Документ взят из кэша поисковой машины. Адрес оригинального документа : http://www.cplire.ru/html/lab234/Tarasov/reprints/IEEEtransMAG81p819.pdf Дата изменения: Sat Mar 12 19:51:35 2005 Дата индексирования: Sat Dec 22 11:32:00 2007 Кодировка: Поисковые слова: universe

IEEE TRANSACTIONS ON MAGNETICS, VOL. MAG-17, NO. 1, JANUARY 1981

819

POINT CONTACTS V.P,D'yakov, V.N.Gubankov, M.A.Tarascw, A,N,Vystavkin The Institute of RadioEngineeringandElectronics of the Academy of Sciences of the USSR Moscow CSP-3, PBBrx-avenue, 18
1. Experimental research directed to making more accurate the existing idea about theJosephsonfrequencydownconverteroperation is reported in this paper. The limits when the converter operation qualitatively differs from usual theoretical model are investiga.te4, The Josephsonconverter operation peculiarities connected with con$act I-V-curve deformation by radiation are COPsidered. It's reportedabouttheperformance of the first sample of the F-band Joaephs'on superheter odyne radiometer .The radiometer passed radiotelescope tests successfully. 2, The model proposed by Grimesand Shapiro is usually used for considering the frequency conversion process (Pig, I1.

FREQUENCY CONVER@ION OF MILLIMETER RADIATION TO X-BAND WITH SUPERCONDUCTING

@PC) I-V-curves. The deviation from G-S-model haabeen observed for SPC with a normal resistance R <'I5 Ohm and a characteristic voltage V ,< 150pV,Therehavebeen two isolated convgrsion efficiency maxima' between neighbouringheterodyneconstantvoltagesteps for SPC with theseparameters. Dependences, of the converted signal power aa a function of ihe gontact constant oiltag$ for cases-f p f (solid line) and f < f (dashedlinelare showed fn Fig.2.
Nb-Nb and Nb-& with non-hysteretic

usedsuperconductingpointcontacts

v

TI

f
O

\-

JV)

m

I

,--c-----

Fig,?, The Grimes-Shapirofrequencyconversion mechanism model, The result amplitudemodulated oscillation ("An) influence t o the contact leads t o appearance of the IF voltage component on thecontact ("B") if the low-frequency contact current component is fixed(tgS>>R). In this model it's supposedthat: 1) the sum of lowpower signal andhighpower heterodyne oscillations' may be presented as a single 2) the reamplitude-modulatedoscillation; sult amplitude-modula ted oacilla t ion influence leads t o the heterodyne steps appearing on the I-V-curve only moreover steps eizes change with the intermediatefrequency (IF). Obviously the conversion beheviour should be i dependent on a sign of the difference (fs-fx) w i hin Grimes-Shapiro (G-S) model, where f S , are signal andheterodyne frequencies corresponding y.However we have observed spch dependence when the X-band intermediatefrequencyas been used, The frequencies 3 72GGz and fs = 54 GGz were beingbonverted intofif= &7 GGz. In our experimentstherewerebeing

.fth

,P

h

h h are conHeterodgne power P and frequencyiSf is the staat, One can see there on V= where 483 MGz ,uV maximurn apart from the -Ptf maximum corresponding the step bias. The sigqalfrequencydialac n on 2.f displacee its 'fi: position on 2J0 f$&bzing dieplacedtothesymmetrical(about f= const) frequency asymmetry of the de endence Plf (VI in reapect of the difference !fs-fh) sign is ob erved too. This asymmetry has been explained in the resistively shunted junctionmodel'frameworkforthecaae whe the Josephson radiation linew dth Af'Kf?. In accordancewiththe work when Afy
eo+%,

