Phase-Coded Passive Jamming Suppression via Squaring Nonlinear Transform and Fractional Fourier Transform

Phase-coded passive jamming (PCPJ) with the capability of harmonic modulation is an emerging threat in the radar detection field. PCPJ is generated by reconfigurable metamaterials with time-varying properties, which is capable of shifting the frequency spectrum of reflected waves. After pulse compression processing of the interfered signal, the deteriorating phenomenon of real target vanishing and false target indistinguishable occurs. Existing jamming suppression methods fail to recover the fundamental frequency spectrum of the real signal shifted by the PCPJ modulation and cannot distinguish the high-fidelity false targets generated by the coherent harmonics. In order to address the shortcomings of existing suppression methods, this article proposes a PCPJ suppression method based on the squaring nonlinear transform and the fractional Fourier transform (FRFT). First, the jamming mechanism under the PCPJ scenario is elaborated. Then, the squaring nonlinear transform is used to recover the real signal frequency spectrum. Inevitably, the nonlinear transform introduces cross-terms in the presence of noise. Finally, the FRFT is used to suppress the cross-terms and improve the signal-to-noise ratio. This algorithm recovers the useful signal components shifted by PCPJ modulation and increases the target-to-jamming ratio. Simulation and experimental results prove the validity of the algorithm.