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Träfflista för sökning "WFRF:(Vassilev Vessen 1969) ;pers:(Dochev Dimitar Milkov 1981)"

Sökning: WFRF:(Vassilev Vessen 1969) > Dochev Dimitar Milkov 1981

  • Resultat 1-9 av 9
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1.
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2.
  • Belitsky, Victor, 1955, et al. (författare)
  • Terahertz Instrumentation For Radio Astronomy
  • 2009
  • Ingår i: International Symposium on Terahertz Science and Technology between Japan and Sweden. ; , s. 28-29
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • Radio Astronomy was always a frontrunner in the demand on terahertz technology. Millimetre and sub-millimetre wave receivers operate at ground-based observatories for more than 20 years with real Terahertz instruments making its way to ground-based [1] and space-based observatories, e.g., Herschel HIFI, during last years.In this talk, we will look at the key requirements to the radio astronomy and environmental science terahertz receivers using heterodyne technology. The most promising and established technologies for high-resolution spectroscopy instrumentation will be discussed. Using results of the Group for Advanced Receiver Development for Onsala Space Observatory 20 m telescope, for Atacama Pathfinder Experiment (APEX) telescope and ALMA Project Band 5, we will illustrate the trends and achievements in the terahertz instrumentation for radio astronomy.
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3.
  • Dochev, Dimitar Milkov, 1981, et al. (författare)
  • Superconducting IF biasing circuit for low-noise cryogenic applications
  • 2010
  • Ingår i: Journal of Physics: Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 234:4
  • Konferensbidrag (refereegranskat)abstract
    • A planar superconducting circuit designed for use in low-noise cryogenic applications is presented. The circuit is a bias-T combined with a 4–8 GHz impedance matching circuitry, which employs entirely planar design with a novel layout. The proposed and tested circuitry is intended to be used with a SIS mixer and incorporates a double section transformer based on microstrip line technology with a total impedance transformation of 5:1 within the frequency band. One of the transformer sections employs a three-line coupled line, which also serves as a DC block capacitor. The microstrip lines were manufactured using superconducting Nb metallization, which provides a conduction loss-free solution at the operation temperature of 4 K. S-parameter measurements at 4 K temperature were performed and found to be in a good agreement with the simulations. The device measured return loss is better than −10 dB within the frequency band. Furthermore, the circuit was tested as a part of 385 – 500 GHz double sideband heterodyne SIS receiver demonstrating a flat noise temperature response of 80 – 90 K over the entire IF band of 4 – 8 GHz.
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4.
  • Lapkin, Igor, 1963, et al. (författare)
  • Optics Design and Verification for the APEX Swedish Heterodyne Facility Instrument (SHeFI)
  • 2008
  • Ingår i: In Proceedings of The 19th International Symposium on Space Terahertz Technology, Groningen, 28-30 April, 2008, ed. W. Wild, Space Research Organization of the Netherlands (SRON). ; Part I, s. 351-357
  • Konferensbidrag (refereegranskat)abstract
    • We present the design and verification of the receiver optics for the Single-Pixel HeterodyneFacility Instrument (SHFI) of the APEX telescope [1]. The SHFI is designed to cover thefrequency band 211 – 1390 GHz in 6 receiver channels. Four of the receiver channels have beendesigned, installed and characterized: 211-275 GHz (Band 1); 275-370 GHz (Band 2); 385-500 GHz (Band 3); 1250-1390 GHz (Band T2). The first three bands employ 2SB SIS mixertechnology and Band T2 employs HEB mixers in a waveguide balanced mixer configuration.The entire optics design was driven by the receiver position in the telescope Nasmyth cabin“A” (Fig.1) and the aperture limit of Ø150 mm, introduced by the elevation encoder inside theNasmyth tube A. This layout and the telescope geometry (~ 6 m distance from the focal plane tothe Cabin A) lead us to choose a single-pixel configuration and required using intermediateoptics with long focal distances. The common optics path, coupling the receivers to theCassegrain sub-reflector, consists of the three offset ellipsoidal mirrors, M3, M6, M8s, and threeflat mirrors, F4, F5, and F7s. The combination M3 and M6 via flat F4, F5, creates a Gaussiantelescope, providing frequency-independent re-imaging of the antenna focal plane from theCassegrain cabin into the Nasmyth cabin A. Switching between channels is achieved by theprecision rotating of the active mirror M8s. The mirror M8s in combination with each channelactive mirror M10 provides re-imaging of the secondary onto the feed horn aperture of theselected channel. Such a configuration provides frequency independent illumination of thesecondary with the edge taper -12dB. The angular position of the flat mirrors F9 is adjustable andgives additional possibility of fine-tuning of the beam alignment from the common optics toevery receiver channels.Verification of the optical designthrough measurements is essential inorder to align the beams from thecryostat windows to the commonoptics to minimize loss in thequasioptical guiding system. In orderto verify the design of the cold optics(corrugated horn + M10) in terms ofGaussian beam parameters, a newwideband vector field measurementsystem was developed [2]. Vectorfield measurements were performedfor band 1, 2, and 3, and scalarmeasurements were employed for theTHz band.
