A contrast-based algorithm for synthetic range-profile motion compensation

In stepped-frequency radar, target motions produce range-profile distortions. Range shift, signal-to-noise ratio loss, and symmetric spreading are produced by target radial velocity, whereas target radial acceleration is mainly responsible for asymmetric smearing. Acceleration-distortion effects are usually negligible when a high Pulse Repetition Frequency (PRF) is used, although this is not the case for low-PRF radars. In this paper, a new motion-compensation technique based on contrast optimization is proposed. The innovative contributions of this paper are as follows: 1) A theoretical analysis of the distortions produced by target motions on the reconstruction of synthetic aperture radar is provided; 2) the proposed technique compensates both phase terms, which are due to target radial velocity and acceleration; therefore, synthetic range profiles can be focused by processing low-PRF radar returns; 3) a new cost function for the synthetic range profiles (namely, contrast) is defined and used for motion compensation; 4) the proposed technique can be applied to any kind of stepped-frequency waveforms; and 5) an estimation error analysis is performed, first theoretically and then by means of both simulations and real data.