$zq==

P

3

3

0018-9464/81/0100-0819$00.75 0 1981 IEEE


820

been observedexperimentally 3. The came of the asymmetry depictedabove is thechanging of signal andheterodynefrequency combination responsible for the synchronization of Jose hson radiation when f5 is displaced t o tge symmetrical(about -fh ) frequency. In order t o con-vince ourselves that the specified phenomena doesn't result in violawe tion of the signal conversion coherence have compared dependences p'@)in case 09 the parallel signal processing in narrow and broadbandwidthchannels. These dependences having been identical the immediate participation of the contact Josephson radiation in the fr-equencgconveraionprocessincase Af3sf'f doesn't result in an appearance of a noncoherence component in the converted signal. The G-S-model is also inapplicable in the other limit: when Af3S-fh3. In this case heterodyne steps doesn't form and SPC behaves as a usual nonlinear element,that is t o say SPC Pa completelydescribedwith its I-V-curve form. We haveobservedsuchbehaviourfor SPC with R >r 200 Ohm and it was accompanied by aha p conversion efficiency decrease (Fig.3 1. The latter has probably been cauaed

T

P" (orb. untts~

signal is more intricate. In thepresence of an external radiation the contact I-TI-curve changes its shape. Specifically SPC rd changes rd changing results in in the working point. changingthematchingregime of the IF amplifier with the contact. Moreover the baokground radiation part coming t o the contact by the IF line and peflected by the contact changes. In this 'case the maximum signal corresponds t o thebiasnear a step. tlembryov' begining t o form on the voltage corresponding. t o f s Since for a small input signal the influence upon I-V-c rve is proportional t o thesignal power Ps it is impossible t o distinguish this type of an interaction .$ram the ttoscillator-mixern conversion from P' (P? dependenceappearance, However in the case when the receiver is construc,ted as usual one with an input modulator and an synchronous detector in ita output making outspecified signal is a success in a number of cases.Since rd changes t o different direcon the centre and the tions for the biasea edges of the step the signals of different polaritjes may form on the receiver output ) butthat is obviously impossible (Pig.4 in case of woscillator-mixern.

.

5

3

rA

I
e

.I

Pig.3. The converted signal power dependence on R for a constant signal power and optimal choice of a heterodyne power andbias. The contact is placed in the 3,6x1,8 mm waveguide with a shorting plunger. by the SPC I-V-curve curvature decreasing owing t o fluctuations influence increasingly when R increase. 3. Sincefluctuationsplaystheimportant o eration we art in the Josephson converter !ave measured the SPC intrinsic ffuctuation level to concretize therequirements upon a of anexternalinterference filteringdegre SIX with R=50+120 Ohm have on the contact been investigated. According t o Fig.3 these SPC correspond t o theconverterparameters closed t o optimum. The measurementshavebeen carried out under conditions when any electromagnetic interference in contact and the thermal background radiation havemight be neglected in comparison with the contact intrinsic fluctuation. The fluctuation current diaperaion measuredunder this conditions according t o I-V-curve smearinghas been from 0.4 to 1 9 A . Thus there is no point in decreasing of interference level below 0.2pA in real conditions. 4. When the heterodyne radiation is absent the appearance of the output signal in a Joaephsonsuperheterodyne is usuaLly connected with noscillator-rnjxer'l conversion only 5. However the real structure of that

4.

Fig.4. A typical dependence of the res onse on the modulated receiver output when a monochromatic signal influences upon the low-resistance contact. On Fig.4, besides output peaks in the step-region there is the two-polarity peak in V%Qo fi.f'region, The latter is observed for the case of the work in the current sourceregime and for small R contacts when af'<< -fS The cause of this peak appearance is the Josephson radiation penetration in the IF amplifier pass-band. The synchronous forms owing t o the detector output signal Josephson radiation spectrum changes with modulation frequency under the input signal influence. R increasing the specified peak merges with the other ones. As in case SPC rd changing as in case SPC Josephson radiation spectrum changing and the IF amplifier behave as system"detector-amplifier of the "modulator-demodulatorrltypfrvl but not as ansuperheterodyne. It is sxmple t o ahow this systemhassuch limiting sensitivity as an usual Josephson detector has. 5. We haveproduced the P-band superheterodyne radiorn ter with the Josephson mixer on the input The radiometer the haa input diagram modulator, The commercially available E-band generator G4-104 and the sen!iconductorfrequencydoubler have been used as an heterodyne. The transistor amplifier with the paas-band from 200 t o 400 MGz has been used as the IF one. The IF amplifier input noise temperature having been 3QOK we mixer havenot been able t o use the Josephson

V

8

.

