Centers of structures in electromagnetism--a critical analysis

Some principles for finding reference points or centers of structures in electromagnetism are outlined. It is pointed out that the centers which are found depend on arbitrary choices. Since some of the principles are based on Friis´s transmission formula and the radar equation, these are given in forms suitable for finding centers. The use of correction factors and near-field parameters are outlined. In particular, proper use of different near-field radar cross sections for plates and spheres are outlined.