A microwave photonic radio frequency memory with tunable delay resolution and Doppler frequency shift

Radar target simulation is essential for radar development. In this paper, a microwave photonic radio frequency memory (RFM) is proposed and experimentally verified. The input radio frequency (RF) signals are delayed and stored in a recirculating loop with a 4-bit binary optical true time delay line (OTTDL), which enables the achievement of the tunable delay resolution and multiple replications. The Doppler frequency shift (DFS) of the delayed signals is achieved by a Mach-Zehnder modulator (MZM) and two cascaded acousto-optic modulators (AOMs), which facilitate a wide tuning range, high precision, and a high spurious suppression ratio (SSR). The experimental results demonstrate that the system has 16 distinct delay resolutions ranging from 0.045 us to 7.576 us. Furthermore, 30 circulations are achieved in the test, indicating that the theoretical maximum storage time is approximately 225 us. Additionally, the frequency shift for 1 GHz-18 GHz RF pulse signals can be tuned over a range of 10 Hz to 10 MHz, with a SSR exceeding 40 dB.