprtur fficincy highr than %, - db rflction cofficint, -.db radiation fficincy, and -db cross-polar lvl, ovr a dcad bandwidth. Th Elvn fd can b vry compact aftr applying nwly dvlopd optimization algorithms, and som nw rsults of th fd in dual-rflctor antnnas ar rportd hr. Indx Trms dcad-band fd, rflctor antnna, radio tlscop, VLBI, SKA I. INTRODUCTION Nxt gnration radio tlscops, with two wll-known xampls of SKA (Squar Kilomtr Array) and VLIBI (Vry Long Baslin Intrfromtry), rquirs ultra-widband systms. Svral nw fd tchnologis for such dcadbandwidth radio tlscops hav bn proposd, such as th Elvn fd, th quadrupl-ridgd flard horn [], th sinuous fd [] and th quasi slf-complmntary antnna []. Diffrnt vrsions of Elvn fds for diffrnt applications ovr diffrnt bands hav bn dvlopd during th rcnt yars [] [9], ranging from low frquncy such as MHz to high frquncy of GHz; s Fig.. Th nwly dvlopd opposition algorithms and th novl dsign approachs allow to dsign light wight, low profil dsign, with diffrnt altrnativs for fding and improvd aprtur fficincis. Th main advantags of th Elvn fd compard to th altrnativ dcad band fds mntiond abov ar th narly constant bamwidth and th fixd phas cntr location. Furthrmor, th Elvn fd is on of th most compact dcad-bandwidth fds for rflctors. W prsnt an ovrviw of th dvlopmnt of Elvn fds, rport nw rsults and discuss th futur dvlopmnt in th papr. II. APPLICATIONS Th main applications of th Elvn antnna is as a fd for rflctor antnnas in radio tlscops bcaus th Elvn fd can provid a narly constant bamwidth and a fix phas cntr location ovr a dcad bandwidth. W hav bn working on th GHz Elvn fd for th VLBI projct and GHz Elvn fd for th SKA projct. Th Elvn fd is also vry attractiv for low frquncy applications, du to its compact siz; s Sct. VI. Fig.. Diffrnt Elvn fds Th Elvn antnna can also b usd in othr applications, such as monopuls tracking [], dual-band Satcom fd [] and widband MIMO antnna []. III. PERFORMANCE IMPROVEMENT W prsnt th prformanc improvmnt of Elvn fds in this sction. A. Aprtur Efficincy It is noticd that all proposd UWB fds ar non-bor (Body of Rvolution) antnnas []. Thrfor, incrasing BOR fficincy [], [] is critical in ordr to hav a high aprtur fficincy for a UWB fd. Th BOR fficincy, thrfor th aprtur fficincy, of th Elvn fd has bn improvd by using th circular foldd dipols [9]. Fig. shows a comparison of th aprtur fficincy and its sub-fficincis btwn th straight Elvn fd [] and th circular Elvn fd [9]. It can b sn that thr is a significant improvmnt at both low and high frquncy nds.

3 9% Rflction Cofficint (db) % Efficincy % % sp % BOR % pol % ill % Masurd pol Masurd pol φ % ap 9 Frquncy (GHz) Frquncy (GHz) % Rflction Cofficint (db) 9% Efficincis % % φ % pol % sp 9 Simulatd Masurd % BOR % ap ill %. Frquncy (GHz). 9 Fig.. Improvmnt of aprtur fficincy which is calculatd basd on masurd radiation function with a subtndd angl of of straight and circular Elvn fd. Frquncy (GHz) 9 Fig.. Masurd rflction cofficints of straight and circular Elvn fds. B. Rflction Cofficint C. Radiation Efficincy Fig. shows th radiation fficincy which stats th ohmic loss of th straight and th circular Elvn fds. A -.db radiation fficincy corrsponds to a.k incras in nois tmpratur whn th fd is coold down to cryognic tmpraturs of K. Simulatd Rflction Cofficint (db) Obtaining a low rflction cofficint is always a focus in dsign of Elvn fds. Svral optimization mthods hav bn dvlopd, togthr with gntic algorithm (GA) [] []. Fig. shows th masurd rflction cofficints of th GHz straight Elvn fd [] and th circular Elvn fd [9], by using GA optimizd schm. W ar now dsigning a..ghz Elvn fd by using so-calld social civilization algorithm (SCA). Fig. shows th simulatd rflction cofficint of this fd, which is almost blow - db ovr th whol band. A prototyp of this fd is undr fabrication, and w bliv that th masurd rflction cofficint of th Elvn fd can achiv to th simulatd lvl.,,,,,,,9 Frquncy (GHz),,, Fig.. Simulatd rflction cofficint of a nw dsignd..ghz Elvn fd. D. Cross-polar Lvl Th cross-polar radiation pattrn has bn improvd from a lvl blow - db for th straight Elvn fd [] to a lvl blow - db for th circular Elvn fd [9], as shown in Fig..

