Synthetic Aperture Radar (SAR) systems are installed on both conventional aircraft and satellites. Owing to their significant advantages, they are increasingly employed for various Earth observation tasks, including surface mapping, detection of small objects, acquisition of high-resolution terrain images, and rapid cartographic updates. The implementation of new design principles and advanced signal reception and processing techniques in spaceborne SAR systems enables the formation of signals with a large time–bandwidth product, thereby achieving high spatial resolution. This, in turn, substantially enhances the jamming immunity of spaceborne SAR, particularly against active noise-masking interference generated by electronic countermeasure stations. In this study, an algorithm is developed for generating retransmitted signals in a spaceborne SAR system that enables the estimation of the frequency–time parameters of the probing linear frequency-modulated (LFM) signals and the subsequent synthesis of signal-like interference based on these estimates. By incorporating autocorrelation processing of the received LFM signal, the proposed algorithm enables accurate parameter estimation of LFM signals across various SAR frequency bands, achieving an error of no more than 10% for frequency modulation rates at a signal-to-noise ratio greater than −10 dB. This approach enables the formation of signal-like interference within a retransmitter mounted on an unmanned aerial vehicle.