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Cano J.L.,University of Cantabria | Wadefalk N.,Chalmers University of Technology | Gallego-Puyol J.D.,Centro Astronomico Of Yebes
IEEE Transactions on Microwave Theory and Techniques

A 20-dB chip attenuator designed for cryogenic noise measurements from dc up to 40 GHz is presented. The chip is based on the use of temperature-stable tantalumnitride thin-film resistors, a high thermal conductivity substrate such as crystal quartz (z-cut), and a suitable design that avoids inner conductor thermal heating, which is an important limiting factor for the precision of cryogenic noise measurements. A high-accuracy temperature sensor installed inside the attenuator module provides precise temperature characterization close to the chip location. The high thermal conductivity of the chip substrate in the designed attenuator assures a negligible temperature gradient between the resistive elements in the chip and the sensor, thus improving the measurement accuracy. The attenuator also shows an excellent electrical performance with insertion losses of 19.9 dB ± 0.65 dB and return losses better than 20.6 dB in the whole frequency range at 296 K. The insertion loss change when cooled to 15 K is less than 0.25 dB, which demonstrates its temperature stability. © 2010 IEEE. Source

Serra G.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Bolli P.,Istituto di Astrofisica Spaziale e Fisica Cosmica | Busonera G.,CRS4 | Pisanu T.,Istituto di Astrofisica Spaziale e Fisica Cosmica | And 6 more authors.
Proceedings of SPIE - The International Society for Optical Engineering

Microwave holography is a well-established technique for mapping surface errors of large reflector antennas, particularly those designed to operate at high frequencies. We present here a holography system based on the interferometric method for mapping the primary reflector surface of the Sardinia Radio Telescope (SRT). SRT is a new 64-m-diameter antenna located in Sardinia, Italy, equipped with an active surface and designed to operate up to 115 GHz. The system consists mainly of two radio frequency low-noise coherent channels, designed to receive Ku-band digital TV signals from geostationary satellites. Two commercial prime focus low-noise block converters are installed on the radio telescope under test and on a small reference antenna, respectively. Then the signals are amplified, filtered and down-converted to base-band. An innovative digital back-end based on FPGA technology has been implemented to digitize two 5 MHz-band signals and calculate their cross-correlation in real-time. This is carried out by using a 16-bit resolution ADCs and a FPGA reaching very large amplitude dynamic range and reducing post-processing time. The final holography data analysis is performed by CLIC data reduction software developed within the Institut de Radioastronomie Millimétrique (IRAM, Grenoble, France). The system was successfully tested during several holography measurement campaigns, recently performed at the Medicina 32-m radio telescope. Two 65-by-65 maps, using an on-the-fly raster scan with on-source phase calibration, were performed pointing the radio telescope at 38 degrees elevation towards EUTELSAT 7A satellite. The high SNR (greater than 60 dB) and the good phase stability led to get an accuracy on the surface error maps better than 150 μm RMS. © 2012 SPIE. Source

Ossenkopf V.,University of Cologne | Ossenkopf V.,SRON Netherlands Institute for Space Research | Rollig M.,University of Cologne | Simon R.,University of Cologne | And 39 more authors.
Astronomy and Astrophysics

Context. The molecular gas in the DR21 massive star formation region is known to be affected by the strong UV field from the central star cluster and by a fast outflow creating a bright shock. The relative contribution of both heating mechanisms is the matter of a long debate. Aims. By better sampling the excitation ladder of various tracers we provide a quantitative distinction between the different heating mechanisms. Methods. HIFI observations of mid-J transitions of CO and HCO+ isotopes allow us to bridge the gap in excitation energies between observations from the ground, characterizing the cooler gas, and existing ISO LWS spectra, constraining the properties of the hot gas. Comparing the detailed line profiles allows to identify the physical structure of the different components. Results. In spite of the known shock-excitation of H2 and the clearly visible strong outflow, we find that the emission of all lines up to ≳2 THz can be explained by purely radiative heating of the material. However, the new Herschel/HIFI observations reveal two types of excitation conditions. We find hot and dense clumps close to the central cluster, probably dynamically affected by the outflow, and a more widespread distribution of cooler, but nevertheless dense, molecular clumps. © 2010 ESO. Source

Munoz L.E.G.,Charles III University of Madrid | Lavado A.R.,Charles III University of Madrid | Aller M.M.,Charles III University of Madrid | Puente J.M.S.,Centro Astronomico Of Yebes | And 2 more authors.
2013 7th European Conference on Antennas and Propagation, EuCAP 2013

Two new topology that potentially can open new solutions for covering the new VLBI2010 configuration and its frequency bands associated are presented in this manuscript. In the first approach three bands are covered: 2.2-2.7 GHz, 7-9 GHz and 28-33 GHz. This new topology is based on an archimedean spiral on the top of two frequency selective surfaces (FSS's) and a ground plane. The architecture of the FSS's and their height to the antenna are optimized for covering the complete sub-bands. Second approach consider a single band from 2 to 14 GHz. A log-spiral printed on a semi-conic surface is place over a PEC ground plane. Whole structure is adjusted in order to obtain a pure circular polarization at broadside direction. © 2013 EurAAP. Source

Decin L.,Catholic University of Leuven | Decin L.,University of Amsterdam | Justtanont K.,Chalmers University of Technology | De Beck E.,Catholic University of Leuven | And 29 more authors.
Astronomy and Astrophysics

During their asymptotic giant branch evolution, low-mass stars lose a significant fraction of their mass through an intense wind, enriching the interstellar medium with products of nucleosynthesis. We observed the nearby oxygen-rich asymptotic giant branch star IK Tau using the high-resolution HIFI spectrometer onboard Herschel. We report on the first detection of H 216O and the rarer isotopologues H2 17O and H218O in both the ortho and para states. We deduce a total water content (relative to molecular hydrogen) of 6.6 × 10-5, and an ortho-to-para ratio of 3:1. These results are consistent with the formation of H2O in thermodynamical chemical equilibrium at photospheric temperatures, and does not require pulsationally induced non-equilibrium chemistry, vaporization of icy bodies or grain surface reactions. High-excitation lines of 12CO, 13CO, 28SiO, 29SiO, 30SiO, HCN, and SO have also been detected. From the observed line widths, the acceleration region in the inner wind zone can be characterized, and we show that the wind acceleration is slower than hitherto anticipated. © 2010 ESO. Source

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