مرکز منطقه ای اطلاع رساني علوم و فناوري

Abstract :

Several theorems are derived by using the reaction concept. They apply to single frequency sources of finite extent, and to fields which are finite and continuous on a hypothetical closed surface $S$ whose inside or outside is source-free. 1) The field on the source-free side of $S$ is uniquely determined by the normal components $E_{n}$ and $H_{n}$ on $S$ . 2) For measurements on the source-free side of $S$ , the primary source can be replaced by any of the following secondary sources on $S$ : (a) Normal electric and magnetic dipoles in free space. (b) Normal electric and magnetic quadrupoles backed by a medium which makes $E_{n} = 0$ and $H_{n} = 0$ . (c) A certain combination of electric and magnetic normal dipoles and quadrupoles which gives zero field on the source side of $S$ . The prescription for (a) requires the solution for the field of the primary source when it is inside a cavity on whose walls $E_{n} = 0$ and $H_{n} = 0$ . The surface densities of the various components of secondary sources (b) and (c) are given in terms of the free-space primary field. The formulas are comparatively simple when $S$ is plane. Many applications are cited including a combination of multipoles, consisting of vertical electric and magnetic dipoles, which is equivalent to a horizontal electric dipole.

Keywords :

Antennas; Electromagnetic analysis; Aerospace electronics; Aircraft; Dipole antennas; Electric variables measurement; Extraterrestrial measurements; Frequency measurement; Magnetic field measurement; Magnetic separation; Optical surface waves; Poles and zeros;