How does a digital RF memory work for generating deceptive jamming waveforms?

A digital RF memory (DRFM) is a device that captures an incoming radar signal, digitizes it, stores it in high-speed memory, and retransmits a modified copy to deceive the victim radar. The DRFM is the core technology behind modern deceptive jamming because it produces coherent replicas that are indistinguishable from real target returns through the radar matched filter: (1) Architecture: the incoming radar signal is received by the EW antenna. An RF front end (LNA + downconverter) brings the signal to an intermediate frequency. A high-speed ADC (10-40+ Gsps, 8-12 bits) digitizes the signal. The digitized samples are stored in high-speed RAM (enough to store one or more complete radar pulses). A digital signal processor (DSP or FPGA) modifies the stored samples: adding time delay (range deception), applying frequency shift (velocity deception), adjusting amplitude, or creating multiple copies (false targets). The modified samples are read from memory, converted back to analog by a DAC, upconverted to the radar frequency, amplified, and retransmitted through the jammer antenna. (2) Key parameters: instantaneous bandwidth: 2-8 GHz (modern DRFMs cover the full threat band). Sampling rate: 10-40+ Gsps (must satisfy Nyquist for the instantaneous bandwidth). Memory depth: enough to store 1-100 radar pulses (typically microseconds to milliseconds of signal). Processing latency: 50-200 ns (the retransmitted signal must arrive within the radar range gate). Coherence: the DRFM output is phase-coherent with the input (because it is a digitized copy). This means the retransmitted signal passes through the radar pulse compression filter with full processing gain, making it appear as a real target. (3) Jamming techniques enabled by DRFM: range gate pull-off (RGPO): the DRFM initially retransmits the signal with zero delay (appearing co-located with the real target). Then progressively increases the delay, pulling the radar range gate away from the true target. Velocity gate pull-off (VGPO): the DRFM applies a progressive Doppler shift to the retransmitted signal, pulling the radar velocity tracker away from the true target velocity. False target generation: the DRFM creates multiple delayed and Doppler-shifted copies, each appearing as a separate target on the radar display. Coherent noise: the DRFM modulates the returned signal with noise-like phase or amplitude variations, degrading the radar SNR.