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5.
  • Monje, Raquel, 1979, et al. (författare)
  • A 0.5 THz Sideband Separation SIS Mixer for APEX Telescope
  • 2008
  • Ingår i: In Proceedings of The 19th International Symposium on Space Terahertz Technology, Groningen, 28-30 April, 2008, ed. W. Wild, Space Research Organization of the Netherlands (SRON). ; Part II, s. 439-443
  • Konferensbidrag (refereegranskat)abstract
    • We present the design and the experimental results of a fixed-tuned sideband-separating superconductor-insulator-superconductor (SIS) mixer for 385 - 500 GHz. The sideband separation is achieved using a quadrature scheme, where two separate DSB mixer blocks are combined with an intermediate waveguide component containing the LO waveguide distribution circuitry and RF waveguide hybrid. The intermediate waveguide piece is fabricated by using copper micromachining, which gives dimensions’ accuracy better than 1 μm. The RF signal coming from the waveguide hybrid is coupled to the SIS junctions through an E-probe with integrated bias-T. We implemented an on-chip LO injection solution, where the LO coupler is integrated onto the mixer chip and fabricated together with the SIS junction and the tuning circuitry. The on-chip LO coupler is made as a combination of superconducting microstrip lines and slot-lines (branches), which gives almost a lossless solution. With the fabrication accuracy better than 0.5 μm by using optical lithography, the circuitry is proven to give a good performance following the simulations expectations.
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6.
  • Nyström, Olle, 1979, et al. (författare)
  • Low-Noise Cryogenic Amplifier built using Hybrid MMIC-like / TRL Technique
  • 2008
  • Ingår i: GigaHertz Symposium, March 5-6, 2008, Göteborg.
  • Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
    • HEMT cryogenic low-noise amplifiers are an important part of instrumentation: the amplifiersuse as a front-end for different measurements and as IF amplifiers in heterodyne receivers.During last few years the low-noise limit has reached as low level as approximately 0.5 K/GHzfor GaAs [1] and 0.25 K/GHz for InP HEMT [2]. However, besides electrical performanceimprovement there were not many improvements on mass and dimension side of suchamplifiers as they were built based on standard TRL technology with discrete active andpassive components. Mass and dimensions are also very important for real applications. Whenultimate low-noise performance is placed in focus, pure MMIC technology seems to looseagainst design using discrete components. With this in view, pioneered work by E. F. Lauria,et. al. [3] have successfully demonstrated a design employing MMIC approach while usingdiscrete components and based on a microstrip on Cuflon with lumped bias network.Encouraged by this work, we propose a compact design of a 4-8 GHz cryogenic low noiseamplifier using a combination of standard TRL and lumped element technology to achieveboth ultimate noise performance over the specified band and a very compact size. In ourdesign, the size reduction of the amplifier is realized by selecting an alumina substrate with ahigh dielectric constant, (εr = 9.9), but also by taking advantage of the lumped networks in thematching and bias circuitries. Avoiding quarter wave transformers and instead use a lumpedelement design approach opens up for the possibilities to reach greater bandwidths andsimultaneously obtain a more compact design. In order to make optimum design, we haveperformed extensive simulations. Each amplifier stage has been simulated in Agilent EMDS,3D electromagnetic field simulation package, including the single layer capacitors, and thenimplemented in the ADS circuit simulations as an S-parameter file. Over the 4-8 GHz band, thesimulations predict noise temperature, Taverage 35 dB. The transistors selected for the design are commercial InP HEMT (HRL) chosendue to their excellent noise performance [2], but also for the very low power consumption,which is of great importance at cryogenic temperatures. All the components used in the RFsignalpath and in the bias circuits are mounted with conductive epoxy. Apart from the RFsignalpath, all components are interconnected via bond-wires. Fine tuning is done by adjustingthe length and loop heights of the bond-wires. At the conference we plan to report results ofmeasurement and characterization of the prototype amplifier.REFERENCES:[1] C Risacher, et. al., “Low Noise and Low Power Consumption Cryogenic Amplifiers forOnsala and Apex Telescopes”, Proceedings of Gaas 2004, October 2004, Amsterdam.[2] N. Wadefalk, et. al., “Cryogenic Wide-Band Ultra-Low Noise IF Amplifier Operating atUltra-Low DC-Power”, IEEE Transactions on Microwave Theory and Techniques, vol. MTT-51, no. 6 June 2003.[3] E. F. Lauria, et. al., “A 200-300 GHz SIS Mixer-Preamplifier with 8 GHz IF Bandwidth”,2001 IEEE International Microwave Symposium, Phoenix, AZ, May 2001.
