Signal Processing for Small-squinted Multi-rotor UAV-borne FMCW SAR

Multi-rotor unmanned aerial vehicle borne frequency modulated continuous wave Synthetic Aperture Radar is attracting more and more attentions due to its low cost and flexible operation capacity, including radar beam steering away from zero Doppler direction which provides opportunities for capturing squint angle dependent scattering information. However it suffers from large trajectory deviation and severe range azimuth coupling. In this paper, we utilize squint minimization technique to decrease this coupling effect. After which, modified Range Doppler algorithm is derived for imaging, taking into account intra-pulse motions during frequency modulated continuous wave sweep. Raw data based Motion Compensation is carried out with a Doppler tracker, as well as Phase Gradient Autofocus and Minimum Entropy based autofocusing algorithms. Finally, Azimuth Nonlinear Chirp Scaling is used for azimuth compression. Imaging results demonstrate the effectiveness of the above signal processing approach.