Abstract:

There exists serious coupling between azimuth and range for synthetic aperture radar (SAR) in high squint mode.A swath image is defocused in normal nonlinear chirp scaling (NCS). To eliminate the coupling, an improved NCS is proposed. First, the coupling phase above second-order is compensated in frequency domain. Then in the first chirp scaling step, a fourth-order model is used in range Doppler domain. Meanwhile a constant factor is adopted to overcome the constraint of Doppler reference frequency beyond the scope of Doppler frequency. Finally, the influence of the constant factor is eliminated through the second scaling step. Simultaneously, the influence of swath width on the range frequency modulation ratio error is analyzed so as to define a perfect one. Simulation results illustrate that the improved algorithm can fulfill the focusing of the whole swath and satisfy the imaging quality of SAR in high squint mode.