Abstract
Radio frequency interference (RFI) is becoming a major concern for future synthetic aperture radar (SAR) missions due to the increased user demand for frequency occupation in a number of applications. Each occurrence 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 in the downlink capacity. This article 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 after downlinking the data and the data volume remains manageable. This is achieved with auxiliary beams. Their concept and limitations are discussed in detail in this article 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 nonorthogonal to the SAR signal.
Highlights
R ADIO Frequency Interference (RFI) refers to signals transmitted by electromagnetic sources external to a Synthetic Aperture Radar (SAR) [1], [2] system
This paper shows that by slightly reducing the flexibility of the spatial filtering, Digital Beamforming (DBF) can be utilized for RFI mitigation without either drawbacks: the processing is performed onground after downlinking the data and the data volume remains manageable
This comes at the cost of an increased system complexity; this complexity is already available in future systems for achieving high azimuth resolution and large swath width at the same time (e.g., Scan-on-Receive [44]) and the same technology can be used for RFI mitigation
Summary
R ADIO Frequency Interference (RFI) refers to signals transmitted by electromagnetic sources external to a Synthetic Aperture Radar (SAR) [1], [2] system. A coherent subtraction of the estimated interference corrects the data without distorting the SAR signal, though the quality of the results depends on the accuracy of the estimation model This is problematic as attaining accurate a-priori information is challenging due to the large spatial and temporal variability of RFI, as mentioned above. The information that is gathered with the additional antenna is coherently subtracted from the data and the RFI is spatially filtered This works well if the RFI direction is known. One advantage of DBF is the forming of the antenna pattern in post-processing [43] This comes at the cost of an increased system complexity; this complexity is already available in future systems for achieving high azimuth resolution and large swath width at the same time (e.g., Scan-on-Receive [44]) and the same technology can be used for RFI mitigation.
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