Abstract
It is known that the Poynting vector in a plane electromagnetic field is always along its propagation direction irrespective of its polarization state. Here we show, by making use of a superposition of four linearly-polarized plane waves, that the Poynting vector in a non-paraxial field is dependent on its polarization state. This is theoretically explained by resorting to the so-called Stratton vector. An expression for the Poynting vector in terms of generalized polarization bases as well as polarization ellipticity is given, which is further extended to a non-paraxial field of continuously-distributed angular spectrum. The expression is the same as what was given very recently by Fernandez-Guasti for electromagnetic fields constructed on the basis of Heaviside–Larmor symmetry.