Space debris is becoming a very important and urgent problem for present and future space activities. For that reason many public and private Institutions in the world are being involved in order to monitor and control the debris population increase and to understand which facilities can be used for improving the surveillance and tracking capabilities. In this framework in 2014 we performed some preliminary observations in a beam parking, CW mode and a bistatic configuration, with a transmitter of 4 kW of the Italian Air Force and the SRT (Sardinia Radio Telescope) a 64 meters radiotelescope used as a receiver. We performed the observations in P band at 410 MHz, receiving the signal diffused from some debris of different sizes and distances in LEO orbit, in order to understand the performances and capabilities of the system. In this article we will describe the results of this observations campaign, the simulation work done for preparing it, the RCS (radar cross section) observed, the level of the received signals, the Doppler measurements, and the work we are doing for developing a new and higher performing digital back end, able to process the data received.
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.
Existing radio receivers have a very low noise temperature. To further increase the observation speed, the new generation
of radio receivers use a multi-beam focal plane array (FPA) together with wide bandwidth. In this article, we present the
front-end and cryogenic design of the 7-beam FPA double linear polarization receiver for the 64-m primary focus of the
Sardinia Radio Telescope. At the end of this article, we show the simulated performances of the front-end receiver and
the measurements of the down-conversion section.
Proc. SPIE. 9914, Millimeter, Submillimeter, and Far-Infrared Detectors and Instrumentation for Astronomy VIII
KEYWORDS: Principal component analysis, Zinc, Fourier transforms, Interference (communication), Field programmable gate arrays, Space telescopes, Signal processing, Galactic astronomy, Signal detection, Stochastic processes
SETI, the Search for ExtraTerrestrial Intelligence, is the search for radio signals emitted by alien civilizations living in the Galaxy. Narrow-band FFT-based approaches have been preferred in SETI, since their computation time only grows like N*lnN, where N is the number of time samples. On the contrary, a wide-band approach based on the Kahrunen-Lo`eve Transform (KLT) algorithm would be preferable, but it would scale like N*N. In this paper, we describe a hardware-software infrastructure based on FPGA boards and GPU-based PCs that circumvents this computation-time problem allowing for a real-time KLT.
We present the control system of the 84-116 GHz (3 mm band) Superconductor-Insulator-Superconductor (SIS)
heterodyne receiver to be installed at the Gregorian focus of the Sardinia Radio Telescope (SRT). The control system is
based on a single-board computer from Raspberry, on microcontrollers from Arduino, and on a Python program for
communication between the receiver and the SRT antenna control software, which remotely controls the backshorttuned
SIS mixer, the receiver calibration system and the Local Oscillator (LO) system.
The noise temperature of existing radio telescope receivers has actually achieved very low values. In any case, there are other practical ways to increase the observational speed of a single dish antennas without using longer integration time: observe with multi-beam and large bandwidth receiver. In this paper we present the front end and the cryogenic dewar design of the 5 beams FPA double linear polarization receiver for the primary focus of the 64 m Sardinia Radio Telescope.
We present the optical and mechanical design of a 3mm band SIS receiver for the Gregorian focus of the Sardinia Radio Telescope (SRT). The receiver, was designed and built at IRAM and deployed on the IRAM for the Plateau de Bure Interferometer antennas until 2006. Following its decommissioning the receiver was purchased by the INAFAstronomical Observatory of Cagliari with the aim to adapt its optics for test of the performance of the new 64-m diameter Sardinia Radio Telescope (SRT) in the 3 mm band (84 – 116 GHz). The instrument will be installed in the rotating turret inside of the Gregorian focal room of SRT. The dimensions of the focal room, the horn position in the lower side of the cryostat and the vessel for the liquid helium impose very hard constraints to the optical and mechanical mounting structure of the receiver inside the cabin. We present the receiver configuration and how we plan to install it on SRT.
The Sardinia Radio Telescope (SRT) Metrology team has started to install the initial group of devices on the new 64 meters radio-telescope. These devices will be devoted for the realization of the antenna deformation control system: an electronic inclinometer able to monitor the alidade deformations and a Position Sensing Device (PSD) able to map the secondary mirror (M2) displacements and tilts. The inclinometer is used to map the rail conditions, the azimuthal axis inclination and the thermal effects on the alidade structure. The PSD will be used to measure the secondary mirror displacements induced by the gravity and by the thermal deformations that produce shifts and tilts with respect to it s ideal optical alignment. The PSD will be traced by a laser diode installed on a mechanically stable position inside the vertex room. Preliminarly we decided to characterize excursion range of M2, in order to know if the PSD measuring range of about +/- 10 mm is enough for our purposes. We designed, built and tested an optical measuring device, based on commercial CMOS with a wider measurement range of +/- 40 mm and with a resolution of around 0.1 mm. After a laboratory characterization at the 23 meters real distance, the PSD and the laser have been installed in the antenna. In this paper we show the results of the measurements performed by moving the antenna in elevation.
