Forward‐Scattering Theorem in Antenna Theory

This chapter discusses the forward‐scattering theorem concerning the N ‐port receiving antenna system. The antenna system is placed in the linear, homogeneous, and isotropic embedding whose electromagnetic properties are described by real‐valued and positive constants ɛ
₀
and μ
₀
. The presence of the antenna system is accounted for via the scattered EM wave field. Accordingly, the incident field can be interpreted as the EM field that would exist in the problem configuration if there were no antenna system. The theorem relates the sum of the scattered and absorbed power by the receiving antenna system to the scattered far‐field amplitude observed in the direction of propagation of the incident plane wave. Furthermore, the reciprocity theorem of the time‐correlation type is applied to the unbounded domain exterior to the antenna system and to the scattered field state. The chapter explains the antenna forward‐scattering theorem in the time domain.