Development of ALMA Band 8 ( GHz) Cartridge

Transcription

1 Dvlopmnt of ALMA Band 8 (385-5 GHz) Cartridg Y. Skimoto 1,2,*, Y. Iizuka 1, N. Satou 1, T. Ito 1, K. Kumagai 1, M. Kamikura 1,2, M. Narus 1,2, and W. L. Shan 3 1 National Astronomical Obsrvatory of Japan, Tokyo , Japan 2 Univrsity of Tokyo, Dpartmnt of Astronomy, Japan 3 Purpl Mountain Obsrvatory, China * Contact: Skimoto.Yutaro@naoj.ac.jp, phon Abstract W hav dvlopd a cartridg-typ rcivr covring from 385 to 5 GHz for pr-production of ALMA Band 8. It rcivs two orthogonal polarizations and down-convrts th sidband-sparatd signals to intrmdiat frquncis (IF) btwn 4 and 8 GHz. Th cartridg-typ rcivr consists of a cold optics, a fd horn, an OMT, two sidband-sparating SIS mixrs, cryognic multiplirs of local oscillator (LO). Ths componnts wr individually tstd and thn th cartridg was intgratd and tstd as a complt assmbly. W hav also dvlopd quipmnt to tst both componnts and th intgratd rcivr. Th singl sidband (SSB) nois tmpratur of this rcivr is 13 K at th band cntr and 18 K at th band dgs. Th bam pattrn and cross-polarization pattrn ar consistnt with physical optical calculation. Ths rsults ar promising for rcivr production to th Atacama Larg Millimtr/submillimtr Array (ALMA). I. INTRODUCTION Th Atacama Larg Millimtr/submillimtr Array (ALMA) is an intrnational astronomy facility, built by Europ, North Amrica, and Japan in coopration with th Rpublic of Chil. ALMA, consisting of mtr diamtr antnnas and 16 Atacama Compact Array (ACA) antnnas, is locatd in northrn Chil at an lvation of 5 mtrs. Atmosphric windows from 3 GHz to 95 GHz ar covrd by 1 frquncy bands with rlativly wid bandwidth of 2 3 % [1][2][3]. Each frquncy band is obsrvd with a cartridg-typ rcivr rciving two orthogonal polarization. Th cryognic intrfac of th rcivr cartridgs for th ALMA was proposd by th Ruthrford Applton Laboratory (RAL) in UK[4]. Th cartridgs ar installd in a cryostat at th Cassgrain focus of th antnnas with som offst. Each cartridg contains cryognic rcivr optics or warm optics outsid of th cryostat toward th sub-rflctor. ALMA front nd dos not mploy a mchanical tunr xcpt for calibration dvic bcaus of oprational rliability. Th cartridg-typ rcivr contains optics, mixrs, amplifirs and local oscillators to achiv a modular concpt. ALMA cartridgs us a cartridg body providd by RAL and two cryognic multiplirs and a warm cartridg assmbly providd by NRAO, which includs a YIG oscillator, an activ multiplir chain, a bias modul, and a controllr. II. DESIGN A Cartridg Th ALMA Band 8 cartridg rcivs frquncis from 385 GHz to 5 GHz, which corrsponds to 26 % bandwidth with a cntr frquncy of GHz. Band 8 cartridg adoptd sidband-sparating (2SB) mixr of IF 4-8 GHz instad of doubl sidband (DSB) mixr of IF 4-12 GHz bcaus th atmosphr in th 4 GHz band has svral dp absorptions by H 2 O and O 2 [5]. To scap from ths dips, a sidband-sparating mixr is dsirabl for th Band 8 cartridg [6][7]. W hav dvlopd an ALMA Band 8 cartridg prproduction modl as shown in Figur 1 basd on xprinc of dvlopmnt of th qualification modl [8]. Th main diffrnc from th qualification modl is a wavguid OMT [8] as a polarization splittr. It has a fw advantags: 1. A rcivr optics at 4 K stag can b quit simpl and compact. An llipsoidal mirror, a corrugatd horn, and a wir grid can b rducd from th cryognic optics 2. Thr is no bam squint btwn two polarizations. 3. A concrn on thrmal cycl of a wir grid can b rsolvd. 253

