Evaluation of antenna Q

A method is presented for evaluating the
Q
of an antenna, where the
Q
is defined as in conventional network theory. The method consists of subtracting the energy density associated with the power flow from the total energy density, thus enabling the magnetic and electric reactive energy to be computed. Specific application of the method is made to the evaluation of the
Q
of spherical and cylindrical modes. It is verified that the
Q
becomes very large when the order of the mode exceeds
k_{0}a
where
a
is the radius of the sphere or cylinder on which the sources are located.