(.


821

limiting possibilities completely. The resonant fris has been installed in immediately front of the mixer for decreasing of an background influence and wrong channels eliminaKa' I tion. The mixer has beenplaced in the tranaDort helium Dewar vessel with volume 10 litre. $PC Nb-Nb has beenformed in Liquid helium directly. Contacts forming and their characteristics adjusting were made with the rod which was manipulatedout of dewar. The dewarwas allowingus t o carry out continuousmeasuringduring two dags. The optimum results havebeen obtained for contacts with resistances R = 15'80 Ohm, V, =300+600)V and non-hysteretic I-V-curves. SPC has beenplaced in the narrowingwaveguide. The constant current and audio freI quenciesshuntwithresistance 1 Ohm has been switched in parallel with the SPC. It was allowing t o set a bias with a voltage source. Thereby we havebeen a success in essential decreasing of the SPC parametersdeviation Fig.5. The solar radiation recording with a parasiticheterodyne power changing. (upper) and the lunar one (lower)carried A parasitic shanging of in radiometer an out 28.03.79. The numbers on the figure with a modulator arises because of an hetethe time of theobservation. The obserrodyne power part penetrating into the input 1003 BaBr, vationconditiong:pressure modulator. In this case an interference with humidity 4.1 g/m , ten-tenthscloud,fine forms on the radiothemodulationfrequency snow. meter input. The interference arising causes are the same that havebeen considered in REFERmCES p.4. C.C.Grimes, S.Shapiro, Physical Review, The drastic measure of the interference 6 ,397 (1968) eliminating ia an isolator putting in the .Vystavkin, V.N.Gubankov, V.P.D'yakov, signalchannel. However the high loss in the A.M.Spitzin, Radiotekhnika i Elektronika, F-band isolators has forced u8 to give up 22 2641 (1977) (in Russian) onesusing.Decreasingthesynchronousintere.Dtyakov, K.K.Likharev, H.A.Tarasov, ference t o the acceptable level besides the 1736 Radiotekhnika i Elektronika, 2& SPC shunting on the modulation frequency we (1980) (in Russian) have taken action for decreasing of the heA.I.Vystavkin, V.N.Gubankov, V.P.D'yakov, interodyne radiation penetration into the I.A.Tarasov. "InvestiRation of JoseDhson putmodulator. With this purposetheheteroconvertor with the microwave IF", pieprint of IREE AS USSR N 21 (277)s lioacow (1979) dyne radiation has beenbrought t o SW through the separate channel. The coupling (in Russian). between the signa1 channel and the heterodyne G.Vernet, R.Adde, J.App1. Phys., 4f1.,2678 flowone has been realized with the current (1974). ingthrough SPC only and therebythecoupling K.K.Likharev, B.T.Ulrich, Y3ystems with has been reduced t o minimum. Josephsoncontacts.Basises of the theory!: The radiometer has been used for carring MOSCOW, MOSCOW university (1978) (in Rueout of radioastronomicalobservations on &he s ian) radiotelescope RT-25x2 (Gorki). On Fig.5 A.I.V~stavkin. V.N.Gubankov. V.P.D'~akov. of the solar and luthere are the recordings 198 Radiotekhnika i Elektronika ; nar radiation carried out with this radiome(1979) (in Ruseian) .. ~- .~ of the ter. The root-meansquareinputnoise V,S,Abljazov, S.A.Andreev, V.P.D1yakov, radiometer was 0.3 K (DSB) for poetdetection A.I.Gukov, V,N.Gubankov, K.A~Rulow, rise time I s (the best result was 0.12 M.A.Tarasov, S.Yu.Turygin, A.M.Vyetavkin, The radiometer has sensitivity as high as RadioA.G.Kisllakov. V.I.Chernvshow one best up-dag P-bend superhete odyne used tekhnikali Elektionika, &7to be'publimore better IF amplifier though In future shed (in Russian) we hope t o realize the radiometer Sensitivity H.I.Cong., A.R.Kerr, R.Bdattauch, MFT, about 0.02 K using more sensitive IF amplifier. WIT-27 9 245 ( 1979)

-

43

a,

~

~

IC).

5.

.