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  • 1
    Electronic Resource
    Electronic Resource
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 1288-1292 
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We describe the design and construction of a filterbank of novel design which uses sections of coaxial transmission line as filter elements. This filterbank is a lower cost alternative to standard (solid-state) filterbank designs, and is appropriate in situations where large total bandwidths are required, as is the case for submillimeter observations of extragalactic objects.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-9559
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Conclusions A new type of optical filter element has been described and tested, offering an alternative frequency response to that of a Fabry-Perot or Michelson interferometer. It is quite compact, mechanically stable, and suitable for cryogenic operation. Use of this device is planned as a sideband filter in a 15 element imaging array receiver for 90–115 GHz.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1572-9559
    Keywords: water vapor spectroscopy ; submillimeter-wave radiometry ; heterodyne radiometer ; submillimeter-wave oscillator ; frequency multiplier
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract A compact, solid state submillimeter-wave heterodyne radiometer has been developed and was used to measure spectral characteristics of a water vapor jet in a space simulation chamber. Features of the 557 GHz water vapor line profile were observed in significantly greater detail than in previous experiments through an increased sensitivity and improved frequency resolution (600 kHz). The local oscillator of the radiometer consisted of a frequency multiplication chain which was driven by an InP Gunn oscillator at 92.6 GHz, and which contained a frequency tripler and harmonic mixer in cascade. The front end of the receiver had a noise temperature of 4500 K (DSB) at 555 GHz, consumed 3 W and weighed 3 kg. This advance in technology is particularly relevant to submillimeter-wave radiometry from a space-based platform.
    Type of Medium: Electronic Resource
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  • 4
    Publication Date: 2013-08-31
    Description: A new type of frequency multiplier structure is being developed which is suitable for application at frequencies above 1 THz. This structure preserves some of the properties of waveguide for mode control, yet is not truly single mode. The device resembles a sectoral horn, with a varactor diode mounted near the throat. Input and output coupling are through the same aperture, requiring a quasi-optical diplexer. Initial tests are directed at building a tripler at 500 GHz, for comparison with waveguide structures. The diplexer is a blazed diffraction grating with appropriate focusing optics. Model studies show that the impedance match to a varactor should be good, and initial tests of the beam patterns of the prototype indicate that optical coupling efficiency should be very high. The structure also has the potential for use as a fundamental mixer, or as a third harmonic mixer.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: Michigan Univ., The Third International Symposium on Space Terahertz Technology: Symposium Proceedings; p 181-188
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  • 5
    Publication Date: 2013-08-31
    Description: The efficiency of the Schottky diode multiplier can be increased by cooling the diode to 77 K. The main reason for better efficiency is the increased mobility of the free carriers. Because of that the series resistance decreases and a few dB higher efficiency can be expected at low input power levels. At high output frequencies and at high power levels, the current saturation decreases the efficiency of the multiplication. When the diode is cooled the maximum current of the diode increases and much more output power can be expected. There are also slight changes in the I-V characteristic and in the diode junction capacitance, but they have a negligible effect on the efficiency of the multiplier.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: Michigan Univ., The Third International Symposium on Space Terahertz Technology: Symposium Proceedings; p 134-145
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  • 6
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    In:  Other Sources
    Publication Date: 2011-08-19
    Description: A waveguide Schottky barrier diode mixer, which in preliminary tests has yielded a single sideband receiver noise temperature of 4300 K at 692 GHz, when cooled to 77 K is presented. Further refinements and operation at 20 K should produce a significant improvement in performance. From a system point of view, the very high efficiency of the radiation pattern produced by the conical feedhorn with cylindrical corrector mirror enhances the effective sensitivity by a factor of 1.5 to 2 compared to open-structure corner-reflector systems. A second-harmonic mixer for 557 GHz, also in the fundamental mode rectangular waveguide was developed. When combined with a frequency-tripled Gunn oscillator, this makes an extremely compact and lightweight submillimeter radiometer.
