Abstract: 4. A system for reducing the effect of unwanted signals directed toward a receiver intended to receive reflected pulsed signals through an antenna having a radiation pattern that includes a desired main lobe and undesired additional areas, which includes: means for receiving said reflected pulsed signals; other means for receiving said unwanted signals; means for combining the outputs of both said receiving means in opposition; means periodically adjusting the output of one of said receiving means relative to the other to provide a minimum output of said combining means; and means holding constant the adjustment of said adjusting means between said periodic adjustments.