Radio frequency over fiber technology for SKA-low receiver

The signal reception chain is an essential element for achieving the square kilometer array-low (SKA-low) system requirements in terms of high sensitivity and dynamic range. The balance between gain, linearity, and low power consumption, as well as the cost, are fundamental parameters that influence the selection of the most suitable technology for SKA-low. Further factors, such as low self-generated radio frequency (RF) interference, high reliability, robustness under extreme environment, and last but not least, the distance between the antennas and the acquisition systems, have impacts on the selection for both architecture and receiver system design. The selected technology for the SKA-low RF signal transportation is RF-over-fiber systems, where the preamplified RF signal picked up by the antennas is carried via analogue modulation over optical fiber. The rationales behind the selection are reported, along with descriptions on the development of the receiver prototypes. The prototypes were deployed and installed on the demonstrator arrays at the selected SKA-low site in Western Australian. Particular attention has been put on the thermal characterization of the receiver system under the actual operating temperature on site, especially when both transmitting part and the optical medium are subjected to external ambient temperature variations. Performance issues encountered in the demonstrator arrays are also discussed along with some proposals for future activities

Preliminary tests to design an ad hoc signal acquisition chain for the Sardinia Aperture Array Demonstrator

The Sardinia Aperture Array Demonstrator (SAD) is an Italian facility, which is composed of 128 prototypical Vivaldi antennas, specifically designed to operate across the 50-500 MHz frequency range. As well known, one of the major burden at low frequency are the radio frequency interferences, thus after several accurate measurement campaigns we realized that a specific signal conditioning is needed in order to feed the digital beamformer with the proper signal level. In this paper, we report the results of the preliminary tests that we carried out in order to design an ad hoc receiving chain for the SAD array

Combining multiple isotopes and metagenomic to delineate the role of tree canopy nitrification in European forests along nitrogen deposition and climate gradients

Forest canopies influence our climate through carbon, water and energy exchanges with the atmosphere. However, less investigated is whether and how tree canopies change the chemical composition of precipitation, with important implications on forest nutrient cycling. Recently, we provided for the first time isotopic evidence that biological nitrification in tree canopies was responsible for significant changes in the amount of nitrate from rainfall to throughfall across two UK forests at high nitrogen (N) deposition [1]. This finding strongly suggested that bacteria and/or Archaea species of the phyllosphere are responsible for transforming atmospheric N before it reaches the soil. Despite microbial epiphytes representing an important component of tree canopies, attention has been mostly directed to their role as pathogens, while we still do not know whether and how they affect nutrient cycling. Our study aims to 1) characterize microbial communities harboured in tree canopies for two of the most dominant species in Europe (Fagus sylvatica L. and Pinus sylvestris L.) using metagenomic techniques, 2) quantify the functional genes related to nitrification but also to denitrification and N fixation, and 3) estimate the contribution of NO3 derived from biological canopy nitrification vs. atmospheric NO3 input by using \u3b415N, \u3b418O and \u3b417O of NO3in forest water. We considered i) twelve sites included in the EU ICP long term intensive forest monitoring network, chosen along a climate and nitrogen deposition gradient, spanning from Fennoscandia to the Mediterranean and ii) a manipulation experiment where N mist treatments were carried out either to the soil or over tree canopies. We will present preliminary results regarding microbial diversity in the phyllosphere, water (rainfall and throughfall) and soil samples over the gradient. Furthermore, we will report differences between the two investigated tree species for the phyllosphere core microbiome in terms of relative abundance of bacterial and Archaea classes and those species related to N cycling. Finally we will assess whether there are differences among tree species and sites in the number of functional genes related to N cycling and how they are related to the N deposition and/or climate. [1] Guerrieri et al. 2015 Global Change and Biology 21 (12): 4613-4626

Procedura di montaggio del sistema di movimentazione e controllo del ramo N/S per il sistema BIRALES

Lo scopo di questo documento è quello di descrivere la procedura dell’installazione del nuovo sistema di movimentazione delle antenne cilindrico paraboliche del ramo Nord/Sud del radiotelescopio “Croce del Nord”, studiato per venire incontro alle esigenze del programma “Space Surveillance and Tracking”, oltre a programmi scientifici quale la ricerca degli FRB. Oltre alla procedura di installazione, è indicata la lista del materiale necessario alla replicazione e i disegni costruttivi, e viene inoltre descritta la procedura di manutenzione

The Northern Cross Fast Radio Burst project -- III. The FRB-magnetar connection in a sample of nearby galaxies

Fast radio bursts (FRBs) are millisecond radio transients observed at cosmological distances. The nature of their progenitors is still a matter of debate, although magnetars are invoked by most models. The proposed FRB-magnetar connection was strengthened by the discovery of an FRB-like event from the Galactic magnetar SGR J1935+2154. In this work, we aim to investigate how prevalent magnetars such as SGR J1935+2154 are within FRB progenitors. We carried out an FRB search in a sample of seven nearby (< 12 Mpc) galaxies with the Northern Cross radio telescope for a total of 692 h. We detected one 1.8 ms burst in the direction of M101 with a fluence of $58 \pm 5$ Jy ms. Its dispersion measure of 303 pc cm$^{-3}$ places it most-likely beyond M101. Considering that no significant detection comes indisputably from the selected galaxies, we place a 38 yr$^{-1}$ upper limit on the total burst rate (i.e. including the whole sample) at the 95\% confidence level. This upper limit constrains the event rate per magnetar $\lambda_{\rm mag} < 0.42$ magnetar$^{-1}$ yr$^{-1}$ or, if combined with literature observations of a similar sample of nearby galaxies, it yields a joint constraint of $\lambda_{\rm mag} < 0.25$ magnetar$^{-1}$ yr$^{-1}$. We also provide the first constraints on the expected rate of FRBs hypothetically originating from ultraluminous X-ray (ULX) sources, since some of the galaxies observed during our observational campaign host confirmed ULXs. We obtain $< 13$ yr$^{-1}$ per ULX for the total sample of galaxies observed. Our results indicate that bursts with energies $E>10^{34}$ erg from magnetars like SGR J1935+2154 appear more rarely compared to previous observations and further disfavour them as unique progenitors for the cosmological FRB population, leaving more space open to the contribution from a population of more exotic magnetars, not born via core-collapsed supernovae.Comment: 9 pages, 4 figures, published in A&

