The highly-squinted airborne synthetic aperture radar (SAR) with curved trajectory has significant potential in applications characterized by disaster monitoring and resource exploration due to its flexible flight and wide-area coverage.However,the significant spatially variant phase errors are introduced by large squint angle,leading to severe defocusing or even imaging failure at the scene edges when the traditional imaging algorithms are employed.For this reason,a method of residual spatially variant phase error in compensation for airborne curved trajectory SAR based on the radius/angle algorithm (RAA) is proposed.First,an accurate model of residual spatially variant phase error is established,and its spatial distribution characteristics are deeply analyzed,and then,the analytical expression of the residual phase error in the spatial frequency domain is derived,and a simple and efficient spatially variant phase error compensation filter is designed by establishing a mapping relationship between the slow-time domain and the spatial frequency domain.The filter operates in the spatial frequency domain by using a block-wise processing strategy,effectively eliminating the spatially variant phase errors caused by the curved trajectory and large squint angle.Compared with the traditional algorithms,this proposed method significantly improves imaging quality at the scene edges while maintaining low computational complexity.The simulation and experimental results show that the phenomenon of azimuth defocusing at edge point targets is significantly suppressed,and the image resolution,the peak sidelobe ratio,and the integrated sidelobe ratio are still more close to the theoretical values,enabling the wide-swath imaging under large squint conditions.