Wideband LFM Interference Suppression Based on Fractional Fourier Transform and Projection Techniques

A novel wideband LFM interference suppression method is proposed based on fractional Fourier transform (FRFT) and projection techniques. By using the concentration property of LFM interferences in fractional Fourier domain, the initial frequency, frequency modulation rate and direction-of-arrival (DOA) of LFM interferences are first estimated. Afterwards, the space–time interferences subspace is constructed. In order to suppress wideband LFM interferences, the received signal is projected onto the subspace orthogonal to the interferences subspace when the signals are uncorrelated. Furthermore, considering the scenario when the signals are coherent, according to the properties of oblique projection, LFM interferences are suppressed by projecting the received signal onto the joint signal–noise subspace. Then, the desired signal is extracted by beamforming. Unlike the existing algorithms, the proposed method not only can exactly estimate parameters and directly solve the DOA of LFM interferences but also can construct the interferences subspace with the time-variant steering vector of interferences. Moreover, our method can effectively suppress LFM interferences without reducing the freedom, and significantly improve the performance, even at low signal-to-noise ratio (SNR) or small number of snapshots. Simulation results demonstrate the effectiveness of the proposed method.