Here we present the hardware and software of the inclinometer chosen to be installed on the SRT alidade. This is a commercial device which basically uses two pendulum-like sensors to measure two angles from which the antenna pointing errors can be easily inferred. Such an inclinometer was installed on the plane of the SRT alidade close to the antenna elevation axis to measure the azimuth and elevation axis tilts due to the not-perfect flatness of the rail and to the temperature gradient effects on the alidade steel beams. Last summer some tests were carried out during night time, allowing first to check the inclinometer in a measurement set-up aboard on SRT, and then, to monitor the axis tilt due mainly to the rail roughness. Several measurements were recorded by the inclinometer, while the antenna was moving at constant speed in the azimuth direction for a 360-degrees rotation. The results showed a good agreement with those we got during the laboratory tests, and the rail turned out to be plan within the expected accuracy, which means a resulting pointing error of about ±2 arc-sec. Finally inclinometer measurements and astronomical observations have been performed all at once. The inclinometer measurements and the antenna pointing offsets due mainly to thermal effects have been recorded, while SRT was observing at 23 GHz toward a circumpolar calibrator source for many hours after the sunrise. A good agreement between the two set of measurement has been found as will be shown here following.
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 downconverted to baseband. 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
The Sardinia Radio Telescope (SRT) Metrology team is planning to install an initial group of devices on the new 64
meters radio-telescope. These devices will be devoted for the realization of the antenna deformation control system: an
electronic inclinometer able to monitor the alidade deformations and a Position Sensing Device (PSD) able to map the
antenna secondary mirror (M2) displacements and tilts. The inclinometer will be used to map the rail conditions, the
azimuthal axis inclination and the thermal effects on the alidade structure. The PSD will be used to measure the
secondary mirror displacements induced by the gravity and by the thermal deformations that produce shifts and tilts with
respect to its ideal optical alignment. The PSD will be traced by diode laser installed on a mechanically stable position
inside the elevation equipment room. The inclinometer has been tested in laboratory with the aim to compare its
performances with a reference measurement system. The PSD and the laser have been characterized by a long-term tests
to assess their stability and accuracy, thus simulating the open air conditions that will be experienced by the device
during its operative life. M2 may move freely in space thanks to a six axis actuator system (hexapod). The PSD
measurements are processed by a hexapod kinematic model (HKM) to evaluate the correct actuator elongations, thus
closing the control loop. The sensors will be acquired and recorded by a dedicated PC installed in the Alidade equipment
room and connected to the sensors via the Ethernet network.
We present here the systems aimed to measure and minimize the pointing errors for the Sardinia Radio Telescope: they
consist of an optical telescope to measure errors due to the mechanical structure deformations and a lasers system for the
errors due to the subreflector displacement. We show here the results of the tests that we have done on the Medicina 32
meters VLBI radio telescope. The measurements demonstrate we can measure the pointing errors of the mechanical
structure, with an accuracy of about ~1 arcsec. Moreover, we show the technique to measure the displacement of the
subreflector, placed in the SRT at 22 meters from the main mirror, within ±0.1 mm from its optimal position. These
measurements show that we can obtain the needed accuracy to correct also the non repeatable pointing errors, which
arise on time scale varying from seconds to minutes.
We studied the thermal effects on the 32 m diameter radio-telescope managed by the Institute of Radio Astronomy
(IRA), Medicina, Bologna, Italy. The preliminary results show that thermal gradients deteriorate the pointing
performance of the antenna.
Data has been collected by using: a) two inclinometers mounted near the elevation bearing and on the central part of the
alidade structure; b) a non contact laser alignment optical system capable of measuring the secondary mirror position; c)
twenty thermal sensors mounted on the alidade trusses.
Two series of measurements were made, the first series was performed by placing the antenna in stow position, the
second series was performed while tracking a circumpolar astronomical source.
When the antenna was in stow position we observed a strong correlation between the inclinometer measurements and the
differential temperature. The latter was measured with the sensors located on the South and North sides of the alidade,
thus indicating that the inclinometers track well the thermal deformation of the alidade.
When the antenna pointed at the source we measured: pointing errors, the inclination of the alidade, the temperature of
the alidade components and the subreflector position. The pointing errors measured on-source were 15-20 arcsec greater
than those measured with the inclinometer.
The Sardinia Radio Telescope (SRT) is a 64 meters (diameter) single dish radioantenna which is in the building phase in
Italy. One of the most challenging characteristics of SRT is its capability to observe up to a frequency of 100 GHz thanks
to its main reflector active surface. The active surface is composed by 1008 panels and 1116 mechanical actuators which
may modify the segmented shape of the main reflector making possible the correction for wavefront distortions induced
by the gravitational and thermal deformations.
