Electromagnetic Gap Leakage Analysis for the SKA Mid-Frequency Dish

This paper presents electromagnetic analysis as performed on the Square Kilometre Array (SKA) mid-frequency dish in order to estimate the ground leakage caused by gaps in the main reflector. The effects of the ground leakage are shown in terms of conventional performance parameters such as gain and aperture efficiency, as well as the percentage of feed power hitting the ground behind the main reflector. Analysis were performed for SKA Band 1 and 2 with a combined frequency range of 0.4 - 1.8 GHz. It is shown that the gaps in the main reflector reduce the gain between 0.23 and 0.05 dB and could increase the noise temperature by approximately 14 K when pointed at zenith. The transmission percentage of the incident power hitting the ground is below 0.2% across the combined bands

Electromagnetic analysis and preliminary commissioning results of the shaped dual-reflector 32-m Ghana radio telescope

This paper presents results from the electromagnetic analysis of the African VLBI Network shaped Ghana radio telescope at the operating frequencies of 5 and 6.7 GHz. The geometry implemented in commercial electromagnetic software provides insight into the effects of the slanted beam-waveguide, shaped reflector illumination and mechanical tolerances, which are known to be more stringent compared to a perfect paraboloid. It is shown that the theoretical maximum gain and aperture efficiency at 5 GHz are 63.80 dBi and 85.45%, respectively. The corresponding values at 6.7 GHz are 66.47 dBi and 88.00%, respectively. Comparisons to sidelobe maps produced from astronomical observations are also discussed, showing possible misalignment in the structure when utilised outside its originally intended purpose

Feasibility Study of Angular Super-Resolution with the Active Surface of a Radio Telescope

The concept of super-resolution refers to various methods for improving the angular resolution of an optical imaging system beyond the classical diffraction limit. A feasible method to design antennas and telescopes with angular resolution better than the diffraction limit consists of using variable transmittance pupils. The simplest transmittance pupils are binary phase shifts masks, also known as Toraldo Pupils, consisting of finite-width concentric coronae which modify the phase of the incident wavefront. In this work we present a preliminary feasibility study to determine if and how the active surface of the 32m Noto radio telescope can be used to modify the wavefront in the same way a Toraldo Pupil would do. Our preliminary analysis suggests that an ideal reflector with fully independent active panels would be able to achieve the super-resolution effect, but the real Noto active surface, where each actuator is connected to four distinct panels, adversely affects the operation of the simulated Toraldo Pupil. We are planning to apply the same analysis to the shaped active surface of the Sardinia Radio Telescope

Inaugurata la più grande antenna radioastronomica italiana

Con una cerimonia estremamente suggestiva è stato di recente inaugurato il Sardinia Radio Telescope. Oltre a numerose autorità nazionali e locali ed un’ampia rappresentanza di scienziati provenienti dai principali centri internazionali di radioastronomia, alla cerimonia hanno partecipato circa 2000 cittadini giunti dai comuni limitrofi interessati a conoscere questo nuovo “vicino di casa”. Risalta infatti in un passaggio naturalisticamente incontaminato, quale è il sito di Pranu Sanguni, questo nuovo impianto dalle dimensioni imponenti e costruito con tecnologia avanzatissima tale da renderlo uno dei più evoluti e potenti strumenti del mondo per lo studio delle emissioni radio provenienti dai corpi celesti e per applicazioni di geodinamica e di scienze spaziali.The Sardinia Radio Telescope was recently inaugurated in the course of an impressive ceremony. In addition to the representatives of local and national authorities, and scientists from leading centres of radio astronomy all over the world, the ceremony was also attended by around 2,000 local people from the nearby areas who were curious to meet this ‘new neighbour’ of theirs. This new installation of spectacular dimensions does indeed stand out in the unspoilt natural landscape of the site of Pranu Sanguni. Built with groundbreaking technology, it is in fact one of the most evolved and powerful instruments in the world for the study of radio emissions originating from celestial bodies and for geodynamics and space science applications

