Effect of Warm Ionized Plasma Medium on Radiation Properties of Mismatched Microstrip Termination

Transcription

1 J. Elctrmagntic Analysis & Alicatins, 9, 3: di:1.436/jmaa Publishd Onlin Stmbr 9 ( 181 Effct f Warm Inizd Plasma Mdium n adiatin Prrtis f Mismatchd Micrstri Trminatin Ayman Al-SAWALHA Physics Dartmnt, Cllg f Scinc, King Faisal Univrsity, Saudi Arabia. drswalha@htmail.cm civd Aril 14 th, 9; rvisd July 13 th, 9; acctd August nd, 9. ABSTACT Study f radiatin rrtis f mismatchd micrstri trminatin is carrid ut in warm inizd lctrn lasma mdium. Linarisd hydrdynamic thry culd with vctr wav tchniqu is usd t invstigat radiatin attrns and radiatd wr f a micrstri mismatchd trminatin in n cmnnt lctrn lasma mdia fr diffrnt lasma t surc frquncis.ths rrtis ar usd t cmar th rfrmanc f an n circuit discntinuity with ths f matchd micrstri trminatin. Matchd trminatins ar fund mr suitabl fr alicatins at highr frquncis than an n circuit discntinuity in th lasma mdium thugh in fr sac thy ar lss suitabl. Kywrds: Mismatchd Trminatin, On Circuit Discntinuity, Matchd Micrstri Trminatin, Inizd Plasma 1. Intrductin Micrstri antnna has rvn t b an ffctiv, light wight and quit inxnsiv radiatr fr arsac vhicls [1]. Many wrkrs hav rrtd radiatin rrtis f diffrnt micrstri radiatrs in fr sac [ 4]. Mtallic and dilctric lsss, brakdwn ffct at highr wr lvl and radiatins frm discntinuitis, hwvr, limits th alicatin f a micrstri lin structur vr th grund lan [5]. adiatins frm micrstri discntinuity bcm quit dminant at micrwav frquncis and hnc bcm majr limiting factr. Hnc, it is always ncssary t cntrl thm smhw. adiatins frm an n circuit micrstri discntinuitis ar invstigatd rcntly [6] in an inizd lasma mdium f infinit thicknss. adiatins frm a mismatchd trminatin in an inizd lasma mdium ar invstigatd in this cmmunicatin. Using ths rlatins, rfrmanc f tw thr tys f discntinuitis viz. a matchd micrstri trminatin and an n circuit micrstri trminatin ar invstigatd in fr sac as wll as in inizd ht lasma mdium. In stri lin structur, fild ds nt li unifrmly in btwn th cnducting atch and th grund lan but sm fring filds lak in th air nar th dgs f th stri. Dilctric larizatin bnath th stri taks lac which givs ris t th larizatin currnt in additin t th alrady xisting stri currnt [5]. Cnsidring bth ths currnts tgthr, radiatin attrns and radiatd wr by a mismatchd trminatin ar btaind fr diffrnt lasma t surc frquncy ( P ). With th rsnc f an actual inizd lasma mdium, ffctiv rmittivity f structur changs marginally in cmarisn t th ffctiv rmittivity in fr sac and hnc rsnanc frquncy als changs marginally [7]. It is fund that rcnt dviatin in frquncy is abut.3% in th rsnc f an inizd lasma mdia f infinit thicknss which ds nt affcts rdictd rsults sriusly.. adiatin Fild Exrssins Th gmtry and crdinat systm f a mismatchd micrstri trminatin is shwn in Figur 1. A stri lin abv th grund lan is lcatd alng th z-axis f th crdinat systm. Th thicknss f th dilctric substrat is cnsidrd t b " h", width f stri " w",rlativ rmability and rmittivity r 1 and r 1 rsctivly. It is cnsidrd hr that th trminatin mismatchs th stri. Far filds ar btaind by cnsidring a magntic currnt dnsity aln with a rfct lctric currnt cnditin. Fr stri lin cnfiguratin, th intgratin t find lctric fild using vctr tntial is carrid ut vr a crss Cyright 9 Scis

