The electromagnetic wave is one of the most important tools of a space scientist. The understanding of this tool is vital in our quest to extend our knowledge about space and the physics of space. This thesis deals with electromagnetic waves, their properties and the possibilities to use them in the field of space science. The topics are selected, such that they are relevant for the STEREO mission, which was launched in October 2006. Electromagnetic waves, in general, are discussed, with special emphasis on direction finding. At last, one of the methods for finding the effective length vectors, the numerical method, is treated with regard to the STEREO spacecraft.