Elevation-Interpulse Phase-Coded Waveform: A Novel Radar Waveform for Spaceborne MIMO-SAR

The primary technical challenge for multiple-input multiple-output synthetic aperture radar (MIMO-SAR) systems is separating independent channel responses from aliased echoes while maintaining imaging performance. However, the most promising short-term shift-orthogonal (STSO) and segmented-phase-code (SPC) waveform require the use of elevation digital beamforming (DBF) to achieve echo separation. The cost of using elevation DBF for echo separation is the loss of elevation degrees of freedom and a significant increase in system complexity. To solve this problem, this article proposes a novel coded waveform that introduces phase characteristics for echo separation through 2-D phase encoding of the transmitted waveform in both elevation and interpulse (azimuth) direction. In this scheme, azimuth DBF (ADBF) is used in the Doppler frequency domain to suppress interference signals, while elevation phase demodulation is employed to separate the echoes. This scheme eliminates the dependence of MIMO-SAR on waveform orthogonality and allows the direct use of a large number of single-station waveforms, providing flexibility in waveform selection. In addition, retaining more degrees of freedom enables the multimodal operation of MIMO-SAR. Finally, detailed simulation experiments are performed to verify the potential of the proposed scheme, and advantages and contributions are systematically analyzed.