A review of orthogonal waveforms for spaceborne Multiple-Input Multiple-Output Synthetic Aperture Radar

Spaceborne Multiple-Input Multiple-Output Synthetic Aperture Radar (MIMO-SAR) overcomes fundamental shortcomings of state-of-the-art SAR, such as the trade-off between swath width and spatial resolution, and offers a greater agility of the antenna beam steering. In addition, MIMO-SAR enables a wide variety of new operation and acquisition modes, such as the High-Resolution Wide-Swath (HRWS) mode. One demanding requirement in this subject is to design separable orthogonal waveforms which optimize the overall imaging performance. In the case of a SAR system, this is not an easy task due to the nature of the imaged scene consisting of a multitude of point and distributed targets. This paper summarizes the most promising waveforms in the literature and analyzes them in detail. The selected waveforms are investigated for the first time with respect to their use in SAR using the ambiguity function. As a conclusion, a catalogue of important waveform performance parameters and an ambiguity function analysis are provided, to support the modern MIMO-SAR designer in the form of decision rules for the optimal waveform selection.