2 18 Effct f Warm Inizd Plasma Mdium n adiatin Prrtis f Mismatchd Micrstri Trminatin sctin which givs a cmbinatin f currnts frmd by larizatin currnt ( alng x-axis) and a stri currnt (alng z-axis). Lt th stri currnt b whr jkz jkz I I ( ) s k j ff (1) is th wavlngth in fr sac, ff is th ffctiv dilctric cnstant f substrat matrial, is th rflctin cfficint at th nd f th lin and its limiting valu lis in btwn and 1, and is th has angl btwn th incidnt wav and th rflctd wav. Assuming currnt amlitud is t b cnstant a crss th stri lin, th surfac currnt dnsity in z-dirctin fr nd fd lin will bcm jt J I iˆ () s s z Th larizatin currnt dnsity in x-dirctin will b 1 I s jt J ˆ h i x (3) z whr i ˆx and i ˆz ar unit vctrs in th x and z dirctin rsctivly and is th actual dilctric cnstant f th substrat matrial. Cnsidring th rsnc f bth ths currnts tgthr and fllwing th mthd f [8], th xrssins fr th radiatin attrns ar btaind in lctrmagntic md as wll as in lctracustic md. Ths xrssins ar:.1 In Elctrmagntic Md j6hwi j( tr) E r A ( cs ) ( A )cs ( A cs ) cs ( A ) cs A ( cs ) ( A cs ) j6hwio j( tr) E r Acs Acs sin ( Acs ) ( Acs ) (4) (5) Figur 1. Th gmtry and crdinat systm f a mismatchd micrstri trminatin whr: w sin( sinsin ) w ( sinsin ) A A 1 w j( sin sin ) is th ragatin cnstant in lctrmagntic md. is th ragatin cnstant in fr sac (radian/m) is th angular lasma frquncy ( sc 1 ) is th angular surc frquncy ( sc 1 ). In Elctracustic Md E whi r( ) (cs sincs ) k ( k cs ) k ( k cs ) whr j( tr) (sin cs cs ) w sin( sinsin ) w ( sinsin ) c A w j( sin sin ) (6) Cyright 9 Scis

3 Effct f Warm Inizd Plasma Mdium n adiatin Prrtis f Mismatchd Micrstri Trminatin Figur. E radiatin attrns fr A 1. and. Pwr in db 3 33 A=1. A=. A,.7, Pwr in db A= A= Figur 3. E radiatin attrns fr A 1. and A.,.7, A : is th ragatin cnstant in lasma md. Ths valu f E, E and E ar cmutd and lttd in Figurs ( 4) fr tw diffrnt valus f lasma t surc frquncy. Cmutatins ar carrid ut fr h.158cm, w.471 cm,.31, 3., ratin frquncy = 1.GHz,.7 and. E Pattrns in fr sac ( A 1.) ar almst unifrm. adiatin intnsity in th nd fir dirctin ( ) is slightly mr than th radiatin intnsity in th bradsid dirctin ( 9 ). On incrasing lasma t surc frquncy ( A.), radiatin attrn mdifis drastically and dirctin f maximum intnsity shifts Cyright 9 Scis

4 184 Effct f Warm Inizd Plasma Mdium n adiatin Prrtis f Mismatchd Micrstri Trminatin 4 3 E in db Thta in dgr Figur 4. E radiatin attrn in lasma fr A.,.7, Tabl 1. bamwidth in and lans fr A 1. and A. E E Frnt dirctin Fr Sac ( A 1.) dirctin Frnt dirctin Plasma ( A.) dirctin Frnt dirctin Fr Sac ( A 1.) dirctin Frnt dirctin Plasma ( A.) dirctin frm ( ) t ( 18 ) dirctin and minimum aars at ( ). Almst similar bhavirs aar fr E attrns. Ths attrns in th fr sac ( A 1.) ar almst symmtric in all th fur quadrants, but fr highr lasma t surc frquncy valu ( A.), th bam width in than in ( ) ( 18 ) dirctin. dirctin is much smallr E radiatin attrns indicat that nly n lb a ars in th 5 t 6 rang. On substituting 1. and all th xrssins btaind fr mismatchd micrstri trminatin rduc immdiatly t ths f n circuit micrstri discntinuity [6]. Similarly n substituting and, xrssins fr micrstri matchd trminatin can b btaind [8]. 3. adiatd Pwr Th wr radiatd by th micrstri mismatchd trminatin thrugh ur half sac is btaind by using Pynting vctr. Fr diffrnt valus f lasma t surc frquncis, xrssins fr radiatd wr ar btaind by using th mthd f [8].Ths xrssins ar: 3.1 Fr Elctrmagntic Md 15hw AI P S1 cs S cs sindd whr A ( cs ) ( A )cs ( A cs ) S1 ( A ) cs A ( cs ) ( A cs ) And S Acs Acs ( Acs ) ( A cs) and th radiatin rsistanc in lctrmagntic md can b dfind as P I (7) (8) Cyright 9 Scis

