TABLE OF CONTENTS The key capability of adaptive interference nulling was developed for an intermediate frequency (IF) radar sidelobe canceller as represented by the patent of Howells [1]. An analysis of this approach by Applebaum [2] established the control-law theory governing the operation of an adaptive control loop for each array element. The Applebaum algorithm maximizes a generalized SNR with the assumptions that the desired signal is absent most of the time (as in a pulsed radar or sonar system) and the direction of arrival of the desired signal is known. Because the Howells-Applebaum processor is practical to implement, it has been applied extensively to the problem of clutter and interference rejection in radar systems [3] [6]. Unless otherwise noted, the analysis of the maximum SNR processor and illustrative examples given here follow the treatment of this subject given by Gabriel [7].
In introducing the Howells-Applebaum maximum SNR adaptive processor, it will be useful to discuss first the prerequisites of phase conjugacy, cross-correlation interferometers, and an RC integrator filter. With these introductory concepts in hand, the analysis of a simple two-element array having a single analog adaptive loop may then proceed. By studying this simple single-loop system behavior, a good perspective on adaptive system performance can be gained, since it is relatively easy to keep track of the various parameters affecting performance. For tutorial purposes analog circuits are utilized in the discussion, but digital processing is often preferred over analog processing in sophisticated systems.
Spatial filtering is...
