A Novel Approach for In-Orbit Satellite Antenna Pattern Measurement Using a Small Satellite Flying in Double-Cross-Helix Formation

The article proposes a novel approach for in-orbit satellite antenna pattern measurement by means of a dedicated small measurement satellite (MES) that flies in Double-Cross-Helix formation. For establishing and maintaining the quality of a satellite mission and its products, antenna pattern measurement while the satellite is in orbit is crucial. In remote sensing missions like synthetic aperture radar (SAR), the pattern is measured using calibration targets on the Earth’s surface. Such on-ground measurements are costly, time-consuming, and only offer 1-D azimuth or elevation patterns within constrained angular ranges. The novel approach provides a 2-D in-orbit measurement that covers the full angular range. The 2-D pattern is obtained from numerous central cuts resulting from small modifications of the MES’s orbit parameters that establish the Double-Cross-Helix formation. The measurement is performed in free space with a single free-flying MES. This avoids all distortions from atmosphere, ionosphere, ground clutter and multipath effects, ambiguities, and volume scattering. The approach is of great value for future satellite missions that are increasingly based on a huge number of electronically steered antenna beams and/or digital beamforming. The Dual-Cross-Helix approach provides faster, cheaper, and more accurate pattern measurements. The article discusses a high-level system concept of a feasible in-orbit pattern measurement of a SAR satellite similar to TerraSAR-X by means of a passive MES that is equipped with a reflecting sphere. Orbit simulations, measurement gain, and angular sampling accuracy analyses verify that the Double-Cross-Helix approach is feasible and advantageous for in-orbit antenna pattern measurement.