Airborne MTI via digital filtering

Clutter suppression for radar on moving platforms such as aircraft is basically a two-dimensional filtering problem. As target echo signals are a function of two parameters (azimuth and Doppler frequency), a clutter filter should operate in both of these dimensions. In Reference 6, a suboptimum approximation to the maximum-likelihood test, based on the space-time covariance matrix between the sensors of an array antenna and all the received echo pulses, has been described. This method works for arbitrary sensor configurations and staggered pulses. In this paper, a new method based on an equispaced linear array in flight direction is discussed. The special properties of such a line array lead to a very simple but efficient clutter filter with real-time capability. The inverse clutter filter can be used as an output for SAR imaging with increased SNR. In conclusion, a radar receiver with combined AMTI and SAR performance is suggested.