ABSTRACT
A. Historical Background The general problem addressed in this work is that of locating the sources of radiated energy received by an array of spatially distributed collectors, or sensors. It was, in fact, the desire to locate and track enemy aircraft using radar that gave birth to statistical signal processing as a subdiscipline of electrical engineering in the 1940s. In this early application, the parameters of interest were the direction, range, and radial velocity (doppler) of the target, all of which were to be estimated from the outputs of a single radar antenna. The direction to the target was the most important parameter to be estimated, since it had to be known before range and velocity could be determined. Target direction was usually determined by placing a collimating dish behind the antenna, sweeping the entire device through all possible target directions, and then finding the directions from which maximum energy was received. This simple system has been modified and refined over the years, and sophisticated algorithms have been developed to enhance radar direction-finding performance.
