Orthogonal Coprime Synthetic Aperture Radar

Recently, we have proposed a new synthetic aperture radar (SAR) technique, which we called “Coprime SAR” (CopSAR), applicable to the case of bright targets over a dark background and therefore useful in ocean monitoring for ship detection. The CopSAR technique is based on the adaptation of the coprime array beamforming concept to the case of SAR systems, and, in its basic implementation, it is able to reduce the amount of data to be stored and processed, with no geometric resolution loss. A more complex dual-frequency implementation allows us to additionally obtain a significant increase in the range swath size with respect to the standard SAR technique. However, for both practical and theoretical reasons, the simplest single-frequency implementation is preferable. Accordingly, here, we present an enhancement of the CopSAR basic implementation, based on the transmission of (quasi) orthogonal waveforms, i.e., up- and downchirps: we name it “Orthogonal Coprime SAR” (OrthoCopSAR). The proposed implementation is able to achieve both data reduction and range swath extension with no appearance of ghosts, no resolution loss, and only a limited complication of the required technology. The only costs are the reduction in the target-to-background ratio and the presence of a (nonstringent) limit on maximum ship size, as it is the case in all CopSAR implementations.