4 Radiation Efficincy (db)... simulatd using CST masurd at Chalmrs. masurd at DTU Frquncy (GHz) 9 9% % Efficincy % Radiation Efficincy (db).. Simulatd φ % pol sp BOR % ill % ap. Masurd Frquncy (GHz) 9 Frquncy (GHz) 9 Fig.. Calculatd aprtur fficincy and its sub-fficincis basd on simulatd radiation function whn th circular fd illuminats a dual-rflctor antnna (including a sub-rflctor) with a subtndd angl of for th main rflctor. Radiation fficincy of th straight and th circular Elvn fds. IV. D UAL - REFLECTOR S YSTEM GHz.GHz.GHz GHz GHz GHz GHz GHz GHz GHz 9GHz GHz GHz GHz Both VLBI and SKA projcts ar using dual-rflctor antnnas. W hav studid th prformanc of th Elvn fd in a dual-rflctor antnna, as shown in Fig.. Th subtndd angl is and for th sub-rflctor and th main rflctor, rspctivly. Th rflction cofficint of th fd is almost not affctd by th sub-rflctor and th aprtur fficincy of th whol antnna is calculatd, as shown in Fig., which indicats a good prformanc. As rportd in [], Elvn fds provid an optimal prformanc whn th subtndd angl is from to for primary rflctor systms. By using a dual-rflctor arrangmnt, th Elvn fd can b usd in an optimal prformanc for diffrnt subtndd angls. W ar invstigating mor cass and will rport rsults in futur publications. Amplitud (db) % %. Fig.. % V. F EEDING M ECHANISM θ Fig.. Masurd radiation pattrns in plan of th circular Elvn fd. Rd solid lin co-polar; Blu dash lin cross-polar. Elvn fds ar multi-port antnnas, which provids flxibility for systm configuration. On th othr hand, multipl ports rquir multipl low nois amplifirs (LNAs) in radio tlscops. Fig. shows thr diffrnt fding mthods: port fding [], balun fding [9] [] and cntr connction fding. Fig. 9 shows th rflction cofficints for ths thr fding mthods. Furthr improvmnt on prformanc of ths thr fdings is undr going.

