Abstract: In an AMTI radar of the type in which the difference between the phase of a current radar return signal and the phase of a radar return signal in a corresponding range bin of a preceding pulse repetition interval (PRI) is averaged over a number of range bins in the range vicinity of the current range bin, phase differences for current range bins are determined as being clutter-like or non-clutter-like by comparison with the previously-determined average phase difference by means of a rectangular distance discriminator which compares the normalized in-phase and quadrature components (cosine and sine, respectively) of the current phase difference with the normalized in-phase and quadrature components of the average phase difference in a rectangular distance discriminator. The rectangular distance discriminator sums the absolute values of the in-phase difference and the quadrature difference and compares them against a rectangular distance discriminant, which in a preferred embodiment is unity.