An adaptive radar apparatus (10) for substantially reducing background clutter, particularly relatively time-invariant clutter, such as sea clutter, and especially at low radar grazing angles. The apparatus (10) includes a transmitting antenna (12) having horizontally and vertically oriented, transmitting elements (26, 28) and a relative phase control therebetween and a receiving antenna (14) also with horizontally and vertically oriented receiving elements (30, 32) also having relative phase detection and phase shift possible therebetween. A controllable radar signal generator (16) is provided for supplying signals to the transmitting antenna (12) and a controllable signal processor (18) is provided for processing return signals from the receiving antenna (14). Means (20) are included for determining, from return test signals, a background mean null polarization for a number of radar range and azimuth cells and for providing null polarization control signals Ho, Vo and oo, to the signal generator (16) and return signal processor (18) to cause the radar to operate at a polarization state which is the same as the clutter mean null polarization. A corresponding method is provided for reducing background clutter, especially relatively time-invariant sea clutter, in low grazing angle radar.