Adaptive antenna systems
Proceedings of the IEEE
Abstruct-A system CoIlSisting of an antenna array and an adaptive processor CM perfonn filtering in both the space and the frequency domrirs, thm reducing the seafitivity of the signal-receiving system to interfering directionnl wise sources. Variable weights of a signal processor can be automatically adjusted by a simple adaptive tedmiqpe based on the least-mean-squares (LMS) algorithm. During the adaptive process an injected pilot signal simulates a received signal from a desired "look"
... ion. This allows the array to be "trained" so that its directivity pattern has a main lobe m the previolsly specified look direction. At the same lime, the array processing system can reject any incident noises, whose directiols of propagation are difierent from the desired look direction, by forming appropriate nulls in the antenna directivity pattern. The array adapts itsetf to form a main lobe, with its d i r h and bandwidth determined by the pilot signal, and to rejest signals OT wises occnrringolltsidethemainlobe~wellnspossibleintheminimmnmennsquare error sense. Several examples illustrate the convergence of the LMS adaptation procedure toward the correspoading Wiener optimmn solutiom. Rates of adaptation and &adjustments of the SdntMaS are predicted theoretially and checked experimentally. substaotial reductiom in noise reception are demonstrated in computer-simulpted experiments The techniques described are applicable to signal-receiving arrays for use over a wide range of frequencies.