Array signal processing

Abstract

Array signal processing (ASP) represents a class of antenna system where the output from an array is subjected to various forms of signal processing (e.g. phase and amplitude control, time delay or frequency translation) in order to produce outputs which can simultaneously provide angular information relating to several different directions. A different aspect of ASP which has received considerable attention over the last few years is adaptive arrays and null steering antennas. Here, instead of defining a number of wanted directions for receiving signals we can specify some wanted and some unwanted directions; the latter may contain high-level interfering signals which must be minimised by means of directional nulls in the patterns. In some cases the directions of these nulls may be fixed or pre-programmed, but in many cases the antenna response must be adaptive. This means that the shape of the directional pattern is determined in response to the angular distribution of received signals in order to try to meet some desirable criterion. The simplest form of adaptive and null steering antenna is probably the sidelobe canceller. This can steer a single directional null within the sidelobe region of a normal directional pattern. Multiple null adaptive arrays in general define a 'wanted direction' and then introduce one or more feedback controls to minimise the signals from all other directions. Null steering systems have applications in radar, sonar and communication systems. In the latter case, there may be additional complications if it is not possible to specify the direction of the wanted signals.