A novel method of space-borne cognitive SAR signal generation based on FPGA and DDS

Future space-borne cognitive synthetic aperture radar (SAR) can autonomously extract scene environment information in orbit, and use knowledge base and intelligent decision processing technology to quickly adjust radar signal parameters to achieve adaptive detection. Therefore, the space-borne cognitive SAR needs to have the ability to generate signals autonomously and controllably. A controllable generation method of space-borne cognitive SAR signals based on FPGA is proposed in this paper, which introduces the time-domain hybrid sampling technology and uses multiple under-sampling FPGA on-chip direct digital synthesizers (DDS) to work together. It can automatically calculate the phase parameters of each DDS according to the input signal parameters such as the frequency bandwidth, and time width of the radar signal. Multi-channel under-sampled linear frequency modulated signals are generated by the multiple DDS, and then spliced in the time domain and output to an external high-speed DAC to obtain the final intermediate-frequency SAR chirp signals. Simulation analysis shows that the proposed method can generate intermediate frequency SAR signals with any frequency bandwidth in the range of 50MHz to 450MHz, when the high-speed DAC with a sampling rate of 2.0 GSPS is selected. This method can meet the needs of on-orbit intelligent adjustment of space-borne cognitive SAR chirp signals.