Jader Monari

Antenna Pattern Verification System Based on a Micro Unmanned Aerial Vehicle (UAV)

This letter presents a radiation pattern verification system for low-frequency antennas in their operative conditions, e.g., on the ground, next to other elements, etc. It is a far-field setup using a properly equipped micro unmanned aerial vehicle (UAV) as a test source. The micro UAV can perform an autonomous flight. Its absolute position is measured with a remote topographic instrument. By data processing, the received power pattern along the UAV flying path is reconstructed. The proposed setup has been validated on two standard wire antennas at 150 and 408 MHz with an estimated accuracy of 1 dB.

The Sky Polarization Observatory

Abstract The Sky Polarization Observatory (SPOrt) is an ASI-funded experiment specifically designed to measure the sky polarization at 22, 32 and 90 GHz, which was selected in 1997 by ESA to be flown on the International Space Station. Starting in 2006 and for at least 18 months, it will be taking direct and simultaneous measurements of the Stokes parameters Q and U at 660 sky pixels, with FWHM=7°. Due to development efforts over the past few years, the design specifications have been significantly improved with respect to the first proposal. Here we present an up-to-date description of the instrument, which now warrants a pixel sensitivity of 1.7 μK for the polarization of the cosmic background radiation, assuming two years of observations. We discuss SPOrt scientific goals in the light of WMAP results, in particular in connection with the emerging double-reionization cosmological scenario.

Status of the Sardinia Radio Telescope project

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.

Low frequency aperture array developments for phase 1 SKA

Aperture Arrays (AA) mark a new era in radio astronomy combining high sensitivity with a large field-of-view, enabling very high survey and imaging speeds. This paper describes the development of low frequency aperture arrays leading up to SKA phase 1 within the Aperture Array Verification Program (AAVP) as part of the SKA program.

Limits due to instrumental polarisation in CMB experiments at microwave wavelengths

Abstract An extended analysis of some instrumental polarisation sources has been done, as a consequence of the renewed interest in extremely sensitive polarisation measurements stimulated by Cosmic Microwave Background experiments. The case of correlation polarimeters, being them more suitable than other configurations, has been studied in detail and the algorithm has been derived to calculate their intrinsic sensitivity limit due to device characteristics as well as to the operating environment. The atmosphere emission, even though totally unpolarised, has been recognised to be the most important source of sensitivity degradation for ground based experiments. This happens through receiver component losses (mainly in the OMT), which generate instrumental polarisation in genuinely uncorrelated signals. The relevant result is that, also in best conditions (cfr. Antarctica), integration times longer than ∼40 s are not allowed on ground without modulation techniques. Finally, basic rules to estimate the maximum modulation period for each instrumental configuration have been provided.

From MAD to SAD: The Italian experience for the Low Frequency Aperture Array of SKA1‐LOW

This paper describes two small aperture array demonstrators called Medicina and Sardinia Array Demonstrators (MAD and SAD, respectively). The objectives of these instruments are to acquire experience and test new technologies for a possible application to the low-frequency aperture array of the low-frequency telescope of the Square Kilometer Array phase 1 (SKA1-LOW). The MAD experience was concluded in 2014, and it turned out to be an important test bench for implementing calibration techniques based on an artificial source mounted in an aerial vehicle. SAD is based on 128 dual-polarized Vivaldi antennas and is 1 order of magnitude larger than MAD. The architecture and the station size of SAD, which is along the construction phase, are more similar to those under evaluation for SKA1-LOW, and therefore, SAD is expected to provide useful hints for SKA1-LOW.

UAV-based pattern measurement of the SKALA

A novel antenna pattern measurement technique has been recently developed exploiting the capabilities of a micro Unmanned Aerial Vehicle (UAV) as a far-field test-source. This technique is suitable for characterizing VHF antennas such as those for low-frequency radio astronomy. This paper presents some of the measurements recently performed on the Square Kilometer Array Log-periodic Antenna (SKALA), which has been selected as the receiving element for the Low Frequency Aperture Array (LFAA).

UAV-based radiation pattern verification for a small low-frequency array

The Unmanned Aerial Vehicle (UAV) technology has been recently used to develop a pattern measurement system for low-frequency arrays in their real installation conditions. This paper presents the most important results that have been obtained on the Italian Medicina Array Demonstrator (MAD).

Antenna pattern characterization of the low-frequency receptor of LOFAR by means of an UAV-mounted artificial test source

Low frequency aperture array technology requires advanced ad-hoc tools for performing antenna and array pattern characterization and instrumental calibration. A micro Unmanned Aerial Vehicle (UAV) mounting a radio-frequency transmitting system developed in Italy has demonstrated to satisfy the challenging characteristics of these tasks. Therefore, a measurement campaign by means of this UAV system has been planned to one Dutch station of the Low Frequency Array (LOFAR) with the main goal to improve the LOFAR antenna and array models. In preparation for this campaign, some initial tests applying the UAV system to one low-frequency antenna of LOFAR were performed in Italy. This contribution describes this measurement session and shows that the measured antenna gain patterns at different frequencies between 40 and 70 MHz agree very well with the electromagnetic models.

On-board calibration system for millimeter-wave radiometers based on reference-polarized signal injection

This paper presents the architecture of a novel on-board calibration system for millimeter-wave radiometers aimed at measuring the Q,U Stokes parameters of the sky emission. This technique requires the injection of differently polarized reference signals, which is carried out by means of a specific component mounted in the antenna-feed system. The presented technique was developed by Cortiglioni et al. for the calibration of the Balloon-borne Radiometers for Sky Polarization Observations radiometers, specifically designed to measure the polarized sky emission by a correlation technique. A procedure for the accurate evaluation of the polarization state of the calibration signals is also reported. Numerical and experimental results are presented for the Ka-band calibrator in the operational conditions