In-Orbit Two-Dimensional Feed-Array Pattern Measurement for Digital Beamforming SAR Using a Double-Cross-Helix Formation

The paper introduces the in-orbit antenna pattern measurement by a dedicated small measurement satellite flying in Double- Cross-Helix formation. Two approaches are discussed, one with a fixed difference in the ascending nodes and one with a drifting difference. Both approaches provide a full two-dimensional pattern measurement in azimuthal and polar angle. The fixed approach is faster but requires a few more active orbit maneuvers of the measurement satellite. A third approach provides elevation angle cuts at different azimuth angles. It is particularly advantageous for feed-array-reflector based digital beamforming systems, but is also of interest for classical SAR systems. A quantitative example is provided for an L-band SAR system with digital beamforming, i.e., Tandem-L. Orbit simulations verify the proposed approaches.