Narrow-wall slotted waveguide array antenna with low cross-polarization filter

Transcription

1 6th Intrnational Confrnc on Machinr, Matrials, Environmnt, Biotchnolog and Computr (MMEBC 06) Narrow-wall slottd wavguid arra antnna with low cross-polarization filtr Guoan Xiong, a, Jin Pan, b and Bouan Ma, c School of Elctronic Enginring, Univrsit of Elctronic Scinc and Tchnolog of China, Chngdu 673, China; Yingcai Honor Collg, Univrsit of Elctronic Scinc and Tchnolog of China, Chngdu 673, China; a gustav_xiong@foxmail.com, bpanjin@ustc.du.cn, c @qq.com Kwords: slottd wavguid antnna, arra, cross-polarization, filtr. Abstract. A narrow-wall slottd wavguid arra antnna with low cross-polarization filtr is prsntd. Th horizontal polarization (HP) is th co-polarization for narrow-wall slottd wavguid arra antnna, whil th vrtical polarization (VP) is th cross-polarization. High lvl cross-polarization rducs ffct and is undsirabl. Som formulas wr prsntd to giv a concis xplanation how this structur rducs cross-polarization. On this basis, a 3-lmnt low cross-polarization narrow-wall slottd wavguid arra antnna in 9.305GHz was dsignd and simulatd. Th antnna has th charactristics SLL=-0dB and cross-polarization lowr than -40dB.. Introduction Th slottd wavguid arra antnna is usd in radar tchnolog and communications bcaus of high gain prformanc, low lvl scondar bams, manufactur cost and low loss. Slots ar fabricatd in narrow walls or wid walls. For narrow-wall slottd wavguid arra antnna, th slant slots with diffrnt angls and dpths must intrrupt th surfac currnts to radiat TE 0 mod wav. Th slant slots mainl radiat horizontal polarization wav, whil vrtical polarization wav is also radiatd from thm. Cross-polarization in such antnna is not nglctabl, which caus additional lobs in azimuth pattrn. For th purpos of dcrasing undsird cross-polarization in narrow-wall slottd wavguid arra antnna, som mthods hav bn prsntd. Using polarization filtr is th simplst wa to rduc cross-polarization []. A kind of polarization filtr is consistd of orthogonal walls btwn slots. B choosing distanc btwn two adjacnt orthogonal walls, vrtical polarization can b dcrasd. Anothr simpl polarization filtr was also dvlopd. It is consistd of a lar that man mtal strips ar printd []. B choosing width of strips, distanc btwn mtal orthogonal strips and thicknss of lar, this filtr has minimal influnc on horizontal polarization whil significant influnc on crosspolarization. Man nw structurs wr dvlopd to dcras cross-polarization. A pair of shapd iriss that flanks th slot in th wavguid is dsignd to rduc cross-polarization lvl [3]. Th cross-polarization lvl is lss than -40dB in an arra with 6 such lmnts. B insrting slant ridg undr th slots, slots can b rct which onl radiat horizontal polarization signal [4]. Basd on rcnt rports, it sms that most of th works rportd on low cross-polarization narrow-wall slottd wavguid arra antnna hav focusd on mthods to dsign it. But th phsical principl and calculation mthod ar not rportd sstmaticall. In this papr, th narrow wall slottd wavguid arra antnna with low cross-polarization rctangular wavguid filtr is dsignd and simulatd b HFSS. Th dsignd arra antnna has charactristics cross-polarization lowr than -40dB and SLL=-0dB. 06. Th authors - Publishd b Atlantis Prss 705

2 . Antnna Dsign. Polarization Filtr Dsign. Fig. Narrow-wall slottd wavguid arra antnna with rctangular wavguid polarization filtr and its E fild distribution Fig. Tim-harmonic currnt in smi-unboundd rctangular wavguid sstm Th rctangular wavguid polarization filtr is shown in Fig.. B mans of Babint's principl [5], man of th problms of slot antnnas including slottd wavguid antnna can b rducd to situations solving complmntar linar antnnas for which solutions hav alrad bn obtaind. For narrow wall slottd wavguid arra antnna, E fild is shown in Fig.. In Fig., E fild can b dcomposd into E H and E V. B th mans of Babint's principl, E H can b xcitd b I H in horizontal lctric dipol antnna, and E V can b xcitd b I V in vrtical lctric dipol antnna. In a wavguid sstm, whn th oprating frqunc is lss than th cutoff frqunc of TE 0 wav (f<f c ), TE 0 wav mustn't propagatd. Thr is th sam E fild distribution btwn TE 0 wav in a rctangular wavguid sstm and vrtical lctric dipol antnna. For th purpos of rducing E V (cross-polarization), th condition as bllow must b fulfilld to nsur th falloff of TE 0 mood, b < λ () whr: b-lngth of narrow wall of wavguid filtr; λ -lngth of lctromagntic in a fr spac To nsur th propagation of TE 0 mood (co-polarization), th condition as bllow must b fulfilld a > λ () whr: a-lngth of broad wall of wavguid filtr; λ -lngth of lctromagntic in a fr spac In ordr to nsur th cross-polarization fild in this kind of sstm, slots can b rgardd as th xcitation sourc for abov smi-unboundd rctangular wavguid sstm in Fig.. E fild xcitd b dirction currnt J(r') in (x',',z') can b prsntd b lctric dadic Grn function of th first kind as follows Er ( ) = jωµ G ( rr, ') Jr ( ') dv ' (3) V B dadic Grn functions in lctromagntic thor, w obtain G( rr, ') kg( rr, ') = δ ( r r') (4) Th dirction of th vctor magntic potntial xcitd b dirction currnt J(r') in wavguid is along with axis. Thus, this problm can b simplifid using potntial dadic Grn function G( rr, ') and potntial scalar Grn function b (5)-(7). Th boundar conditions ar shown in (8) 706