2 Fig.1 ALMA Band 8 pr-production modl cartridg rcivr. Fig.2 Th 4 K stag of ALMA Band 8 pr-production modl cartridg rcivr. B Optics Th rcivr optics of th ALMA 12 m antnna is dscribd [1]. A physical optics calculation of th ALMA rcivr optics was mad [11] [12]. Thy us commrcial softwar, GRASP8 (TICRA Co.). W hav rpatd thir calculation with an updatd vrsion of GRASP9. A cryognic optics of this rcivr adopts a singl mirror to coupl a fd horn in front of an SIS mixr block and th sub-rflctor. An advantag of a singl mirror ovr two mirrors is that it is rlativly asy to align optical componnts of horns, mirrors and a wir grid. A disadvantag is that it is lss fr of mchanical dsign of th rcivr. A rflction angl at th mirror is 22.5 dgrs. Th optical paramtrs wr chosn as indpndnt at both th fd horn and th sub-rflctor in th frquncis of btwn 385 and 5 GHz. Th rcivr optics is inclind 1.6 dgrs toward th subrflctor. Th optics block was carfully dsignd mchanically to achiv optical paramtrs at 4 K. 1. to includ cryognic dformation of optics block at 4 K. 2. to allow mchanical masurmnts asily, svral rfrnc positions on th optics block ar addd. 3. to rduc wight to 59 grams, hols wr drilld in optics block. 4. to rduc standing wav btwn th subrflctor and th horn, an ara around th horn aprtur was hollowd out. Th optical block and mirrors wr mad of 661 aluminium (Fig.). Th alignmnt to th 4 K stag of cartridg body is dtrmind by two 2 mm dowl pins. Th block was masurd with a coordinatd machin, Mitsutoyo LEGEX91 and was consistnt with dsignd valus within typically 2 μm. A corrugatd horn for this rcivr was dsignd by [13][14]. Th dsign paramtrs ar horn diamtr of 7.99 mm, horn axial lngth of 24.1 mm, and horn slant lngth of mm. Th width and sparation of corrugation ar 9 μm. Th round tapr with 675 μm lngth conncts th throat of th corrugation with a diamtr of 68 μm and a circular wavguid with a diamtr of 568 μm, which is in turn smoothly connctd with a lngth of mm to a rctangular wavguid with 556 μm x 278 μm (WR2.2). This was fabricatd by lctroforming by Oshima Prototyp Enginring, Co. C OMT and Sidband Sparating Mixr (2SB) W hav dvlopd an ortho-mod transducr (OMT)[8] and a sidband-sparating (2SB) mixr [15]. To rduc wavguid transmission loss, an OMT and two RF quadratur hybrid / LO -17 db couplrs ar combind in a wavguid block as shown in Fig. 3. Th Band 8 prototyp OMT was a scald modl of Band 4 OMT [16], which has a Boifot junction and a doubl ridg for polarization sparation. It was optimizd for mchanical robust dsign of innr wavguid structur. It has low loss of -.4 db at 4 K and good polarization isolation of largr than 25 db [8]. Th sidband sparation schm is basd on th dsign dvlopd for th ALMA Band 4 cartridg[17]. Th Band 8 sidband sparation (2SB) mixrs hav bn dvlopd with wavguid quadratur hybrid [15]. Th cartridg rcivs both uppr and lowr sidbands as IF frquncis from 4 to 8 GHz. It mploys an RF quadratur hybrid and two singlndd DSB mixrs followd by an IF quadratur hybrid as shown in Fig.. W hav chosn to adopt a modular approach, which was originally proposd by [18] in which th DSB 254

