Improved azimuthal resolution of forward looking SAR by sophisticated antenna illumination function design

In comparison to side looking synthetic aperture radar (SAR), in a forward looking SAR it is much more difficult to achieve high angular resolution. The reason for this resolution problem is that terrain points situated symmetrically about the flight path have the same Doppler history, and the gradient of the Doppler frequency is small in the flight direction. A promising way to improve the resolution consists in using minimum variance unbiased (MVU) estimation in the receiver. Unfortunately, MVU estimation leads to undesirable noise enhancement. It is shown that an appropriate method to determine the achievable angular resolution consists in studying this noise enhancement. To minimise the noise enhancement and thus maximise the angular resolution, the author proposes antennas with specific aperture illumination functions. These illumination functions result in radiation patterns which are spread in the angular domain and are simultaneously fine-structured. Quantitative results concerning the noise enhancement and the angular resolution are presented and discussed