3 G ( rr, ') = ( + ) G( rr, ') (5) k G( rr, ') = G( rr, ') (6) Grr + kgrr = x x z z (7) (, ') (, ') δ( ') δ( ') δ( ') G( rr, ') x= 0, az ; = L= 0 G( rr, ') (8) = 0, b = 0 B mthod of ohm-raligh, potntial scalar Grn function G( rr, ') can b prsntd as (9), so using (5)-(6), lctric dadic Grn function G (, ') rr is shown in (0). Th co-polarization E fild xcitd b slots in rctangular wavguid sstm can b calculatd from (3) γ ' δ ' 0 π π ' π π ' γ n n x n x m m sh z z G( rr, ') = sin sin cos cos γ = = 0 γ ab m n mn a a b b shγ ' z z' (9) G(, ') G(, ') G(, ') G ( rr, ') = rr x + [ G(, ') + ] + rr rr rr z (0) k x k z mπ nπ n = 0 whr: γ mn = ( ) + ( ) k ; δn0 = a b 0 ls. Arra antnna Dsign. Fig. 3 shows th structur of 3-lmnt slottd wavguid arra antnna with rctangular wavguid cross-polarization filtr. BJ00 wavguid (a=.86mm, b=0.6mm, t=.7mm) is chosn to b slottd. Th filtr is mad up of FR4 lar with coppr of 0.08μm on it. Tabl shows th structur paramtrs. B Talor snthsis mthod, th amplitud of ach slot in 3 lmnts of SLL=0dB can b gt. Th quivalnt normalizd conductivit distribution is also calculatd b [6] as Fig. 4(a). Th quivalnt normalizd conductivit distribution is th maximum at an angl among diffrnt dpths. Using (), th rlationships among angl, quivalnt normalizd conductivit g and slot dpth can b simulatd b HFSS. Th corrspondnc among angl, quivalnt normalizd conductivit g and slot dpth can b shown in Fig. 4(b). Using Fig. 4(a) and 4(b), th angl and dpth of ach slot can b sur. d S α N g = ( ) () S whr: α-wavguid loss pr unit lngth; N-numbr of slots Tabl Structur Paramtrs d da db dc w 4mm 50mm mm 5mm.5mm Fig. 3 Slottd wavguid arra antnna with rctangular wavguid cross-polarization filtr 707

4 Fig. 5 shows th simulatd radiation pattrn in horizontal plan in 3-lmnt slottd wavguid antnna with cross-polarization filtr in GHz. Th simulatd maximum sid lob lvl is -0dB with cross-polarization lvl of -40dB blow th main lob in th band. (a) (b) Fig. 4 (a) Equivalnt normalizd conductivit distribution (b) Corrspondnc among angl, quivalnt normalizd conductivit g and slot dpth 3. Summar Fig. 5 Simulatd radiation pattrn in horizontal plan in 9.305GHz In this papr th calculation of cross-polarization in rctangular wavguid cross-polarization filtr is rportd. On this basis, 3-lmnt narrow wall slottd wavguid arra antnna in 9.305GHz with this filtr is dsignd and simulatd b HFSS. Th lvl of cross-polarization lobs blow th main lob is lowr than -40dB with th maximum sid lob lvl of -0dB, allowing this antnna adapt to radar sstm. Rfrncs []. M. Mazur, J. Wisniwski. "Prformanc of cross-polarization filtr ddicatd for slottd wavguid arra antnna." IEEE National Radar Confrnc. Arlington, Virginia, USA, 0-4, Ma, 00, p []. L. B. Whitbourn, R. C. Compton. "Equivalnt-circuit formulas for mtal grid rflctors at a dilctric boundar. " Applid Optics. Vol. 4 (985) No., p [3]. W. Wang, J. Jin, J. G. Lu, t al. "Wavguid slottd arra antnna with broadband, dual-polarization and low cross-polarization for X-band SAR applications." IEEE Intrnational Radar Confrnc. Arlington, Virginia, USA, 9-, Ma, 005, p [4]. A. Mallahzadh, S. Mohammadalinzhad. "An Ultralow Cross-Polarization Slottd Wavguid Chbshv Arra Antnna." Europan Confrnc on Antnnas and Propagation. Rom, Ital, -5, April, 0, p [5]. H. G. Bookr, "Slot arials and thir rlation to complmntar wir arials (Babint's principl)." Elctrical Enginrs - Part IIIA: Radiolocation. Vol. 93 (946) No. 4, p

5 [6]. A. F. Stvnson, "Thor of Slots in Rctangular Wav Guids." Journal of Applid Phsics. Vol. 9 (948) No., p