Towards coordinated site monitoring and common strategies for mitigation of Radio Frequency Interference at the Italian radio telescopes

We present a project to implement a national common strategy for the mitigation of the steadily deteriorating Radio Frequency Interference (RFI) situation at the Italian radio telescopes. The project involves the Medicina, Noto, and Sardinia dish antennas and comprised the definition of a coordinated plan for site monitoring as well as the implementation of state-of-the-art hardware and software tools for RFI mitigation. Coordinated monitoring of frequency bands up to 40 GHz has been performed by means of continuous observations and dedicated measurement campaigns with fixed stations and mobile laboratories. Measurements were executed on the frequency bands allocated to the radio astronomy and space research service for shared or exclusive use and on the wider ones employed by the current and under-development receivers at the telescopes. Results of the monitoring campaigns provide a reference scenario useful to evaluate the evolution of the interference situation at the telescopes sites and a case series to test and improve the hardware and software tools we conceived to counteract radio frequency interference. We developed a multi-purpose digital backend for high spectral and time resolution observations over large bandwidths. Observational results demonstrate that the spectrometer robustness and sensitivity enable the efficient detection and analysis of interfering signals in radio astronomical data. A prototype off-line software tool for interference detection and flagging has been also implemented. This package is capable to handle the huge amount of data delivered by the most modern instrumentation on board of the Italian radio telecsopes, like dense focal plane arrays, and its modularity easen the integration of new algorithms and the re-usability in different contexts or telescopes.Comment: 39 pages, 10 Figures and 7 Tables. INAF Technical Report n. 149 (2022). http://hdl.handle.net/20.500.12386/3208

Developments of FPGA-based digital back-ends for low frequency antenna arrays at Medicina radio telescopes

In radio astronomy Field Programmable Gate Array (FPGA) technology is largely used for the implementation of digital signal processing techniques applied to antenna arrays. This is mainly due to the good trade-off among computing resources, power consumption and cost offered by FPGA chip compared to other technologies like ASIC, GPU and CPU. In the last years several digital backend systems based on such devices have been developed at the Medicina radio astronomical station (INAF-IRA, Bologna, Italy). Instruments like FX correlator, direct imager, beamformer, multi-beam system have been successfully designed and realized on CASPER (Collaboration for Astronomy Signal Processing and Electronics Research, https://casper.berkeley.edu) processing boards. In this paper we present the gained experience in this kind of applications

Test-Driven Design of an Active Dual-Polarized Log-Periodic Antenna for the Square Kilometre Array

An active dual-polarized Log-Periodic antenna has been designed to meet the requirements of the low-frequency (50-350 MHz) radio telescope of the Square Kilometre Array (SKA). The integration of antenna and low noise amplifier has been conceived in order to achieve a high degree of testability. This aspect has been found to be crucial to obtain a smooth frequency response compatible with the SKA science cases. The design has also been driven by other factors such as the large-volume production (more than 130 000 antennas will be built) and the environmental conditions of the harsh Australian desert. A specific verification approach based on both wideband radiometric spectral and spatial measurements in relevant laboratory and in-situ conditions has been developed. Electromagnetic analyses and experimental results exhibit a very good agreement. In December 2019, this antenna was part of the reference solution for the System Critical Design Review of the SKA

The UAV-based test source as an end-to-end verification tool for aperture arrays

A UAV-mounted radio-frequency transmitter is proposed as a known reference field source to perform a set of functional tests on aperture arrays. The experimental results obtained on complete prototypes (end-to-end) and sub-assemblies provide good confidence on both amplitude and timing verification

Exploration of an innovative ranging method for bi-static radar, applied in LEO Space Debris surveying and tracking

Space Situational Awareness (SSA) is referred as one of the capacitive areas of strategic interest to be developed/completed in the future in the short and medium term, for any nation with the target of the access to the space. One of the fundamental components is the Space Surveillance and Tracking (SST) program, considered as the capability to build a spatial mapping of the objects in orbit, their classification and the exact identification of their orbital characteristics. For this reason, radar measurements are relevant, in particular to observe objects in Low Earth Orbit. The Italian National Institute of Astrophysics together with Vitrociset company and Politecnico di Milano, studied and developed a new and innovative method for the range measure applied to bi-static radars to support the European Union Space Surveillance and Tracking (EUSST) program. Several tests have been carried out using the BIRALES and BIRALET sensors for survey and tracking observations respectively. Finally, the results obtained from observations have been compared with the real positions of the targets in order to validate the system. The ranging method relies on the synchronization of the transmitting and receiving antennas and on the correlation of the echo received from the scattering of the orbiting object. To do that, the transmitting antenna emits simultaneously two different signals: a Chirp signal for range measurement and a second “Continuous Wave” (CW) for Doppler shift measurement and object track reconstruction. Overall, we simultaneously obtain time profiles for range, angular position (azimuth and elevation), and Doppler during the passage of the objects inside the sensor Field of View. By virtue of the above plethora of measurements, this method guarantees also the possibility to produce an Initial Orbital Determination (IOD) for unknown objects