Wednesday, September 5th, 2018, 8:45-10:30
INAF-Astronomical Observatory of Trieste, Loc. Basovizza 302, 34149 Trieste, Italy
Solar Radio Interferences on Radio Systems: A Direct Space Weather Effect
The Sun is a source of broadband radio noise, which can reach quite high levels at different phases of the solar activity cycle. In particular, very intense solar radio bursts can significantly affect the quality of radio communications, e.g. in HF and UHF (mobile phones, radars), up to the interruption of services like satellite geolocation via GNSS in L-band. The Trieste Solar Radio System (TSRS) has played a key role in the detection of one of the first GNSS solar RFI published in literature. In this work, we briefly review the phenomenological scenario by focussing on the observational requirements for GNSS, which operate in the Right-Hand Circular Polarisation mode, and point out the need of a network of dedicated multichannel solar radio polarimeters for providing alerts and warning to enhance the quality of GNSS services and their resilience with respect to solar RFIs, a direct Space Weather effect on technological systems.
LTCI, Telecom ParisTech, 46 rue Barrault 75013, Paris, France
Statistical methods for joint antenna-radio channel modelling
The description of the electromagnetic behavior of antennas needs a large amount of data to be complete, since it requires complex numbers for the radiated far field in all possible directions and polarizations, for all frequencies of interest and all antenna elements in case of arrays or multiport antennas, plus the full impedance matrix. In addition, since most of the time the radio channel linking the transmitting and receiving antennas in a wireless communication is not in free space, many propagation effects are involved and result in the particularities of the received signals. Finally, while it is often designed and measured in nearly ideal conditions (e.g. anechoic chamber) an antenna is rarely used in emptiness and its close environment does impact its performance, sometimes dramatically. While strong close disturbers can be taken into account at the design phase (such as a casing or a human head), variations in the effective impact of such disturbers can take place, which to some extent can unpredictably affect the antenna characteristics. Deterministic methods can hardly take into account all the variabilities that occur in real life and would be much too expensive to implement and to use. The natural approach, widely practiced in other domains, is to resort to statistical descriptions, based on metamodels able to represent these variabilities with a limited number of parameters while achieving an adequate trade-off between accuracy and simplicity. The presentation will address these issues for joint antenna-channel modelling, giving some examples about the development and use of such methods.
Institute of Electrical Engineering and Information Technology
Kiel University, Germany
Scattering and Diffraction of Complex-Source Beams by Canonical Objects
The presentation reviews recent advances in the application of complex-source beams (CSB) as incident fields in the context of scattering and diffraction by canonical objects like wedges, cones and sector-like structures. A CSB can be achieved by simply replacing the source coordinates in the Green’s function by suitably chosen complex numbers. Nearby the axis it then represents half of a Gaussian beam which – except of the waist – exactly satisfies the Maxwell or Helmholtz equations. The main advantages of using CSBs as compared to the commonly applied illuminating plane waves are a dramatically improved convergence of the resulting series expansions of the scattered far fields and the opportunity to illuminate just the desired part of the canonical object, for example the tip of the cone. To achieve results comparable to the case of an incident plane wave a uniform CSB will be employed representing a full Gaussian beam. The uniform CSB will be located such that its waist where the field can be interpreted as a local plane wave interacts with the structure of interest, for example the tip. The outcomes can be used to extend the application of asymptotic methods like the Geometrical Theory of Diffraction (GTD) or the Uniform Theory of Diffraction (UTD). More generally, (uniform) CSBs can also be used as wave propagators in different applications where localized or beam-like fields are more suitable than omnidirectionally radiated fields or full plane waves.
Prof. Gabriele Gradoni
University of Nottingham
Nottingham NG7 2RD