On-Ground RFI Mitigation for Spaceborne Multichannel SAR Systems using Auxiliary Beams

Radio Frequency Interference (RFI) has become a major concern for future Synthetic Aperture Radar (SAR) missions. Each occurence of interference introduces artifacts in the radar imagery, biasing the measurements and leading to erroneous results. In addition to conventional techniques, the use of multichannel SAR for RFI mitigation has been proposed because its Digital Beamforming (DBF) capability allows for a spatial filtering of the received signals. Thereby it becomes possible to remove RFI that arrives from a different direction than the SAR signal. Past publications on the topic presented highly flexible spatial filtering techniques. Those methods require either additional on-board processing or a substantial increase of the downlink capacity. This paper shows that by slightly reducing the flexibility of the spatial filtering, DBF can be utilized for RFI mitigation without either drawbacks: the processing is performed on-ground and the data volume remains manageable. This is achieved with auxiliary beams. Their concept and limitations are discussed in detail in this paper and are supported with simulated RFI mitigation results. Furthermore, it is shown that the information collected with an auxiliary beam can also be used to filter the RFI signal when it is spatially non-orthogonal to the SAR signal