Electromagnetic modelling of the 32-m Ghana radio telescope

This paper presents the electromagnetic modelling and supporting results of the African VLBI Network (AVN) Ghana radio telescope at the operating frequencies of 5 and 6.7 GHz. Working from limited technical data, we establish suitable geometrical parameters for the unshaped version of the Cassegrain system, including modelling and rotation of the four mirrors within the slanted beam-waveguide (BWG). The geometry implemented in GRASP (General Reflector Antenna Software Package) produces several performance values including the effects of the BWG, struts and mechanical tolerances. It is shown that the theoretical maximum gain and aperture efficiency at 5 GHz are 63.09 dBi and 72.56%, respectively. The corresponding values at 6.7 GHz are 65.80 dBi and 75.42%, respectively

Compatibility studies between Radio Astronomy and three upcoming technologies

In recent years, the increased use of high-frequency technology in the millimetre and microwave range, including mobile phones, automobiles, and industrial equipment, has further reduced and threatened the spectrum assigned to the radio astronomy service (RAS). As a scientific and passive service, RAS requires protection from commercial services to observe the extremely faint celestial signals. As spectrum use for land, air, and space communications grows, protecting RAS operations from radio frequency interference is becoming more challenging. This report examines the impact of advanced technologies on radio astronomy, specifically car radar at 77 GHz, 5G and Wi-Fi device deployments at 6.6 GHz. These technologies are evaluated for their potential impact on Italian radio telescopes: the Radio Observatories of Medicina and Noto and the Sardinia Radio Telescope (SRT). Of particular concern is the potential threat posed by car radars to future high-density prospects, as well as the historical importance of the 6.6 GHz frequency for radio astronomical observation of methanol emissions from stars

Measurement of the LOFAR-HBA beam patterns using an unmanned aerial vehicle in the near field

An unmanned aerial vehicle (UAV) is exploited to characterize in situ the high-band antennas (HBAs) of the low-frequency array (LOFAR) CS302 station located in Exloo, The Netherlands. The size of an HBA array is about 30 m. The Fraunhofer distance (a few kilometers) is not reachable in the frequency band (120 to 240 MHz) within the flight regulation limits. Therefore, far-field patterns cannot be directly measured. The UAV, equipped with an radio frequency synthesizer and a dipole antenna, flies in the near-field region of the considered array. Measurement of three different frequencies (124, 150, and 180 MHz) is efficiently made during the same UAV flight. The near-field focusing method is exploited to validate the far-field pattern of the array under test within an angular range around the beam axis. Such a technique avoids both the time consuming λ∕2 sampling of the aperture field and the further application of computationally heavy near-field to far-field transformations. The array beam is well reconstructed in the main lobe and first sidelobes within a 2D scan plane sampled with a radial raster. A further postprocessing technique is proposed and validated on a subarray of HBAs. It suggests efficient ways for the future characterization of regular aperture arrays for SKA-MID Phase 2

Effect of Conductive Propellers on VHF UAV-based Antenna Measurements: Experimental Results

Professional Unmanned Aerial Vehicles (UAVs) are generally equipped with carbon fiber propellers. Their conductivity and significant size can potentially increase both noise and systematics of UAV-based antenna measurement systems operating in the VHF band. A set of alternative fiberglass propellers has been manufactured and tested. This paper present measured results on the signal stability achieved with both fiberglass and carbon-fiber propellers at 175 MHz

UAV-aided calibration for commissioning of phased array radio telescopes

Calibration of antenna positions and instrumental response is a crucial step in the commissioning of a phased array radio telescope. The Low Frequency Aperture Array system of the Square Kilometre Array (SKA) is envisaged to consist of about 131,000 antennas. In this paper, we propose a strategy to efficiently conduct commissioning calibration of such a large phased array radio telescope using a near-field probe mounted on an nmanned Aerial Vehicle (UAV). We demonstrate the effectiveness of the proposed method using simulations. This indicates that potentially cost-saving relaxation of requirements on placement accuracy is possible. We also propose to validate this method in practice using the Low Frequency Array (LOFAR)