A refined frequency scaling algorithm for spaceborne spotlight synthetic aperture radar (SAR) imaging is presented.The algorithm can process dechirped raw data directly.Based on the squinted range equivalent model that is fitter for spaceborne geometrical relation than the broadside range model

the complete derivation of the algorithm is presented and the refined frequency scaling factors of each signal domain are given.The refined factors can process the secondary range compression more accurately and avoid that range bandwidth is aliased or shifted outside the processed bandwidth for squinted mode.The refined azimuth scaling factor can decease azimuth time expansion and improve efficiency of azimuth processing.Besides

in order to decrease very high pulse repetition frequency (PRF) and data rate of spaceborne spotlight SAR and alleviate the design difficulties of spaceborne system

a subaperture approach is introduced.The necessity and implementation of the subaperture approach are analyzed.Finally

the computer simulation shows the validity of the refined algorithm.