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SOXS (Son Of X-Shooter) is a single object spectrograph offering a simultaneous spectral coverage from U- to H-band, built by an international consortium for the 3.58-m ESO New Technology Telescope at the La Silla Observatory. It is designed to observe all kind of transients and variable sources discovered by different surveys with a highly flexible schedule maintained by the consortium, based on the Target of Opportunity concept. SOXS is going to be a fundamental spectroscopic partner for any kind of imaging survey, becoming one of the premier transient follow-up instruments in the Southern hemisphere. This paper gives an updated status of the project, when the instrument is in the advanced phase of integration and testing in Europe, prior to the activities in Chile., Proc. SPIE 12184, Ground-based and Airborne Instrumentation for Astronomy IX, 121840O (2022)

The near-field (NF) acquisition time depends on the sampling strategy and on the measurement hardware. Optimised sampling based on singular value optimisation dramatically reduces the number of measurement points and the scanning path length compared to conventional samplings, without impairing the far-field reconstruction. Furthermore, an optimised control approach, tracking a sufficiently smooth trajectory allows better performance in terms of velocity and precision, significantly reducing the scanning time. We show that the combined use of an optimised sampling and an optimised controller drastically reduces the measurement time. The sampling strategy provides a raster grid of optimally selected rows hosting samples optimally arranged according to a row-wise non-uniform distribution. The optimised control drives the NF scanner and the vector network analyser to acquire the data along each row by a continuous probe movement with a variable velocity, accelerating and decelerating between two consecutive sampling points. The sparsity of the NF locations enables a significant increase in the average speed between two consecutive points. The controller is realised with a proportional-integral-derivative law with a compensation signal and a filter downstream. The controller does not demand complex hardware and can be realised in an extremely simple, cheap and off-the-shelf solution.

A tracking problem is considered for a very recurring class of systems, such as Cartesian robots with real actuators, conveyor belts, and certain scanning devices used for medical and engineering applications, as near-field antenna characterization. Theorems are proven for the design of a PID controller with a possible compensation signal to track sufficiently regular trajectories with a prescribed maximum error. The developed design methodology is used to identify the current antenna scanning system without a controller and to design and construct a new controller that provides better performance than the current one. Moreover, this paper proposes an optimized raster scan acquisition scheme that reduces the number of field samples and the scanning path length compared with the more conventional approaches. By using the new controller and the proposed optimized sampling strategy, which provides a sparse distribution of the samples, the performance of an antenna can be evaluated in a considerably shorter time than that necessary using the pre-existing controller and standard scanning, as experimentally assessed in this paper.

An optimized Near-Field antenna characterization is presented based on an optimized number and distribution of the sampling points and on an optimized controller able to exploit the performance of the scanning system. Indeed, to take full advantage of the optimized sampling grid and to reduce the measurement time, a Proportional-Integral-Derivative (PID) control system has been developed to drive the Near-Field scanner and to follow a general trajectory traversing the samples arranged on a raster grid. The performance of the control system is experimentally assessed by a comparison with a standard approach

We present an approach for a fast and accurate determination of the geometrical optics solutions to Maxwell's equations based on the determination of the eikonal function and devised to handle scenarios involving complex spatially varying refraction indices. The explicit solution of the eikonal equation allows to set up an inverse ray tracing scheme, which proves particularly convenient compared to direct ray tracing. The field amplitude and polarization are then found by solving the relative transport equations along each ray. The accuracy of the method is shown in the case of the scattering from a conducting sphere coated by a dielectric. © 2017 ACES.

An innovative method for the diagnosis of large reflector antennas from far field data in radio astronomical application is presented, which is based on the optimization of the number and the location of the far field sampling points required to retrieve the antenna status in terms of feed misalignments. In these applications a continuous monitoring of the Antenna Under Test (AUT), and its subsequent reassessment, is necessary to guarantee the optimal performances of the radiotelescope. The goal of the method is to reduce the measurement time length to minimize the effects of the time variations of both the measurement setup and of the environmental conditions, as well as the issues raised by the complex tracking of the source determined by a prolonged acquisition process. Furthermore, a short measurement process helps to shorten the idle time forced by the maintenance activity. The field radiated by the AUT is described by the aperture field method. The effects of the feed misalignments are modeled in terms of an aberration function, and the relationship between this function and the Far Field Pattern is recast in the linear map by expanding on a proper set of basis functions the perturbation function of the Aperture Field. These basis functions are determined using the Principal Component Analysis. Accordingly, from the Far Field Pattern, assumed measured in amplitude and phase, the unknown parameters defining the antenna status can be retrieved. The number and the position of the samples is then found by a Singular Values Optimization (SVO). © 2016 AMTA.

The communication presents an innovative method for the diagnosis of reflector antennas in radio astronomical applications. The approach is based on the optimization of the number and the distribution of the far field sampling points exploited to retrieve the antenna status in terms of feed misalignments, this to drastically reduce the time length of the measurement process and minimize the effects of variable environmental conditions and simplifying the tracking process of the source. The feed misplacement is modeled in terms of an aberration function of the aperture field. The relationship between the unknowns and the far field pattern samples is linearized thanks to a Principal Component Analysis. The number and the position of the field samples are then determined by optimizing the Singular Values behaviour of the relevant operator. © 2016 SPIE.

We develop an approach for a fast and accurate determination of the Geometrical Optics solutions to Maxwell's equations based on the determination of the eikonal function. The approach, here presented for a 3D problem, is devised to handle scenarios involving complex spatially varying refraction indices. A new solution to a critical issue related to matching of computational grids across scatterers' boundaries is introduced. The explicit solution of the eikonal equation allows to set up an inverse ray tracing scheme, which proves particularly convenient as compared to direct ray tracing. Inverse ray tracing is performed using techniques from computer graphics improving computational performance. The field amplitude and polarization are then found by solving the relative transport equations along each ray.

This paper describes the active optics system of the VLT Survey Telescope, the 2.6-m survey telescope designed for visible wavelengths of the European Southern Observatory at Cerro Paranal, in the Atacama desert. The telescope is characterized by a wide field of view (1.42 deg diameter), leading to tighter active optics than in conventional telescopes, in particular for the alignment requirements. We discuss the effects of typical error sources on the image quality and present the specific solutions adopted for wavefront sensing and correction of the aberrations, which are based on the shaping of a monolithic primary mirror and the positioning of the secondary in five degrees of freedom.