In a tracking radar system target glint and multipath sometimes produce signals which falsely indicate high acceleration rates of the target. These signals cause the boresight of the antenna to be driven away from the direction in which the target actually lies.To avoid this problem, received signals from a receiver are fed through a switch which is opened whenever the target appears to have an acceleration or velocity above a threshold value. The threshold value is varied so that the proportion of the time during which the switch is open is kept approximately constant. Thus, if there is a period during which a large number of high acceleration or high velocity signals appear from the receiver (for example is there is a very high noise level) the switch still remains closed for a certain proportion of the time period. This ensures that the tracking system never loses the target while also ensuring that false tracking due to target glint and multipath is minimized.A circuit is included so that, when the switch is open the antenna is not brought to a complete halt but rather is allowed to continue to move in the direction that it was moving before the switch was operated.