5 Fig.. Thr fding mthods: ) -port fding; ) -port balun fding; ) -port cntr connction fding. All port impdancs ar Ohms. Rflction Cofficint (db) Masurd pol Masurd pol Fig.. Siz rduction of Elvn fds, whr ϕ is th diamtr of a fd aprtur, H th hight and V th volum of a fd, and λ is th wavlngth of th lowst opration frquncy. It can b sn that th nw dvlopd fd (at right-down cornr) has a volum of lss than on fifth of th straight Elvn fd (at lft-up cornr), a significant siz rduction. VI. S IZE C OMPACTNESS Frquncy (GHz) 9 Masurd Rflction Cofficint (db) Simulatd VII. M ECHANICAL D ESIGN Frquncy (GHz) 9 Rflction Cofficint (db) Simulatd Pol A Simulatd Pol B Fig. 9. Siz compactnss of a fd is important, spcially in th cas whr th fd should b insid a cryostat or in lowfrquncy cass whr th fd can b vry big and havy. Fig. summarizs th dvlopmnt of th fd siz rduction. From th figur, th nwst Elvn fd can hav a siz smallr than on fifth of that of th fd prsntd in [] Frquncy (GHz).. Rflction cofficint of Elvn fds of th thr fding mthods. Th oprational band of th Elvn fd, th particular application and th fding ntwork ar stting up diffrnt challngs on th mchanical dsign. Paramtric studis show that rlativly thick dipols (thicknss of up to mm) can b usd for th frquncy bands up to about GHz. This implis using low prmittivity foam matrial (lik th Rohacll foam) for dipol support and avoiding microwav substrats having th drawback of high tangnt dlta and prmityvity cofficints. For frquncis highr than GHz, th thicknss of th dipols should b dcrasd to maintain low rflction cofficint which rquirs th mchanical dsign to us microwav substrat for th dipols. Th particular application, spcially th cryognic intgration of th fd ntails using of a substrat with wll-matchd cofficints of thrmal xpansion of th dilctric to th on of th coppr. Furthrmor th coppr mtallisation should b thick nough to hav good thrmal conductivity and allow cooling of th ptal to tmpratur of about K. Th fding ntwork is on of th most challnging tasks in mchanical dsign. Th Elvn fd with -port fding has rlativly simpl mchanical dsign, but th us of twin-lad lins sts vry high rquirmnts on th manufacturing and assmbly tolrancs. Th cntral fding has mor complicatd mchanical dsign

6 but uss standard coaxial cabls. Dtails on th mchanical dsign ar publishd in [] and []. TABLE I SUMMARY OF ELEVEN FEED PERFORMANCE Exampls Aprtur Efficincy > % ovr. GHz Rflction cofficint < - db ovr GHz (masurd) < - db ovr.. GHz (simulatd) Radiation Efficincy -. db ovr GHz Cross-polar Lvl < - db ovr. GHz.λ.λ (with mtal outr wall), Siz.λ.λ (with dilctric outr wall), (Diamtr Hight) (λ is th wavlngth of th lowst oprating frquncy) coaxial ports for dual polarization, Fding Mthods Balun fding ( or coaxial ports for dual polarization), cntr connction fding ( coaxial ports for dual polarization) VIII. CONCLUSIONS Tabl I summarizs th ovrall prformanc of Elvn fds. Th Elvn fd can b usd in both primary rflctor antnnas and dual-rflctor antnnas, whr in th formr cas th optimal subtndd angl is in th arrang of and in th lattr cas th optimal subtndd angl for th main rflctor may b adjustd by using diffrnt sub-rflctors. Th siz of Elvn fds is vry compact. Furthr dvlopmnts on fding structurs, bttr rflction cofficint, and dualrflctor antnna systms ar undr going. REFERENCES [] A. Akgiray, S. Winrb, and W. Imbrial, Dsign and masurmnts of dual-polarizd widband constant-bamwidth quadrupl-ridgd flard horn, in IEEE AP-S Intrnational Symp. on Antnnas Propag. Spokan, Washington: IEEE, - July, pp.. [] R. Gawand and R. Bradly, Towards an ultra widband low nois activ sinuous fd for nxt gnration radio tlscops, IEEE Trans. Antnnas Propag., no. 99, pp. 9 9, Jun. [] G. Corts-Mdllin, Non-planar quasi-slf-complmntary ultrawidband fd antnna, IEEE Trans. Antnnas Propagat., vol. 9, no., pp. 9 9, Jun. [] R. Olsson, P. Kildal, and M. Shilds, Masurmnts of a to MHz low loss Elvn fd for th m radio tlscop at Grn Bank, in IEEE Antnnas and Propagation Socity Intrnational Symposium. IEEE,, pp.. [] Y. B. Karandikar and P.