Improved DBF-MIMO-SAR Waveform Transmission Scheme for Reducing the Cost of DOF in the Elevation

The echo separation solution based on digital beamforming (DBF) in the elevation is quite applicable to multiple-input multiple-output (MIMO) synthetic aperture radar (SAR). For the current DBF-MIMO-SAR schemes, however, at least 2M - 1 subapertures in the elevation must be employed to successfully separate the aliased signal returns induced by the M simultaneously transmitted waveforms, which essentially increases the system complexity. To this end, this article proposes an improved waveform transmission scheme to exploit the potential benefits that the MIMO concept can provide for a practical remote sensing system with limited available channels. In this scheme, the basic signal segments are coded by the improved phase coding matrix, which is associated with the slow time. Afterward, time-shift weighting, using the decoding matrix, is implemented to remove the interference from close arrival angles. In this process, the interference segments in near or far range can also be canceled out. Consequently, the number of interferences has been halved, and thereby, compared with the already-proposed DBF-MIMO-SAR schemes, e.g., short-term shift-orthogonal, the designed scheme only needs M elevation channels for the realization of DBF-MIMO-SAR. Finally. numerous simulations have been carried out to demonstrate that the proposed scheme shows great potential in terms of echo separation for channel-limited MIMO SAR systems.