5 Effct f Warm Inizd Plasma Mdium n adiatin Prrtis f Mismatchd Micrstri Trminatin Fr Elctracustic Md P mh I (cs sincs ) k / 4 / [ 8 n( ) / / (sincs cs ) ] sin ( k cs ) ( k cs ) k X dd and th radiatin rsistanc in lasma md dfind as P I (9) can b...(1) Ths valus f and ar cmutd and ltt fr diffrnt valus f lasma t surc frquncis in Figur 5.In th lctrmagntic md, wr radiatd in fr sac ( A 1. ) is maximum but dcrass n incrasing lasma t surc frquncy. On th thr hand, lasma md fild attrns giv a quasi ridic attrn. Initially, radiatd wr in lasma md is lss than th radiatd wr in lctrmagntic md but it vr taks in btwn th rang A t.5. During th vyag in fr sac, arsac vhicl intracts with lasma mdia and radiats lctracustic wavs in additin t th usual lctrmagntic wavs. Prsnc f th lctracustic wav is mainly rsnsibl fr such variatin in this lasma mdia. It is vidnt frm th xrssins f radiatd wr that thy ar a functin f rflctin cfficint. Th variatins f radiatd wr in fr sac A 1.r ( ) and in lasma mdia ( 1) ar rsntd fr bth lctrmagntic md and lngitudinal lasma md in Figur 6. In fr sac A 1.,radiatd wr in lctrmagntic md is maximum fr (matchd trminatin).as mismatch incrass, radiatd wr dcrass and bcms minimum at.8.thraftr it bcms almst unifrm u t 1. (n circuit micrstri trminatin).on incrasing th lasma t surc frquncy A., th radiatd wr by a matchd trminatin bcms quit small in cmarisn t its fr sac valu A 1.. On incrasing valu, radiatd wr in lctrmagntic md incrass cntinuusly but it always rmains lss than th fr sac valu vn fr an n circuit trminatin( 1. ). In lngitudinal lasma md, radiatd wr at ( A.) fr a matchd trminatin ( ) is lw but incrass cntinuusly u t 1. (n circuit trminatin). Th ttal wr radiatd ( P P ) in fr sac ( P ) is lw fr an n circuit trminatin. 4. Cnclusins Effct f th rsnc f lasma mdium n th diffrnt discntinuitis is bsrvd hr by cnsidring diffrnt lasma t surc frquncy ( ) valus. It can b cncludd frm th rsnt study that fr ratin in fr sac an n circuit discntinuity bttr than a matchd trminatin rating at vry high frquncis. In th lasma mdia, matchd trminatin is A -1 Figur 5. adiatin rsistanc in EM md and in lasma md fr diffrnt A and.7, (hm) Figur 6. (A=.) (A=1.) (A=.) (A=.95) and 1 1 (hm) fr diffrnt valus f and Cyright 9 Scis

6 186 Effct f Warm Inizd Plasma Mdium n adiatin Prrtis f Mismatchd Micrstri Trminatin bttr than an n circuit discntinuity bcaus ttal radiatd wr is lss fr matchd trminatin than an n ndd trminatin. Mr radiatins frm any discntinuity caus lss utility f that structur. Hnc, a matchd trminatin is suitabl with an antnna in lasma mdia thugh n circuit discntinuity suits mr in fr sac. A thrtical ffrt is mad hr in this cmmunicatin which rquirs xrimntal vrificatin, thugh simulatin f lasma mdia in labratry is vry difficult. EFEENCES [1]. E. Pst and D. T. Sthnsn, IEEE Transactins, AP P 9,19 P 133, [] J.. Jams and G. J. Wilsn, Micrwav tin and acustics, 1,165 P 174, [3] K.. Carvr and J. W. Mink, IEEE Transactins, AP 9, 14, [4] A. G. Drnryd, IEEE Transactins, AP 4, , [5] M. D. Abuzahra and L. Lwin, IEEE Transactins, MTT P 7,7 P 73, [6] D. Bhatnagar, Jurnal f Inst. Elctrnic and Tlcm. Engrs. 38, 13 P 16, 199. [7] M. V. Schnidr, Bll Systm Tch. J. 48, 141 P [8] A. M. Salm, D. Bhatnagar, J.f Plasma Physics, Vl.56, Pt.1, 5 P 34, Cyright 9 Scis