Space–Time Transmission and Coding for Range Ambiguity Resolvability in SAR Imaging

Range ambiguity is a critical challenge in highresolution and wide-swath (HRWS) synthetic aperture radar (SAR) imaging. In this paper, a space-time transmission and coding (STTC) radar framework for resolving range ambiguity is proposed. The STTC employs a small time offset among transmit array elements and two-dimensional element-pulse coding (EPC). An essential signal processing procedure consisting of receive digital beamforming (DBF), pulse compression, and fast-time convolution is proposed. The time offset modulation enables discrimination of different array elements with the pulse compression sub-procedure in fast-time dimension, which obtains transmit spatial degrees-offreedom (DOFs) via fast-time convolution. The proposed technique overcomes ideal orthogonal waveform design in the conventional multiple-input and multiple-output (MIMO) radar. The EPC serves as a unique tag of different range regions, offering the potential to resolve the range ambiguity. The influence of different coding schemes on range ambiguity separation is analyzed, and the tradeoffs and limitations in practical applications are discussed. The transmit beampattern and multi-dimensional ambiguity function of STTC radar under different coding schemes is explored. Simulation results of point and scene targets are provided to validate the effectiveness of the proposed radar framework.