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Knowledge of the optical refractive index structure parameter Cn2 is of interest for Free Space Optics (FSO) and ground-based optical astronomy, as it depicts the strength of the expected scintillation on the received optical waves. Focus is given here to models using meteorological quantities coming from radiosonde measurements as inputs to estimate the Cn2 profile in the atmosphere. A model relying on the Cn2 statistical definition is presented and applied to recent high-density radiosonde profiles at Trappes (France) and Hilo, HI (USA). It is also compared to thermosonde measurements coming from the T-REX campaign. This model enables to obtain site-specific average profiles and to identify isolated turbulent layers using only pressure and temperature measurements, paving the way for optical site selection. It offers similar performance when compared to a Tatarskii-based model inspired by the literature.

The future communication systems will use higher frequencies, Ka and Q band. For the implementation of fade mitigation techniques, it is important to have representative time series representing the degradations of the received signal for GEO and LEO satellites. This paper presents a model combining numerical weather prediction software WRF and MultiEXCELL rain cells model in order to have more accurate representation of the dynamics of the attenuation for GEO and non-GEO satellite links.

A long-term investigation of the attenuation in non-rainy conditions has been carried out, for a tropical and a temperate location, using meteorological data and NWP (Numerical Weather Prediction) products during the period 2011-2015. The results show that ERA-5 full profiles are appropriate to estimate non-rainy attenuation in lieu of radiometric or radiosonde observations. Simpler regression-based methods are established. A new formulation for oxygen attenuation is introduced, which only requires surface temperature and pressure. Mass absorption coefficients are used for water vapour and cloud attenuation. Simpler regression-based approaches are then validated. The non-rainy attenuation at K, Ka and Q bands has been found noticeably higher in the tropics than in the temperate region. This study would facilitate the planning of global mobile satellite communication systems

Due to the congestion of the spectrum and the need for wider bandwidths, ultrahigh throughput satellites (UHTSs) are moving towards the use of higher frequency bands (Q/V and W bands). These frequencies are however severely impaired by atmospheric phenomena causing attenuation, scintillation and depolarization and compromising the quality of service (QoS). In order to study the Earth-space link, several experimental campaigns have been performed up to the Q band with geostationary (GEO) satellites. This paper introduces a new propagation experiment that will extend the characterization of the Earth-space channel up to the W band and low Earth orbits (LEOs).

To detect wake vortices in all weather conditions, lidar and radar sensors are complementary. It is important to determine accurately the limitations of the radar detection in clear air and to determine the parameters influencing the detection. This paper is the first study to present the simulation and analysis of the radar signatures of wake vortices on the basis of state-of-the-art 3D large-eddy simulations. The setup of the large-eddy simulations is described and the evolution of the wake vortices is illustrated for the three simulated cases. A modified version of the model developed by Muschinski et al. is used here for the calculation of the radar-backscattered signal and the second moment of the Doppler spectrum that is used to estimate the wake vortex circulation. The simulator uses two different radar configurations for the retrieval of the circulation, which is compared with the circulation obtained directly from the large-eddy simulations. The retrieval of the circulation is fairly accurate if the level of backscattered signal is high enough above the detection threshold of the radar.

The upcoming migration of satellite services to higher bands, namely, the Ka‐ and Q/V‐bands, offers many advantages in terms of bandwidth and system capacity. However, it poses challenges as propagation effects introduced by the various atmospheric phenomena are particularly pronounced in these bands and can become a serious constraint in terms of system reliability and performance. This paper presents the goals, organisation, and preliminary results of an ongoing large‐scale European coordinated propagation campaign using the Alphasat Aldo Paraboni Ka/Q band signal payload on satellite, performed by a wide scientific consortium in the framework of a European Space Agency (ESA) project. The main objective of this activity is the experimental characterisation of the spatial and temporal correlation over Europe of the radio channel at Ka and Q band for future modelling activities and to collect data for development and testing of fading mitigation techniques.

A pair of counter-rotating vortices is created after roll-up of the wake of flying aircraft. Normally, wake vortices cannot be observed visually unless they capture some smoke, clouds, or aircraft contrails. Nevertheless, wake vortex turbulence is a serious hazard for the following aircraft especially during taking off and landing. The aircraft encountering a wake vortex system that has not dissipated enough, may be subjected to a strong rolling moment or to a strong downwash velocity causing a drop in lift. To prevent such a risk, safety separations between aircraft were imposed by ICAO at the beginning of the 70s. With the exponentially growing air traffic, those safety separations become too constraining for large and busy airports, limiting their capacity and flexibility, and causing many delays on departures and arrivals. In order to support the development of new systems, such as weather dependent separation, measurement tools are required, to provide in real time, information about the wake vortices intensity and their location relative to the glide path. The main sensors proposed are lidar and radar. They are complementary to detect wake vortices in all weather conditions: lidar is used in clear air and radar in rain. It is important to determine accurately the limitations of the radar detection and the parameters influencing them. This thesis provides a tool that allows the simulation of the wake vortices detection by radar in clear atmosphere and in the presence of rain. It can be used to optimize the radar parameters, to develop algorithms for the detection of wake vortices and to estimate their parameters. The novelty of the approach resides in the use of 3D fields from Large Eddy Simulations (LES) of the wake vortices in the turbulent stratified atmosphere, for the calculation of the radar backscattered signal. The LES output is used to simulate the time series and the Doppler spectra of the signal returning to the radar. The simulated signal is then an, (FSA - Sciences de l'ingénieur) -- UCL, 2019

