Contents 1. Introduction
As the most widely used solution for electronic countermeasures, the current digital RF memory (DRFM) is mainly limited by the sampling rate of DACs/ADCs [1]. The instantaneous bandwidth (IBW) of DRFM can only reach 1-2 GHz typically, making it difficult to effectively jam spread spectrum radar signals such as frequency diversity and frequency agility. Microwave photonics offers an attractive approach to overcome the above rate and bandwidth limitations. A photonic RF memory (PRFM) can be implemented based on binary fiber optic delay lines [2], [3] or active fiber optic loops [4]-[6], and its IBW can be extended beyond 10 GHz. However, only range deception can be achieved just through fiber delay, and cannot effectively cope with radars with simultaneous detection capabilities of range and velocity information, such as pulse Doppler radar. To address this problem, a Doppler frequency shift (DFS) structure based on dual-AOM has been proposed and combined with PRFM [5], [6]. These schemes experimentally demonstrated high-fidelity frequency memory and tunable DFS, possessing the ability to perform range and velocity deception synchronously. Nevertheless, the DFS produced by AOMs is fixed each time, and only one Doppler false target can be generated, severely limiting the jamming effects. Additionally, increasing the storage period of signals with higher frequencies remains a critical issue.
