Signal cancellation phenomena in adaptive antennas: Causes and cures

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 modnlate 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.

Finite Data Performance Analysis of LCMV Antenna Array Beamformers With and Without Signal Blocking

“…To see the details about the effect of the signal blocking on P io and P no of (48), we consider the following B used by the Duvall beamformer [4]:…”

“…The signal blocking technique was originally proposed by Widrow et al [4] to tackle the coherent problem. Due to its effectiveness, the idea of removing the desired signal before computing the weights has been widely applied for antenna array beamforming [5][6][7][8][9][10].…”

Beamforming With a Maximum Negentropy Criterion

“…Hence, in adjusting the active weight vector of the GSC to provide a signal with the highest possible negentropy, we hope to remove or suppress noise and reverberation. As we will demonstrate, the maximum negentropy (MN) beamformer can achieve this goal without the signal cancellation problem encountered in conventional beamforming algorithms [5]. Moreover, our technique can circumvent the permutation and scaling ambiguity problems by maintaining a distortionless constraint in the look direction.…”

“…The blocking matrix is usually constructed in order to keep a distortionless constraint for the signal filtered with the quiescent vector. Subject to this constraint, the total output power of the beamformer is minimized through the adjustment of an active weight vector, which effectively places a null on any source of interference, but can also lead to undesirable signal cancellation [5]. To avoid the latter, many algorithms have been developed.…”

Study of beamforming techniques for ultrasound imaging in nondestructive testing

“…Shan and colleagues [29] introduced a new on-line adaptive array beamformer capable of working well even when the desired signal and interferers are coherent. Widrow and colleagues [30] suggested that coherent interference could be eliminated by movement of the sensor array via what is referred to as the "Duvall" beamformer and the "Spatial Dither" algorithm. An electronic version of that suggested technique was then presented [29], and was especially appropriate for fixed sensor structures.…”