F. Gaudiomonte

A Printed LPDA Fed by a Coplanar Waveguide for Broadband Applications

A printed log-periodic dipole array (LPDA), operating between 3 and 6 GHz and fed with a coplanar waveguide, is presented. The antenna has been designed starting from Carrels theory, optimized using CST Microwave Studio 2012, and then realized. The comparison between simulated and measured results shows that the proposed antenna can be used for broadband applications in the whole operating frequency band (3-6 GHz), with a very good input matching and a satisfactory endfire radiation pattern.

The microwave holography system for the Sardinia Radio Telescope

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 RMS.

Sardinia Array Demonstrator: Instrument overview and status

In the framework of the Square Kilometer Array (SKA) project, the Italian Institute for Astrophysics (INAF) has addressed several efforts in the design and prototyping of aperture arrays for low-frequency radio astronomical research. The Sardinia Array Demonstrator (SAD) is a national project aimed to develop know-how in this area and to test different architectural technologies and calibration algorithms. SAD consists of 128 prototypical dual-polarized Vivaldi antennas designed to operate at radio frequencies below 650 MHz. The antennas will be deployed at the Sardinia Radio Telescopes site with a versatile approach able to provide two different array configurations: (i) all antennas grouped in one large station or (ii) spread among a core plus few satellite stations. This paper provides an overview of the SAD project from an instrumental point of view, and illustrates its status after 2 years from its start.

Sardinia aperture array demonstrator

We present a project aimed at realizing an Italian aperture array demonstrator constituted by prototypical Vivaldi antennas designed to operate at radio frequencies below 500 MHz. We focus on an array composed of a core plus a few satellite phased-array stations to be installed at the Sardinia Radio Telescope (SRT) site. The antenna elements are mobile and thus it will be possible to investigate the performance in terms of both uv-coverage and synthesized resolution resulting from different configurations of the array.

The sardinia radio telescope: Overview and status

The Sardinia Radio Telescope is approaching to its official inauguration. Nowadays, the technical staff is accomplishing the last remaining activities to set up and integrate the microwave receivers, the digital processing systems and all the equipment necessary to reach a top level in the international scenario of large radio telescopes. Even if the radio telescope is still along the technical commissioning, SRT has already performed its first astronomical detection. This early scientific result opens exciting perspectives for the time when SRT will be in the full operational phase.

A multifeed S-band cryogenic receiver for the Sardinia Radio Telescope primary focus

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.

The Mobile Laboratory for Radio-Frequency Interference Monitoring at the Sardinia Radio Telescope

In this paper, a quite unique mobile laboratory for monitoring radio-frequency interference with a radio-astronomical observatory is described. The unit is fully operational at the new Sardinia Radio Telescope, a 64-m antenna now in the commissioning phase in Italy. The mobile laboratory is mainly used to identify the source of interference with the radio astronomy service using iterative triangulations in the azimuth directions. Both the design and realization of this prototype were handled with outstanding care to limit the emission of self-interference as much as possible. The laboratory was equipped with excellent microwave instruments in terms of sensitivity, frequency coverage, dynamic range, and various demodulation and signal-analysis facilities. The unit can be quickly switched to different RF and power-supply configurations, while offering operators a safe and efficient workplace, even in adverse meteorological and driving conditions. In the past months, the mobile laboratory has proven to be successful in detecting and identifying many radio interferers. Two examples of measurement campaigns are described.

Imaging of SNR IC443 and W44 with the Sardinia Radio Telescope at 1.5 and 7 GHz

Observations of supernova remnants (SNRs) are a powerful tool for investigating the later stages of stellar evolution, the properties of the ambient interstellar medium, and the physics of particle acceleration and shocks. For a fraction of SNRs, multi-wavelength coverage from radio to ultra high-energies has been provided, constraining their contributions to the production of Galactic cosmic rays. Although radio emission is the most common identifier of SNRs and a prime probe for refining models, high-resolution images at frequencies above 5 GHz are surprisingly lacking, even for bright and well-known SNRs such as IC443 and W44. In the frameworks of the Astronomical Validation and Early Science Program with the 64-m single-dish Sardinia Radio Telescope, we provided, for the first time, single-dish deep imaging at 7 GHz of the IC443 and W44 complexes coupled with spatially-resolved spectra in the 1.5-7 GHz frequency range. Our images were obtained through on-the-fly mapping techniques, providing antenna beam oversampling and resulting in accurate continuum flux density measurements. The integrated flux densities associated with IC443 are S_1.5GHz = 134 +/- 4 Jy and S_7GHz = 67 +/- 3 Jy. For W44, we measured total flux densities of S_1.5GHz = 214 +/- 6 Jy and S_7GHz = 94 +/- 4 Jy. Spectral index maps provide evidence of a wide physical parameter scatter among different SNR regions: a flat spectrum is observed from the brightest SNR regions at the shock, while steeper spectral indices (up to 0.7) are observed in fainter cooling regions, disentangling in this way different populations and spectra of radio/gamma-ray-emitting electrons in these SNRs.

The new time and Frequency laboratory for the Sardinia Radio Telescope

A time laboratory was established at the Astronomical Observatory of Cagliari more than one century ago, aimed for time-tagging scientific observations. At present, this laboratory is facing up a deep refurbishment in order to cope with the much tighter specifications on phase noise, time resolution, and frequency stability required by the new scientific applications planned for the Sardinia Radio Telescope. As a result of the participation to millimeter Very Long Baseline Interferometry and pulsar timing experiments of SRT, the new Time and Frequency laboratory will be called to provide extremely low phase noise and highly stable frequency references.

Commissioning of the Sardinia Radio Telescope in Italy: Results and perspectives

On 30 September 2013, the opening ceremony of SRT has signed the contractual ending of the instrumental commissioning of the Sardinia Radio Telescope. In February 2014 it has been completed also the “fine tuning process” aimed at defining the first optimizations parameters needed to make calibrated radio astronomical observations. Since then, the final Astronomical Validation, that was just started in parallel with the previous activities, has taken the lead of the users allocated time. At the time of the real presentation in August we expect to be able to present the experimental quantitative results of the commissioning that at the time of this writing are still under analysis.