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. Klemm (see ibid., vol.34, no.3, p.269, 1987) proposed 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. This method works for arbitrary sensor configurations and staggered pulses. In this paper, a new method based on an equispaced linear array in the 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.