In order to observe at a frequency of 100 GHz the surface shape must be accurate below of a value of 150 μm r.m.s..
This value may be reached during the initial alignement phase using the microwave holography but it cannot be
maintained during the scientific operations because of the (dynamical) deformations. In order to permit the observations
at any time, a system able to measure the surface deformations with the necessary accuracy and a time-response of few
minutes (the time-scale of the deformations) must be operative.
We propose here three simple and robust methods to measure the relative deformations of the segmented panels with
respect to an initial aligned surface (reference surface). The ultimate choice on which one of the three systems will
operate on SRT will be taken after final testing on all of them. Prototypes of each system have been realized and two of
them have been also successfully tested on the active optics radiotelescope of Noto (Italy). The test on the third system
will be done in the next few months.
We describe the design construction and performance of a L-band (1300-1800 MHz) Ortho Mode Junction for the L-P
dual-band receiver to be installed on the 64 m Sardinia Radio Telescope (SRT), a new radio telescope which is being
built in Sardinia, Italy. The Ortho Mode Junction (OMJ) separates two orthogonal linearly polarized signals propagating
in a 172 mm diameter circular waveguide and couple them into four coaxial outputs. The OMJ is part of an OMT (Ortho
Mode Transducer), which includes two 180<sup>0</sup> hybrids allowing to recombine the out-of-phase signals from the balanced
OMJ outputs. The OMJ consists of four probes arranged in symmetrical configuration across the circular waveguide. A
shaped tuning stub with cylindrical profile is placed a quarter wavelength away from the probes to guarantee broadband
operation with low reflection coefficient across L-band. The four identical probes have a cylindrical structure, each
consisting of three concentric cylinders that attach to the central pin of standard 50 Ω 7/16-type coaxial connectors. The
OMJ will be cooled at 80 K inside a compact dewar together with directional couplers and Low Noise Amplifiers.
The two linearly polarized signals from an input 190 mm diameter room temperature L-band feed couple into the
cryogenic dewar through a vacuum window located across the waveguide. Inside the dewar, the 190 mm diameter
circular waveguide is tapered down to 172 mm using a conical transition (length 85 mm) filled with a Styrodur® foam
that provides mechanical support for a 0.125 mm thick Kapton vacuum barrier. A 0.6 mm air gap across the 172 mm
circular waveguide provides thermal decoupling between the ambient temperature and the 80 K OMJ, which is
connected to the conical transition output.
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 describe the design, construction and performance of a novel 180° hybrid power divider for L-band (1.3-1.8 GHz).
The hybrid is based on a double ridged waveguide cavity that also integrates a band pass filter. The device will operate at
77 K inside a cryogenically cooled receiver to be installed at the primary focus of the Sardinia Radio Telescope.
The hybrid has three ports consisting of N-type coaxial connectors whose central pins are attached to launching probes
located inside the double ridge waveguide structure. The signal is launched into the cavity from an input probe located
on one cavity end and is extracted from two output probes on the opposite end. The output probes are arranged in
balanced configuration, are axially symmetric, and aligned along the same axis. Both input and output probes are located
in front of reactive loads consisting of shaped tunerless backshorts that provide broad band responses with low reflection
The band pass filter is located in the middle of the cavity, between the two input and output transitions. The dimensions
of the device (excluding connectors) are 70 x 57.2 x 254.4 mm<sup>3</sup>.
The design was optimized using a commercial electromagnetic simulator.
From 1.3-1.8 GHz the measured output reflection coefficient was less than -17dB , the coupling and the phase difference
between inputs and output was respectively, 3±0.25dB and 180<sup>0</sup>±0.9<sup>0</sup>, over the full band. The amplitude and phase
balance performances are much superior to that of commercially available devices.
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.
We describe the design, construction, and characterization results of a compact L-band (1.3-1.8 GHz) Orthomode
Transducer (OMT) for the Sardinia Radio Telescope (SRT), a 64 m diameter telescope which is being built in the
Sardinia island, Italy. The OMT consists of three distinct mechanical parts connected through ultra low loss coaxial
cables: a turnstile junction and two identical 180° hybrid power combiners. The turnstile junction is based on a circular
waveguide input (diameter of 190 mm,) and on four WR650 rectangular waveguide cavities from which the RF signals
are extracted using coaxial probes. The OMT was optimized using a commercial 3D electromagnetic simulator. The
main mechanical part of the turnstile junction was machined out of an Aluminum block whose final external shape is a
cylinder with diameter 450 mm and height 98 mm.
From 1.3 to 1.8 GHz the measured reflection coefficient was less than -22 dB, the isolation between the outputs was less
than -45 dB, and the cross polarization was less than -50 dB for both polarization channels.