  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
is also investigated. There exists an optimal current distribution that
minimizes the radiation Q for specified antenna geometry. The optimized Q and
the optimal current distribution may be determined by solving a generalized
eigenvalue equation obtained from the Rayleigh quotient for the radiation Q.