3 mixrs and RF/LO couplr ar indpndnt. This allows th individual componnts to b tstd sparatly prior to intgration. In th modular schm, it is ssntial to stablish good intrfacs to intgrat ths componnts. RF OMT 32 mm 9dg Hybrid & LO couplr 9 Mixr lowr-ordr harmonics in th LO signal. Typical nois tmpratur of ALMA Band 8 DSB mixrs is shown in Fig.. A suprconducting magnt was usd for a DSB mixr to supprss th Josphson ffct. It consists of iron yoks and suprconducting wirs (Cu-cladding NbTi φ.7 mm) with 35 turns. It has 3 gauss with 1 ma currnt ] [K 1 r 8 tu ra p 6 m T 4 o is 2 N LO frquncy [GHz] Fig. 4 Nois tmpratur of ALMA Band 8 DSB mixrs. D Intrmdiat Frquncy (IF) Th Band 8 cartridg uss 4 cryognic low nois amplifirs (CLNAs) to amplify th IF signal btwn 4 and 8 GHz from two 2SB mixrs. It also uss 4 cryognic IF isolators (CISO) at th input of th CLNAs. Th CLNA mad by Nitsuki uss GaAs HEMT chip and is opratd with powr consumption of 8 mw at 4 K. Th nois tmpratur was 6 8 K with gain of 3 db. Two IF quadratur hybrids mad by Nitsuki ar mountd btwn th 2SB mixr and th CISO. Coaxial cabls btwn th mixr and th CLNA us phas-matchd on mad of coppr, whil othrs ar mad of stainlss stl (th cntral conductor is a silvr-platd cupronickl). Th phas diffrnc of th pair cabl is lss than 3 dgr. To compnsat frquncy-dpndnt loss of thrmallyisolatd coaxial cabls btwn 4 K and 3 K, warm IF amplifirs mad by AML hav an gain slop of 4 db from 4 GHz to 8 GHz. Th gain is 38 db and NF is lss than 1.5. Fig. 3 Uppr panl shows wavguid path of an OMT /RF quadratur hybrid / LO -17 db assmbly. Lowr panls shows outlook of ALMA Band 8 pr-production modl horn, OMT, 2SB mixrs assmbly. Th DSB mixr of this rcivr has bn dvlopd by [19]. Th SIS junction is mad of Nb and AlOx on a quartz substrat of 6 μm thicknss. It uss paralllly connctd twin junction (PCTJ) which has bn dvlopd by [2] and [21]. Th SIS junctions hav a currnt dnsity of 1 ka cm 2 or ωrc = 5 with a diamtr of 1.2 μm. Th input of a wavguid DSB mixr with 558 μm 229 μm (WR2.2) is rducd to a half of 58 μm x 127 μm at th SIS chip. This smallr siz was chosn to covr th RF frquncy btwn 385 and 5 GHz with cutoff frquncy for th fundamntal mod of around 3 GHz clos to th lowr RF frquncy limit, in ordr to minimiz th problm causd by unwantd E Local Oscillator (LO) Local oscillator for Band 8 cartridg has bn dvlopd and is providd by National Astronomy Radio Obsrvatory (NRAO) in USA. It consists of cryognic multiplir (x 6) opratd at 1 K and warm cartridg assmbly (g. [22]). Th output of th multiplir is transmittd with an ovrsiz wavguid (WR6.3) to th OMT/2SB assmbly. Th LO signal is coupld to RF signal at th -17 db couplr and trminatd with wdg-typ MF116 load. Th load dsign is basd on [23]. III. RECEIVER PERFORMANCE A Nois Tmpratur Nois tmpratur of a Band 8 pr-production prototyp cartridg was masurd with standard Y-factor mthod. 255