Mobile-to-Mobile (M2M) communication is a challenge, but fast growing since it has the potential to enhance the quality of data service with low energy consumption. This dual mobility generates non-stationarity properties of the propagation channel, which requires precise modeling, for simulation network and system design. This thesis aims for characterization and modeling of M2M channels based on stochastic approaches. Some common M2M aspects like the non-stationarity, Doppler and correlation properties were also analyzed. Stochastic channel models were proposed for Body to Body (B2B) and Vehicle to Pedestrian (V2P) channels based on measurements. The non-stationary fading behavior were observed as a function of mutual body orientation and the relative Tx-Rx distance. A general model for the auto-correlation function of the fading channel was derived assuming a typical M2M scenario in the presence of moving scatterers; and a simplify Doppler spectrum model was also developed for indoor M2M scenarios. Both models allow to reproduce with good accuracy the correlation and Doppler properties of different M2M scenarios including line-of-sight (LoS) and non-line of sight (NLoS) environments. Finally, implementation techniques able to reproduce the fading characteristics of M2M channels including the Doppler and correlation characteristics were proposed and successfully compared to the measurements., (FSA - Sciences de l'ingénieur) -- UCL, 2018

Space missions present antenna designers with a unique set of requirements. Not only does the antenna need to perform optimally from the electromagnetic radiation point of view, but also need to survive launch conditions, perform optimally at extreme temperatures, deter ionizing radiation, and provide electrostatic protection. Furthermore, without any prospect of repair, such antennas need to be robust enough to withstand the harsh environment on its own. This thesis work touches upon such multi-physics approach to antenna design. More specifically, the antennas concern the ones for the Lander Radioscience (LaRa) instrument intended for the surface platform of the ExoMars 2020 mission to Mars. The antennas would allow direct communication with Earth irrespective of the orientation of the surface platform when it lands, and allow observation throughout the year. This is possible through the conical radiation patterns, which have uniform elevation pattern over the azimuthal plane along the surface platform. For space communications, it is a necessity to have circular polarization as well. Therefore, the thesis proposes different topologies of circularly polarized conical beam antennas ideal for space communications, from planar antennas to 3D metallic antenna. Concerning the planar antenna technology, a circular slot array and a circular patch antenna were developed. The multi-layered PCB structure requires a careful design given the need for space qualification, due to the thermoelastic effect. Metallic antennas are deemed more appropriate to counter such effect, since the homogeneous material properties of the metallic antennas ensure better performance under the thermoelastic stress. To that end, a novel 3D metallic antenna is proposed which is based on gamma-shaped vertical posts surrounding a centrally radiating monopole. Moreover, a numerical method to analyze the near-field performance of the antenna has also been proposed. Especially in the case of space anten, (FSA - Sciences de l'ingénieur) -- UCL, 2018

With the move of satellite systems towards Ka and Q/V bands, the Alphasat TDP5 Aldo Paraboni scientific experiment aims to characterize atmospheric attenuation in those bands. However, during the retrieval of the attenuation from the measured beacon signal, the clear-sky contribution to attenuation is lost. Microwave radiometers give the clear sky absolute reference level, but these are costly and not always available. This paper proposes Numerical Weather Prediction models as an alternative source of clear-sky attenuation. Three months of beacon and radiometric data from Spino d’Adda Alphasat receiving station are used as benchmark for the validation of the method. A preliminary conclusion is that gaseous attenuation is well predicted, but cloud attenuation is underestimated.

This paper presents rain attenuation statistics for satellite-ground transmission links at Ka-band based on ten-year reflectivity observations from a C-band weather radar. The ground receiving station and the radar are both located in Belgium. Only precipitation under the freezing level is considered and the attenuation produced by hail is removed by applying a reflectivity threshold. The radar-derived attenuations are analyzed to investigate the influence of elevation and azimuthal angles on the attenuation statistics. It is shown that the azimuthal dependence is extremely low. In contrast, the exceedance probability for a given attenuation threshold strongly increases with decreasing elevation angles, as foreseen by ITU-R recommendations. The radar-derived attenuations are used to estimate rain attenuation CCDFs computed according to ITU-R recommendations for a LEO satellite. The sensitivity to the hail reflectivity threshold is very limited. In contrast, our results show that reliable attenuation statistics cannot be obtained without taking carefully into account the height of the freezing level. Monthly averages of the freezing levels allow producing satisfactory results but it is recommended to incorporate freezing level heights with high temporal and spatial resolutions.