Line width of Josephson flux flow oscillators V.P. Koshelets a,b, * , P.N. Dmitriev a , A.S. Sobolev a , A.L. Pankratov c , V.V. Khodos c , V.L. Vaks c , A.M. Baryshev b , P.R. Wesselius b , J. Mygind d a Institute of Radio Engineering and Electronics (IREE), Mokhovaya 11, GSP-9, 101999 Moscow, Russia b Space Research Organization of the Netherlands, 9700 AV Groningen, The Netherlands c Institute for Physics of Microstructures, GSP-105, 603950 Nizhny Novgorod, Russia d Department of Physics, Technical University of Denmark, B 309, DK-2800 Lyngby, Denmark Abstract A combination of wide-band electronic tunability and moderate free-running line width makes the Josephson flux flow oscillator (FFO) a perfect on-chip local oscillator for integrated submillimeter-wave SIS receivers. The possibility of FFO phase locking at all frequencies of interest has to be proven before one initiates real FFO applications. To achieve this goal a comprehensive set of line width measurements of the FFO operating in different regimes has been performed. FFOs with tapered shape have been successfully implemented in order to avoid the superfine resonant structurewithvoltagespacingofabout20nVandextremelylowdifferentialresistance,recentlyobservedintheIVCof thestandardrectangulargeometry.TheobtainedresultshavebeencomparedwithexistingtheoriesandFFOmodelsin order to understand and possibly eliminate excess noise in the FFO. The intrinsic line width increases considerably at voltages above the boundary voltage because of the abrupt increase of the internal damping due to Josephson self- coupling. The influence of FFO parameters, in particular the differential resistances associated both with the bias currentandwiththeappliedmagneticfieldontheradiationlinewidth,hasbeenstudied.Possiblemeansofdecreasing the free-running FFO line width will be discussed. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 07.57.K; 07.57.H; 85.25; 85.25.N Keywords: Superconducting submillimeter-wave receivers and detectors; Superconducting integrated circuits; Superconducting submillimeter-wave oscillators 1. Introduction Thesuperconductingintegratedreceivers(SIRs) [1,2] with low power consumption are very at- tractive for both radio-astronomical research and remote monitoring of the Earth atmosphere in the submillimeter-wave range. A lightweight and compact ultra-sensitive submillimeter SIR is a sin- gle-chip device, which comprises an SIS-mixer with a quasioptical antenna and a superconduct- ing local oscillator. Flux flow oscillators (FFOs) [3] are presently being developed for integration with SIS-mixers for use in submillimeter wave all- superconductorintegratedreceivers[1,2].TheFFO Physica C 372–376 (2002) 316–321 www.elsevier.com/locate/physc * Corresponding author. Address: Institute of Radio Engi- neering and Electronics (IREE), Mokhovaya 11, GSP-9, 101999 Moscow, Russia. Tel.: +7-095-203-2784; fax: +7-095- 203-8414. E-mail address: valery@hitech.cplire.ru (V.P. Koshelets). 0921-4534/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S0921-4534(02)00659-7