Inter-Pulse Phase Modulation Waveform Scheme for Spaceborne MIMO SAR Systems

Special attention has been devoted to multi-input multioutput synthetic aperture radar (MIMO SAR) systems over the past decades. However, performances of such systems are seriously limited by the imperfect orthogonal waveforms. The nonideal orthogonality would introduce ambiguous energy, and therefore degrades the signal to clutter ratio dramatically. In order to suppress the ambiguous energy, the interpulse phase modulation (IPPM) and range-Doppler decouple filtering scheme was proposed. However, this scheme requires a multiplied pulse repeat frequency (PRF), and thus degrades the swath width and/or the azimuth resolution. In this article, the IPPM waveform scheme is further developed to avoid the required increasing of the PRF. With the developments, the MIMO SAR can simultaneously produce multiple higher signal to noise ratio image data without degrading the ambiguities. The multiple images can be used either to realize multimodal operation or to further enhance the noise equivalent sigma zero. Theoretical analysis is validated by numerous simulations.