Accurate Modeling and Analysis of Isolation Performance in Multiport Amplifiers

A Multiport Amplifier (MPA) is an implementation of the satellite power amplification section that allows sharing the payload RF power among several beams/ports and guarantees a highly efficient exploitation of the available DC satellite power. This feature is of paramount importance in multiple beam satellite systems where the use of MPAs allows reconfiguring the RF output power among the different service beams in order to handle unexpected traffic unbalances and traffic variations over time. This paper presents Monte Carlo simulations carried out by means of an ESA in-house simulator developed in Matlab environment. The objective of the simulations is to analyse how the MPA performance, in particular in terms of isolation at the MPA output ports, is affected by the amplitude and phase tracking errors of the high power amplifiers within the MPA

Constraining Scalar-Tensor gravity models by S2 star orbits around the Galactic Center

The aim of our investigation is to derive a particular theory among the class of scalar-tensor(ST) theories of gravity, and then to test it by studying kinematics and dynamics of S-stars around supermassive black hole (BH) at Galactic Center (GC). We also discuss the Newtonian limit of this class of ST theories of gravity, as well as its parameters. We compare the observed orbit of S2 star with our simulated orbit which we obtained theoretically with the derived ST potential and constrained the parameters. Using the obtained best fit parameters we calculated orbital precession of S2 star in ST gravity,and found that it has the same direction as in General Relativity (GR), but causes much larger pericenter shift.Comment: 13 pages, 1 table, 6 figures. Accepted for publication in Facta Universitatis: Series Phys. Chem. Tech. (Invited lecture at Balkan Workshop 2018

ATI and GMTI Performance Analysis of Post-Sentinel-1 SAR Systems based on Simulations using OASIS

With the Sentinel-1 expected to be launched at the end of 2013, ESA is already funding activities to study the next generation of C-band SAR instruments. One of the drivers for these developments is the strong user re-quirement for high resolution and wide swath (HRWS) operations, which can be realized by using Multiple Azi-muth Phase centers (MAPS). The current reference system for a post-Sentinel-1 instrument features a 12.8 m long antenna divided along-track in 8 panels which, on receive, are sampled independently. To investigate the final performance in terms of surface current velocity estimation errors, a full multi-channel SAR simulator for open-oceans (OASIS: Ocean ATI-SAR SImulator) has been implemented. This simulator generates multi-channel raw data corresponding to a time-varying simulated ocean surface that includes all main environmental effects, and uses prototypes of the proposed processing algorithms. A detailed performance analysis in terms of final ATI performance is presented in this paper

Modeling and analysis of GNSS-R waveforms sample-to-sample correlation

The exploitation of global navigation satellite systems Earth-reflected signals to perform ocean mesoscale altimetry from space has been originally proposed at the beginning of the 1990s. This technique is generally defined asPeer Reviewe

GNSS-R altimeter based on Doppler multi-looking

Measuring ocean mesoscale variability is one of the main objectives of next generation satellite altimeters. Current radar altimeters make observations only at the nadir sub-satellite ground track, which is not sufficient to sample the ocean surface with the required spatial and temporal sampling. The GNSS-R concept has been proposed as an alternative observation system in order to overcome this limitation, since it allows performing altimetry along several points simultaneously over a very wide swath. Latest proposed GNSS-R altimeter configurations allow measuring sea height with an accuracy of few decimeters over spatial scales of 50-100 km, by means of a single-pass. This paper proposes an innovative processing and retracking concept for GNSS-R altimeters based on the acquisition of the full delay-Doppler map (DDM), which allows to acquire multiple waveforms at different Doppler frequencies, whose footprints are located outside the typical pulse-limited region. The proposed processing adapts the Synthetic Aperture Radar (SAR) delay-Doppler concept of spaceborne radar altimeters for use in a GNSS-R system. This processing yields additional multi-look with respect to conventional GNSS-R concepts and translates into an improvement of the altimetry performance estimated to be at least 25%-30%, and even higher, depending on the wanted along-track spatial resolution. The proposed processing can also provide measurements with high spatial resolution at best possible performance, and more generally, offers various possibilities for optimal trade-off between spatial-resolution and height estimation accuracy.Peer ReviewedPostprint (published version

A generic simulator for aperture synthesis radiometers

ESA's SMOS mission has demonstrated that Synthetic Aperture Interferometric Radiometers can be a useful tool for Earth observation. Today, the NASA's GeoStar instrument (USA), ESA's GAS instrument (Europe), or CSSAR's GIMS instrument (China) are just three examples of planned geostationary millimeter-wave sounders using synthetic aperture interferometric radiometry for continuous atmospheric monitoring with a much improved spatial resolution. The study of the performance in terms of angular resolution and radiometric performance, and the optimization of this new type of instruments is a complex task that requires dedicated ad-hoc simulators. The SAIPRS (Synthetic Aperture Interferometric Radiometer Performance Simulator) is an ESA project aiming at the development of a generic simulator in terms of receiver architecture and array configuration, including moving antennas (and eventually changing polarization reference frames). This work summarizes the key aspects of the architecture of this simulator.Peer Reviewe

Modeling and analysis of GNSS-R waveforms sample-to-sample correlation

The exploitation of global navigation satellite systems Earth-reflected signals to perform ocean mesoscale altimetry from space has been originally proposed at the beginning of the 1990s. This technique is generally defined asPeer Reviewe

Cross-correlation waveform mode: a critical review

Earth-reflected Global Navigation Satellite System (GNSS) signals have become an attractive tool for remote sensing. Recently it has been proposed as an alternative to the conventional altimetry to estimate the surface height However GNSS-R altimetry offers lower bandwidths and signals power compared to radar altimeters. This implies a poorer altimetry precision, accuracy and resolution per pulse.Also the altimetry precision will be impacted by the impact of the thermal, and speckle noise mainly. This paper gives a critical review of the cross-correlation waveform model.Peer ReviewedPostprint (published version

GNSS-R altimeter based on Doppler multi-looking

Measuring ocean mesoscale variability is one of the main objectives of next generation satellite altimeters. Current radar altimeters make observations only at the nadir sub-satellite ground track, which is not sufficient to sample the ocean surface with the required spatial and temporal sampling. The GNSS-R concept has been proposed as an alternative observation system in order to overcome this limitation, since it allows performing altimetry along several points simultaneously over a very wide swath. Latest proposed GNSS-R altimeter configurations allow measuring sea height with an accuracy of few decimeters over spatial scales of 50-100 km, by means of a single-pass. This paper proposes an innovative processing and retracking concept for GNSS-R altimeters based on the acquisition of the full delay-Doppler map (DDM), which allows to acquire multiple waveforms at different Doppler frequencies, whose footprints are located outside the typical pulse-limited region. The proposed processing adapts the Synthetic Aperture Radar (SAR) delay-Doppler concept of spaceborne radar altimeters for use in a GNSS-R system. This processing yields additional multi-look with respect to conventional GNSS-R concepts and translates into an improvement of the altimetry performance estimated to be at least 25%-30%, and even higher, depending on the wanted along-track spatial resolution. The proposed processing can also provide measurements with high spatial resolution at best possible performance, and more generally, offers various possibilities for optimal trade-off between spatial-resolution and height estimation accuracy.Peer Reviewe