    Keywords: INSTRUMENTATION AND PHOTOGRAPHY
    Format: text
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  • 7
    Publication Date: 2019-07-10
    Description: We present spectral line profiles for the 557 GHz 1(sub 1,0) yields 1(sub 0,1) ground-state rotational transition of ortho-H2(16)O for 18 galactic star formation regions observed by SWAS. 2 Water is unambiguously detected in every source. The line profiles exhibit a wide variety of shapes, including single-peaked spectra and self-reversed profiles. We interpret these profiles using a Monte Carlo code to model the radiative transport. The observed variations in the line profiles can be explained by variations in the relative strengths of the bulk flow and small-scale turbulent motions within the clouds. Bulk flow (infall, outflow) must be present in some cloud cores, and in certain cases this bulk flow dominates the turbulent motions.
    Keywords: Astronomy
    Type: Preprint-Series-4900
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  • 8
    Publication Date: 2019-07-13
    Description: The goal of the UMass work on this grant was to build an LO source at 1036 GHz for a receiver which was to be built at JPL. The 1 THz source will consist of a high power Gunn oscillator at 86 GHz followed by a cascaded pair of planar diode doublers and finally a whisker contacted tripler. All multipliers will use single mode waveguide mounts. This use of single mode waveguide even for the final mount is a departure from the original plan, and reflects the progress that has been made in fabricating small structures. The advantages to the use of waveguide over a quasi-optical approach are that the complete system is much more compact, and much easier to use.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: NASA-CR-199560 , NAS 1.26:199560 , NIPS-95-05586
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  • 9
    Publication Date: 2019-07-13
    Description: Analysis of a planar diode multiplier from 85-170 GHz is described. The doubler uses a waveguide mount with two series pairs of diodes in a balanced structure. Because of the difficulties in conventional scale model measurements, numerical electromagnetic simulation based on the finite element method was chosen for the analysis, using a commercial program. To optimize the diode design, the de-embedded diode terminal impedance was studied, as well as the power balance between the diodes. The analysis showed that the matching of the diode impedance to that of the waveguide is quite sensitive to the diode substrate thickness. Thicknesses from 25-100 micron in GaAs were studied as well as 100-micron-thick quartz. The accuracy of the theoretical analysis was verified by careful measurements using a slotted line to determine the diode terminal impedance under large signal pump, for frequencies between 80 and 90 GHz. Good agreement between the measured and simulated diode terminal impedance was observed, although full agreement requires the addition of an empirical loss term. Several options are considered for the source of this loss.
    Keywords: ELECTRONICS AND ELECTRICAL ENGINEERING
    Type: International Symposium on Space Terahertz Technology. Part 2; May-94; Ann Arbor, MI; United States|IEEE Transactions on Microwave Theory and Techniques. Symp. on Space Terahertz Technology - May 1994 at the Univ. of Michigan, Ann Arbor. (ISSN 0018-9480); 43; 4, pt. 2; p. 962-968
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  • 10
    Publication Date: 2019-07-10
    Description: A long standing prediction of steady state gas-phase chemical theory is that H2O and O2 are important reservoirs of elemental oxygen and major coolants of the interstellar medium. Analysis of SWAS observations has set sensitive upper limits on the abundance Of O2 and has provided H2O abundances toward a variety of star forming regions. Based on these results, we show that gaseous H2O and O2 are not dominant carriers of elemental oxygen in molecular clouds. Instead the available oxygen is presumably frozen on dust grains in the form of molecular ices, with a significant portion potentially remaining in atomic form, along with CO, in the gas phase. H2O and O2 are also not significant coolants for quiescent molecular gas. In the case of H2O, a number of known chemical processes can locally elevate its abundance in regions with enhanced temperatures, such as warm regions surrounding young stars or in hot shocked gas. Thus, water can be a locally important coolant. The new information provided by SWAS, when combined with recent results from the Infrared Space Observatory, also provide several hard observational constraints for theoretical models of the chemistry in molecular clouds and we discuss various models that satisfy these conditions.
    Keywords: Astrophysics
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