Excitation of Orthogonal Radiation States

A technique for designing antenna excitation realizing orthogonal states is presented. It is shown that a symmetric antenna geometry is required in order to achieve orthogonality with respect to all physical quantities. A maximal number of achievable orthogonal states and a minimal number of ports required to excite them are rigorously determined from the knowledge of an antenna's symmetries. The number of states and the number of ports are summarized for commonly used point groups (a rectangle, a square, and so on). The theory is applied to an example of a rectangular rim where the positions of ports providing the best total active reflection coefficient, an important metric in multiport systems, are determined. The described technique can easily be implemented in existing solvers based on integral equations.