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7.
  • Nyström, Olle, 1979, et al. (författare)
  • Optics Design and Verificatgion for the APEX Swedish Heterodyne Facility Instrument (SHeFI)
  • 2009
  • Ingår i: Journal of Infrared, Millimeter, and Terahertz Waves. - : Springer Science and Business Media LLC. - 1866-6892 .- 1866-6906. ; 30:7, s. 746-761
  • Tidskriftsartikel (refereegranskat)abstract
    • In this paper, we present the design and verification of the optics of the Swedish Heterodyne Facility Instrument (SHeFI) receiver installed in the Atacama Pathfinder EXperiment (APEX) telescope during spring 2008. SHeFI is located in the Nasmyth instrumentation Cabin A (NCA). The receiver has been designed to have 6 frequency channels, of which four receiver channels have been built, and characterized: 211-275 GHz(Band 1), 275-370 GHz (Band 2), 385-500 GHz (Band 3), and 1250-1390 GHz (Band T2). Bands 1, 2, and T2 are installed at the telescope and are currently in operation. The optical design is driven by the requirement of frequency independent illumination of the secondary with -12 dB edge taper for each frequency channel and the limitation (beam clearance through the Nasmyth tube and the elevation encoder) imposed by the receiver position in the NCA. This paper describes the design approach, optimization, and verification of the optical system, coupling each individual receiving beam to the common optics of the telescope.
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8.
  • Vassilev, Vessen, 1969, et al. (författare)
  • A 211-275 GHz Sideband Separating SIS Mixer for APEX
  • 2007
  • Ingår i: Proceedings of the 17th International Symposium on Space Terahertz Technology, 10-12 May 2006, Paris, Edited by Dr. Alain Maestrini and Dr. Gérard Beaudin. ; , s. 145-148
  • Konferensbidrag (refereegranskat)abstract
    • We present the results of the development and characterization of the sideband separating (2SB) SIS mixer for the APEX band 1, 211-275 GHz.All mixer components, except the IF hybrid, are integrated into a single mixer block. The sideband separation is achieved by using a quadrature scheme where a local oscillator (LO) pumps two identical SIS mixers. The RF power is divided using a waveguide branch line coupler and directed with 900 phase difference to the ends of the substrate, where each path is coupled to the mixer chip through a waveguide to microstrip transition. Preliminary tests of this 2SB mixer show a sideband suppression ratio of about 12 dB and a typical SSB noise temperature of 80K.
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9.
  • Vassilev, Vessen, 1969, et al. (författare)
  • A Swedish heterodyne facility instrument for the APEX telescope
  • 2008
  • Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 490:3, s. 1157-1163
  • Tidskriftsartikel (refereegranskat)abstract
    • In March 2008, the APEX facility instrument was installed on the telescope at the site of Lliano Chajnantor in northern Chile. The main objective of the paper is to introduce the new instrument to the radio astronomical community. It describes the hardware configuration and presents some initial results from the on-sky commissioning.The heterodyne instrument covers frequencies between 211 GHz and 1390 GHz divided into four bands. The first threebands are sideband-separating mixers operating in a single sideband mode and based on superconductor-insulator-superconductor (SIS) tunnel junctions. The fourth band is a hot-electron bolometer, waveguide balanced mixer. All bands are integrated in a closedcycle temperature-stabilized cryostat and are cooled to 4 K.We present results from noise temperature, sideband separation ratios, beam, and stability measurements performed on the telescope as a part of the receiver technical commissioning. Examples of broad extragalactic lines are also included.
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  • Resultat 1-9 av 9

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