In this article, we present the design and performances of the radio receiver system installed at the Sardinia Radio
Telescope (SRT). The three radio receivers planned for the first light of the Sardinian Telescope have been installed in
three of the four possible focus positions. A dual linear polarization coaxial receiver that covers two frequency bands,
the P-band (305-410 MHz) and the L-band (1.3-1.8 GHz) is installed at the primary focus. A mono-feed that covers the
High C-band (5.7-7.7 GHz) is installed at the beam waveguide foci. A multi-beam (seven beams) K-band receiver (18-
26.5 GHz) is installed at the Gregorian focus. Finally, we give an overview about the radio receivers, which under test
and under construction and which are needed for expanding the telescope observing capabilities.
ECCOSORB<sup>TM</sup> CR/MF is a widely used absorber at radio and millimeter wavelengths. It is used both at room and at cryogenic temperature to realize loads and calibrators both for laboratory and for space-borne instruments. Data on its RF properties are available from the data sheet at room temperature. But it is also widely used outside the design wavelength range and at cryogenic temperature, where specific measurement of electromagnetic and thermal properties are needed. Scarce information is available in the literature and inconsistencies are frequent. We report here new RF data in Ka and W-band at room temperature obtained with waveguide measurements with different setups.
We present the results of a development activity for cryogenic Low Noise Amplifiers based on HEMT technology for ground based and space-borne application. We have developed and realized two LNA design in W band, based on m-HEMT technology. MMIC chips have been manufactured by European laboratories and companies and assembled in test modules by our team. We compare performances with other technologies and manufacturers. LNA RF properties (noise figures, S-parameters) have been measured at room and cryogenic temperature and test results are reported in this paper. Performance are compared with those of state-of-the-art devices, as available in the literature. Strengths and improvements of this project are also discussed.
The Low Noise technology has a paramount relevance on radiotelescopes and radiometers performances. Its influence on
sensitivity and temporal stability has a deep impact on obtainable scientific results. As well known, front end active part
of scientific instruments are cryocooled in order to drastically reduce the intrinsic thermal noise generated by its
electronic parts and consequently increase the sensitivity. In this paper we will describe the obtained results by an Italian
Space Agency funded activity. The aim is to validate European MMIC Low Noise technologies and designs for
cryogenic environments in the range of millimetre wave. As active device, HEMT (High Electron Mobility Transistor)
are considered the best device for high frequency and low noise cryo applications. But not all the semiconductor foundry
process are suitable for applications in such environment. Two European Foundries has been selected and two different
HEMT based Low Noise Amplifiers have been designed and produced. The main goal of this activity is identify an
European technology basement for space and ground based low noise cryogenic applications. Designs, layout,
architectures, foundry processes and results will be compared.
Cryogenic Low Noise Amplifiers, based on MMIC HEMT technology, require a careful packaging to reach optimal
performance. Differences between modeled and measured performance can often be related to chip mounting details. In
the framework of the development of new cryogenic LNAs, described in a companion paper, we have developed a
specific packaging to host W-band cryogenic MMIC LNAs. We present here some of the main factors analyzed in the
design and chip integration activities. In particular, mechanical and thermal modeling, LNA chip gluing and adhesive
properties, sensitivity to components integration accuracy (i.e. deviation from the ideal orientation). Preliminary test
results are also reported.
We present the design of the passive feed system of the dual-band receiver for the prime focus of the Sardinia Radio
Telescope (SRT), a new 64 m diameter radio telescope which is being built in Sardinia, Italy. The feed system operates
simultaneously in P-band (305-410 MHz) and L-band (1300-1800 MHz). The room temperature illuminators are
arranged in coaxial configuration with an inner circular waveguide for L-band (diameter of 19 cm) and an outer coaxial
waveguide for P-band (diameter of 65 cm). Choke flanges are used outside the coaxial section to improve the crosspolarization
performance and the back scattering of the P-band feed. The geometry was optimized for compactness and
high antenna efficiency in both bands using commercial electromagnetic simulators. Four probes arranged in
symmetrical configuration are used in both the P and the L-band feeds to extract dual-linearly polarized signals and to
combine them, through phased-matched coaxial cables, into 180 deg hybrid couplers. A vacuum vessel encloses the two
P-band hybrids and the two L-band hybrids which are cooled, respectively at 15 K and 77 K. For the P-Band, four low
loss coaxial feedthroughs are used to cross the vacuum vessel, while for the L-Band a very low loss large window is
employed. The P-band hybrids are based on a microstrip rat-race design with fractal geometry. The L-band hybrids are
based on an innovative double-ridged waveguide design that also integrates a band-pass filter for Radio Frequency
Interference (RFI) mitigation.
We present the status of the Sardinia Radio Telescope (SRT) project, a new general purpose, fully steerable 64 m
diameter parabolic radiotelescope capable to operate with high efficiency in the 0.3-116 GHz frequency range. The
instrument is the result of a scientific and technical collaboration among three Structures of the Italian National Institute
for Astrophysics (INAF): the Institute of Radio Astronomy of Bologna, the Cagliari Astronomy Observatory (in
Sardinia,) and the Arcetri Astrophysical Observatory in Florence. Funding agencies are the Italian Ministry of Education
and Scientific Research, the Sardinia Regional Government, and the Italian Space Agency (ASI,) that has recently
rejoined the project. The telescope site is about 35 km North of Cagliari.
The radio telescope has a shaped Gregorian optical configuration with a 7.9 m diameter secondary mirror and
supplementary Beam-WaveGuide (BWG) mirrors. With four possible focal positions (primary, Gregorian, and two
BWGs), SRT will be able to allocate up to 20 remotely controllable receivers. One of the most advanced technical
features of the SRT is the active surface: the primary mirror will be composed by 1008 panels supported by electromechanical
actuators digitally controlled to compensate for gravitational deformations. With the completion of the
foundation on spring 2006 the SRT project entered its final construction phase. This paper reports on the latest advances
on the SRT project.