In-Orbit Antenna Pattern Measurement of a LEO Radar Satellite by a Small Measurement Satellite Flying in Formation

Abstract

This workshop contribution describes an approach for in-orbit satellite antenna pattern measurement. A small measurement satellite flies in formation with a radar satellite. The quality of a radar satellite mission and its products relies on antenna pattern measurement while the satellite is in orbit. In radar missions like Synthetic Aperture Radar (SAR), the antenna pattern of the radar satellite is measured in orbit by using calibration targets on the Earth’s surface, e.g., corner reflectors or transponders. These on-ground measurements deliver one-dimensional azimuth or elevation patterns within constrained angular ranges. In elevation only a few samples of the pattern are usually obtained since a calibration target is required for each sample. The presented approach allows for a two-dimensional antenna pattern measurement that is able to cover the full angular range in azimuth as well as elevation angle. Numerous central cuts through the two-dimensional pattern are generated by small variations of the measurement satellite’s orbit parameters with respect to the ones of the radar satellite. Since the measurement is performed in free space, there are no distortions from atmosphere, ionosphere, and ground clutter. Also excluded are multipath effects and ambiguities, and volume scattering does do not apply, too. The approach can provide great benefits for future radar missions by allowing accurate and fast two-dimensional in-orbit antenna pattern measurements, especially in case of digital beamforming. Simulations of the satellite’s orbits, gain and angular sampling accuracy analyses are provided in the contribution.