Power of a simple electric multipole of finite size

摘要

A simple electric multipole of finite size in the form of a spherical current sheet with a surface current density in the theta direction varying as sin 2theta is considered. The electromagnetic fields outside the spherical surface are of the same form as that of the corresponding point electric multipole situated at the origin and oriented in the z direction. The power is separated into the radiative and the reactive parts and compared with the separation made on the basis of propagating and evanescent waves. The evanescent waves contribute only to the reactive power, and the propagating waves contribute to both the radiative and the reactive powers. The power flux density is also separated into the real and the reactive parts, and the characteristics of the two parts of the power flux density are discussed.