On the reactive energy of an aperture

A novel expression for the reactive power of a planar antenna is given in the form of the difference of two positive integrals, depending, respectively, only on the TE and TM parts of the field with respect to the direction orthogonal to the aperture. The expressions for the inductive and capacitive powers recently given by Rhodes are then compared with the new results, and it is shown that these expressions identically contain the same positive term (which therefore must cancel).