While direction finding for navigation purposes is becoming less important, there is a growing demand for determining the location of emitters as the mobility of communications equipment increases. The importance of direction finding lies in the fact that spread-spectrum techniques are increasingly used for wireless communications. This means that the spectral components can only be allocated to a specific emitter if the direction is known. Direction finding is therefore an indispensable first step in radio-detection, particularly since reading the contents of such emissions is usually impossible. Download the full paper for an introduction to the theory of direction finding.