4 Ths tsts hav bn prformd with a cartridg tst cryostat [24]. Nois tmpratur was masurd with cryognic fifth tims multiplirs bcaus of its availability. Th outlin is th sam as sixth tims multiplir. Th multiplirs ar pumpd with a Gunn oscillator and a W-band powr amplifir covring frquncy 8 99 GHz. A choppr which changs hot and cold loads movs at 4 Hz. Fig. shows singl sidband (SSB) nois tmpratur of th Band 8 prproduction cartridg. SSB Nois Tmpratur [K] Frquncy [GHz] Fig. 5 SSB nois tmpratur of ALMA Band 8 pr-production cartridg. In ALMA spcification, SSB nois tmpratur is lss than 196 K ovr 8 % of th frquncy rang and lss than 292 K at any frquncy from 385 to 5 GHz. B. Imag rjction ratio (IRR) Imag rjction ratio (IRR) was masurd with a mthod using an xtrnal signal sourc [25]. Th RF signal from th sourc is coupld quasi-optically to hot and cold loads. Optics for both Y-factor and a signal sourc was dsignd with 5 tims of Gaussian bam radius. Thy ar frquncyindpndnt at th horns. Th IRR was largr than 1 db as shown in Fig ) B3 (d a tio 25 R n 2 c tio j 15 R a g1 Im Frquncy (GHz) Fig. 6 Imag rjction ratio of ALMA band 8 pr-production cartridg. Th ALMA spcification of IRR is largr than 1 db. C. IF spctra IF Output (dbm/8mhz) CW1 46 GHz_Pol._USB Gunn; Radiomtr S/N Magnt = 11 ma Hot Cold Nois Tmp. Frquncy (GHz) Fig. 7 Typical IF spctrum of ALMA Band 8 Pr-production cartridg at th LO frquncy of 46 GHz. A typical spctrum of th IF output is shown in Fig.. This is masurd with a spctrum analyzr. Th output powr in th IF spctra has a gain slop bcaus warm IF amplifir has a positiv gain slop of 4 db from 4 GHz to 8 GHz. Th ALMA spcification of gain variations in any 2 GHz is lss than 4 db. Band 8 pr-production cartridg can comply it in most of frquncis, but thr ar som frquncis which has largr variation than this spcification. D. Bam masurmnts Bam pattrn and Cross polarization pattrn of Band 8 pr-production cartridg optics hav bn prsntd by [26]. Th masur bam pattrns ar consistnt with physical optics simulations at 385, 442, and 5 GHz. Th cross polarization lvls at 385, 442, and 5 GHz, ar lss than - 23 db. Th main sourc of cross polarization was th OMT. E. Othr prformanc Othr prformanc such as gain comprssion, amplitud stability, and phas stability was masurd with Band 8 QM cartridg [8]. Gain comprssion was lss than 1 db. Th amplitud stability was around 3x1 4 in 1 sc. Th phas stability was lss than 2. dgrs on a timscal from.1 sc to 1 minuts. F. CONCLUSIONS W hav dvlopd a prototyp of ALMA Band 8 cartridg rcivr as wll as its tst quipmnt. Th cartridgtyp rcivr includs cold optics, a fd horn, an OMT, two 2SB mixrs, cryognic multiplirs, cryognic and warm IF amplifirs. Ths componnts wr individually tstd and thn th cartridg was intgratd and tstd as a complt assmbly. W hav also dvlopd quipmnt to tst both componnts and th intgratd rcivr. Th singl sidband (SSB) nois tmpratur of this rcivr is 13 K at th band cntr and 18 K at th band dgs. Th bam pattrn and cross-polarization pattrn ar consistnt with physical optical calculation. Ths rsults ar promising Tssb (K) 256

5 for rcivr production to th Atacama Larg Millimtr/submillimtr Array. ACKNOWLEDGMENT W thank ALMA front nd IPT lad by Gi Han Tan, John Wbbr. Th authors also thank Takashi Noguchi, Tomonori Tamura, Shi-Cai Shi, Junji Inatani, Gnshiro Fujii, Shin ichiro Asayama, Yoshi Uzawa, Masahiro Sugimoto. This work was partially supportd by Grant-in-Aid of JSPS No REFERENCES [1] Brown, R. L., Wild, W., and Cunningham, C. 24 Advancs in Spac Rsarch 24, 555 [2] R. Hills Submillimtr intrfromtrs: nw standards for futur instrumntation, Proc. Of 19 th Int. Symp. on Spac Trahrtz Tch., 28 [3] G. H. Tan Th ALMA front nds : an ovrviw Proc. Of 19 th Int. Symp. on Spac Trahrtz Tch., 28 [4] Orlowska, A., Harman, M., and Ellison, B. ALMA Projct Book, chaptr 6, 22 [5] S. Matsushita, H. Matsuo, J. R. Pardo, S. Radford, FTS Masurmnts of Submillimtr-Wav Atmosphric Opacity at Pampa la Bola II : Supra-Trahrtz Windows and Modl Fitting PASJ, 51, 63, 1999 [6] Guillotau, S. ALMA mmo 393 DSB vrsus SSB and Bandwidth/Snsitivity tradoff, 22 [7] Iguchi, S. PASJ 57, 643, Radio Intrfromtr Snsitivitis for Thr Typs of Rciving Systms: DSB, SSB, and 2SB Systms, 25 [8] N. Satou, Y. Skimoto, Y. Iizuka, T. Ito, W. Shan, T. Kamba, K. Kumagai, M. Kamikura, Y. Tomimura, Y. Srizawa, S. Asayama, M. Sugimoto, A Submillimtr Cartridg-Typ Rcivr: ALMA Band 8 (385-5 GHz) qualification modl, Publication of Astronomical Socity of Japan in prss 28 [9] M. Kamikura, M. Narus, S. Asayama, N. Satou, W. Shan, Y. Skimoto Dvlopmnt of a GHz Orthomod Transducr (OMT), Proc. Of 19 th Int. Symp. on Spac Trahrtz Tch., 28 [1] Cartr, M. C. t al. 24 SPIE, 5489, 174, ALMA front nd optics [11] Tham, C. Y., Withington, S. 23, Rcivr Optics Dsign Elctromagntic Analysis, Scond Rport (Bands 3, 6, 7 and 9) [12] Tham, C. Y., Withington, S. 23, Rcivr Optics Dsign Elctromagntic Analysis, Third Rport (Bands 4, 8 and 1) [13] Matsunaga, M., Skimoto, Y., Matsunaga, T., Sakai, T. 23 PASJ 55, 151 An Exprimntal Study of Submillimtr-Wav Horn Antnna for a Submillimtr-Wav Astronomy [14] Matsunaga, M., Matsunaga, T., Skimoto, Y. 24 Procdings of th SPIE, Vol. 5445, 446 Analysis of submillimtr-wav horn antnnas for submillimtr-wav tlscop [15] M. Kamikura, Y. Tomimura, Y. Skimoto, S. Asayama, W. L. Shan, N. Satou, Y. Iizuka, T. Ito, T. Kamba, Y. Srizawa, T. Noguchi A GHz Sidband-Sparating (2SB) SIS Mixr Basd on a Wavguid Split-block Couplr Intrnational Journal of Infrard and Millimtr-Wav 27 (1), 37, 26 [16] S. Asayama, S. Kawashima, H. Iwashita, T. Takahashi, M. Inata, Y. Obuchi, T. Suzuki, and T. Wada Dsign and Dvlopmnt of ALMA Band 4 Cartridg Rcivr, Proc. Of 19 th Int. Symp. on Spac Trahrtz Tch., 28 [17] Asayama, S., Ogawa, H., Noguchi, T., Suzuki, K., Andoh, H., Mizuno, A. ALMA mmo 453, 23 [18] Claud, S. M. X., Cunningham, C. T., Krr, A. R., and Pan, S.-K. 2, ALMA mmo 316 Dsign of a Sidband-Sparating Balancd SIS Mixr Basd on Wavguid Hybrids [19] Shan, W. L., Shi, S. C., Noguchi, T., Skimoto, Y. 25 IEEE trans. Applid Suprconductivity 15, 53 Dsign and Dvlopmnt of SIS Mixrs for ALMA Band 8 [2] Noguchi, T., Shi, S. C., and Inatani, J. 1995, IEEE applid suprconductivity, 5, 2228 An SIS mixr using two junctions connctd in paralll [21] Shi, S. C., Noguchi, T., Inatani, J IEEE Trans. on Applid Suprconductivity, 7, 2587 Dvlopmnt of a 5-GHz band SIS mixr [22] E. Bryrton, J. Hslr Sidband nois scrning of multiplir-basd sub-millimtr LO chains using a WR-1 Schottky mixr, Proc. Of 19 th Int. Symp. on Spac Trahrtz Tch., 28 [23] F. P. Mna, A. M. Baryshv, Dsign and Simulation of a Wavguid Load for ALMA-band 9, ALMA mmo 513, 25 [24] Skimoto, Y. t al. 23 ALMA mmo 455 Cartridg Tst Cryostats for ALMA Front End [25] Krr, A.R., Pan, S.-K., and Effland, J.E. 21, ALMA Mmo 357, Sidband Calibration of Millimtr-Wav Rcivrs [26] M. Narus, M. Kamikura, Y. Skimoto, T. Ito, M. Sugimoto, Y. Iizuka, N. Satou, K. Kumagai Nar fild bam and cross-polarization pattrn masurmnts of ALMA band 8 cartridgs, Proc. Of 19 th Int. Symp. on Spac Trahrtz Tch.,