A Novel PRI Variation Strategy for Range Ambiguity Suppression in Quad-Pol Staggered Spaceborne SAR Based on Azimuth Phase Coding

Staggered synthetic aperture radar (SAR) is compatible with quadrature-polarimetric (quad-pol) SAR, enabling ultrawide continuous swath quad-pol SAR imaging with fine azimuth resolution. However, the quad-pol staggered spaceborne SAR is constrained by severe range ambiguity in the cross-pol channel. Moreover, azimuth phase coding (APC), as an excellent technique for range ambiguity suppression, is no longer exactly effective in the staggered imaging mode because the range ambiguities for different azimuth samples are located at different slant ranges. Given the above challenges presented in quad-pol staggered SAR, in this article, a novel pulse repetition interval (PRI) variation strategy based on APC is proposed to suppress range ambiguity in quad-pol staggered spaceborne SAR. First, the range ambiguity signal for quad-pol staggered SAR is modeled and analyzed. Then, the dedicated PRI variation strategy for quad-pol staggered SAR is developed, by which the near or far first-order range ambiguity is coherent in azimuth and can be subsequently suppressed using APC technique. Especially, a scale factor is developed in the novel PRI variation strategy, which can be flexibly designed to optimize the time interval of alternately transmitted polarized pulses. By this, most of the incoherent far or near first-order range ambiguity energy can be significantly reduced. Finally, simulations are conducted to verify the advancement of the proposed approach for range ambiguity suppression in quad-pol staggered SAR. The work in this article can be viewed as an important candidate for range ambiguity suppression in future quad-pol staggered spaceborne SAR.