Bandwidth extrapolation of LFM signals for narrowband radar systems

Existing bandwidth extrapolation (BWE) techniques developed for wideband radar systems use stretch processing. A major drawback of these BWE techniques is that the range depth of interest (RDOI) can only be a small fraction of the radar unambiguous distance. This drawback restricts existing BWE techniques from being applied to narrowband radar systems where the RDOI can extend to a significant fraction of the radar unambiguous distance. To address this problem, we formulate a new BWE technique based on matched filtering (MF) and show that the proposed approach allows the RDOI to be as large as the radar unambiguous distance. We demonstrate the capability of the proposed method using both simulated data and real data collected from an over-the-horizon (OTH) radar system. We show that the proposed technique successfully resolves closely spaced targets where conventional range-Doppler (RD) processing technique has failed and is capable of improving the range resolution in the presence of stationary clutter that is 20-50 dB stronger than the targets. In addition to range resolution improvement, we observe that the proposed technique also improves the signal-to-noise ratio (SNR) of the targets.