Signal cancellation phenomena in adaptive antennas: Causes and cures

TLDR

Conventional adaptive beamformers that minimize mean‑square error can suffer signal cancellation when adapting quickly, a phenomenon caused by the simultaneous reception of signal and interference and also observed in simple adaptive noise‑cancelling systems. The study of these effects in simpler systems is intended to shed light on analogous behavior in adaptive antennas. Two remedies have been proposed: Duvall’s approach removes signal components from the adaptive process and reinserts them afterward, while Widrow’s spatial‑dither technique shifts the array to modulate off‑look emissions, thereby preserving useful signals and curbing jammer effectiveness.

Abstract

Conventional adaptive beamformers utilizing some form of automatic minimization of mean square error exhibit signal cancellation phenomena when adapting rapidly. These effects result from adaptive interaction between signal and interference, when signal and interference are received simultaneously. Similar phenomena have been observed and analyzed in relatively simple adaptive noise cancelling systems. A study of these phenomena in the simpler systems is used to provide insight into similar behavior in adaptive antennas. A method for alleviating signal cancellation has been devised by Duvall, whereby the signal components are removed from the adaptive process, then reinserted to form the final system output. Widrow has devised a different solution to the problem: to move the receiving array spatially (or electronically) to modulate emanations received off the look direction, without distorting useful signals incident from the look direction. This approach is called "spatial dither" and introduces the additional possibility of modulating "smart" jammer signals, thereby limiting their effectiveness.