Multipath Interference Removal in Receivers of Linear Frequency Modulated Radar Pulses

The article describes algorithms for the retrieval of linear frequency modulated (LFM) pulses from a received signal which is corrupted by noise and multipath reflections from ground and stationary objects. Such a problem appears, for example, in electronic intelligence (ELINT) or spectrum sensors that receive and analyze signals originating from an active radar emitting LFM signals. Two computationally efficient methods to solve this problem are presented in this paper. The first is a version of time-frequency filtering based on spectrogram zeros. The second method is based on the chirp rate estimation, fractional Fourier Transform (FrFT) and band-pass filtering to retrieve the original pulse signal. Both of the techniques presented were tested using synthetic signals to measure their statistical properties and then positively verified on real-life recorded signals originating from a non-cooperative radar.