-S. Kildal, Optimization of -MHz Elvn Fd for GMRT, in Th Scond Europan Confrnc on Antnnas and Propagation,. EuCAP. [] J. Yang and P. Kildal, Improvmnt of input rflction cofficint of lvn antnna a compact widband fd for rflctor antnnas, in Intrnational Symposium on Antnnas and Propagation, Niigata, JAPAN, - August,. [] J. Yang, M. Pantalv, P. Kildal, B. Klin, Y. Karandikar, L. Hlldnr, N. Wadfalk, and C. Baudoin, Cryognic GHz Elvn fd for rflctor antnnas in futur widband radio tlscops, IEEE Transactions on Antnnas and Propagation, vol. 9, no., pp. 9 9,. [] J. Yang, M. Pantalv, P. Kildal, and L. Hlldnr, Dsign of compact dual-polarizd. GHz Elvn fd for dcad bandwidth radio tlscops, IEEE Transactions on Antnnas and Propagation, vol., no., pp.,. [9] J. Yin, J. Yang, M. Pantalv, and L. Hlldnr, Th circular Elvn antnna: A nw dcad-bandwidth fd for rflctor antnnas with high aprtur fficincy, appar in IEEE Transactions on Antnnas and Propagation, vol.,. [] J. Yin, J. A. Aas, J. Yang, and P.-S. Kildal, Monopuls tracking prformanc of multi-port Elvn antnna for us in trminals for satllit communications. Th nd Eur. Confrnc on Antnnas and Propagation (EuCAP ), Edinburgh, - Novmbr. [] A. Yasin, J. Yang, and T. Ostling, A compact dual-band fd for rflctor antnnas basd on chok horn and circular Elvn antnna, IEEE Transactions on Antnnas and Propagation, vol., no., pp., 9. [] X. Chn, P. Kildal, J. Carlsson, and J. Yang, Comparison of rgodic capacitis from widband MIMO antnna masurmnts in rvrbration chambr and anchoic chambr, IEEE Antnnas and Wirlss Propagation Lttrs, vol., pp. 9,. [] P. Kildal and Z. Sipus, Classification of rotationally symmtric antnnas as typs bor and bor, IEEE Antnnas Propag. Mag, vol., no., p., 99. [] P. Kildal, Factorization of th fd fficincy of paraboloids and cassgrain antnnas, IEEE Transactions on Antnnas and Propagation, vol., no., pp. 9 9, 9. [] J. Yang, S. Pivnnko, and P. Kildal, Comparison of two dcadbandwidth fds for rflctor antnnas: th lvn antnna and quadridg horn, in Antnnas and Propagation (EuCAP), Procdings of th Fourth Europan Confrnc on. IEEE,, pp.. [] J. Yang, X. Chn, N. Wadfalk, and P.-S. Kildal, Dsign and ralization of a linarly polarizd Elvn fd for - GHz, IEEE Antnnas Wirlss Propag. Ltt., vol., pp., 9. [] J. Yang and P. Kildal, Optimization of rflction cofficint of larg logpriodic array by computing only a small part of it, IEEE Transactions on Antnnas and Propagation, vol. 9, no., pp. 9 9,. [] J. Yang, Priodicity of th input impdanc of log-priodic array antnnas, IET Microwavs, Antnnas & Propagation, vol., no., pp.,. [9] A. Zamanifkri and J. Yang, Two octavs bandwidth passiv balun for th Elvn fd for rflctor antnnas, in IEEE Antnnas and Propagation Socity Intrnational Symposium (APSURSI). IEEE,, pp.. [] H. Raza, J. Yang, and A. Hussain, Masurmnt of radiation fficincy of multiport antnnas with fding ntwork corrctions, IEEE Antnnas and Wirlss Propagation Lttrs, vol., pp. 9 9,. [] R. Raza, J. Yang, and M. Pantalv, Intgration of UWB planar baluns into th Elvn fd, IET Microwavs, Antnnas & Propagation, submittd,.