Problems associated with correlation-loop adaptive antennas employing hard limiting

There are many applications of adaptive antennas where it is desirable to set an adjustable threshold below which received signals are not nulled by the adaptive process. This may be achieved with a gradient descent adaptive control algorithm by a suitable choice of integration loss and update gain factors. Generally, the gradient estimate is obtained by a correlation process, and the hardware design can be simplified by incorporating some form of signal limiting prior to the correlator. However, it is known that this can also have severe implications on the thresholding performance in the presence of multiple signals. The paper presents a straightforward discussion of the problems associated with the use of limiting and analyses the resultant degradation of the nulling characteristics of the array.