A clutter rejection digital filter for a pulse doppler radar

Includes bibliographical references (pages 41-42)In airborne or shipborne doppler radar, discrimination of moving target echos from stationary clutter echo is complicated by the doppler frequency shift of the stationary clutter echo due to the radar's own motion. When a severe clutter interference is expected, a specially designed doppler filter is needed to reject as much of the clutter as possible while enhancing the echo signal from a moving target. For this purpose, the optimum Moving Target Indication filter is described and a FORTRAN program to calculate the filter weights is presented. The frequency response of certain calculated filters is also analyzed. To implement these filters in a radar system, the optimum weights must be truncated to fit the finite word length of the radar's computer. The effect of truncation is analyzed for various degrees of truncation and various filter bandwidths. The filter's truncation errors are found to be within a tolerable limit for a typical level of truncation (sic.). If more than one set of filter weights can be stored in the radar's computer, the computer may be able to choose a set of weights based on information about the radar's own motion. A simple method of implementing the adaptive doppler filter by the method of variable filter weights is suggested