Frank Jensen

Improved In-Flight Pattern Retrieval by Reflector-Deformation Fitting

The in-flight pattern measurements of a sub-millimeter space telescope may be improved by determining the actual reflector anomalies, and then including the knowledge of these in the final pattern determination. The pattern measurements with a celestial object as a source often have an insufficient signal-to-noise ratio for pattern prediction outside the main lobe. Repeated measurements may improve this, but even better is the possibility of extracting data from different detectors operating at different frequencies. With the Planck Space Telescope as an example, simulations of a displaced and distorted reflector were carried out for noise-contaminated amplitude measurements of Jupiter by five and 10 different detectors, respectively. First, the main beams of the antenna patterns were retrieved in a regular grid. Here, the accuracy was limited by the noise level. By a Physical Optics optimization, the actual distortions of the telescopes reflector were then determined, so that the calculated radiation patterns of the antenna were correlated to the measured main beams. The patterns for the optimized and retrieved reflector geometry were shown to be precise at levels far below the noise floor in the direct measurements.

A Novel Accurate Pattern Fitting of Noisy Irregular Beam Data for the Planck Space Telescope

Fitting using Kriging, originally developed for geological exploitation, has here been applied for fitting an expected pattern to noisy, irregular, in-flight measurements of a satellite antenna. The noise level in in-flight measurements is often so high that only the central part of the main beam appears. Using the Kriging method, a characteristic function - the regression model - was first fitted to the measurements. For the main beam, this was chosen to be described by a general second-order polynomial. To this was added a more-detailed correlation model, which represented realistic deviations from the regression model but filtered out the fast variations of the noise. The method was applied to simulated measurements of the Planck RF telescope. The results presented showed a considerable reduction of the noise floor of the pattern: even beam details invisible in the original measurements (a shoulder) were revealed by the pattern fitting.

Combining GTD with MOM in analysing the scattering from the LICEF antennas on the SMOS satellite

The present paper describes the determination of the scattering from the LICEF antenna elements on the SMOS satellite taking into account that the solar panels rotate during the flight of the satellite.