Clutter Rejection for FM Ranging Airborne Radar

In airborne radar, it is important to reject clutter signals to detect targets of interest. High pulse repetition frequency (HPRF) waveform provides robust detection performance in a clutter environment by separating clutter signals from the target echo signals in a Doppler frequency domain, but it suffers from range ambiguity. The range ambiguity in HPRF can be resolved by frequency modulation (FM) ranging. However, the Doppler frequencies of both the clutter and target echo signals change linearly with the range due to changes in the carrier frequency in FM ranging. In such a case, the target echo signal can be rejected by a conventional clutter rejection frequency even if it is not masked by a clutter signal. This paper proposes an optimum clutter rejection frequency for FM ranging airborne radar by considering the Doppler frequency spread in FM ranging. The optimum clutter rejection frequency is derived by calculating the maximum Doppler frequency of the spread clutter signal caused by FM ranging. The simulation and flight test results verify that the proposed clutter rejection frequency is the optimum value that can improve the detection capability of FM ranging airborne radar.