Stored Energies and Radiation Q

This paper discusses the methods for evaluating the stored electromagnetic energies and the radiation Q for an arbitrary lossless antenna. New expressions for the stored electromagnetic energies are derived by using the Poynting theorem in the complex frequency domain, and they are compared with previous theory and are validated by numerical examples. The minimization of radiation Q for small antenna is also investigated. There exists an optimal current distribution that minimizes the radiation Q for specified small antenna geometry. The optimized Q and the optimal current distribution for small antenna may be determined by solving a generalized eigenvalue equation obtained from the Rayleigh quotient for the radiation Q.