Subspace Projection Algorithm based on Code Agile Waveform for Folded Clutter Suppression

The Internal Clutter Motion (ICM) results in an expansion of the clutter Doppler spectrum. With conventional waveforms, the presence of range ambiguity causes short-range strong clutter with ICM to be folded into the long-range interval. The folded clutter, along with Doppler expansion, submerges low-speed small targets, significantly affecting the target detection performance of ground-based early warning radar. Agile waveforms improve the distinguishability of echoes from different range intervals by varying the waveform parameters between pulses, enhancing the degree of signal processing. Therefore, this paper proposes a subspace projection algorithm based on code agile waveform to suppress the folded clutter with ICM. First, the clutter subspace is constructed using the echo model of the code agile waveform and the distribution characteristics of clutter in the range-Doppler domain. Next, subspace projection is applied to each range interval, with iterative processing between intervals to achieve folded clutter suppression. Finally, the joint mismatch filtering and Pulse Doppler (PD) processing is performed to realize coherent accumulation in each range interval. The simulations and processing results of real measured data demonstrate the effectiveness of the proposed algorithm in suppressing folded clutter and improving the detection performance of small targets at long-ranges and low-speeds.