Clutter filtering and processing techniques for EMI detection and angle measurement in pulse Doppler radars

A pulse Doppler radar transmits a block of constant PRF and coherently phased RF pulses, referred to as a "coherent dwell interval" or CDI. The resulting radar echo pulses are treated as a single entity and coherently integrated in the Doppler filter bank in the radar's receiver/processor. This provides both coherent processing gain as well as the velocity discrimination capability necessary to detect small targets in a cluttered environment. The relatively long CDI and minimum antenna scan rate constraints generally restrict the target illumination to only several CDIs per beam dwell. With each CDIs echo power potentially modulated due to the RF frequency diversity between CDIs (to reduce target fading loss), there is little basis for improving the target bearing estimate by centroiding across the CDIs of the beam dwell. In addition, the entire Doppler filter bank output in any range cell can be corrupted by a single EMI pulse. This can not only mask a true target echo at that range but can be difficult to distinguish from one or more true target echoes. False alarms are the inevitable result. A filtering methodology is presented for optimally suppressing the clutter contained in the received CDIs, thereby revealing EMI pulses contained in the data as well as the antenna scan modulation on the target echo. Several algorithms are suggested to extract the EMI detection and target bearing estimate from this data.