The earlier phenomenological descriptions of the propagation of signals in inhomogeneous media — except the mirror-type, scattering-type descriptions — have an inherent misunderstanding and therefore these methods are wrong except the non-coupled WKB approximation. The cause of the problem is the wrong physical concept about the structure of the signals propagating in inhomogeneous media. Using a better physical concept of the signal structure propagating in inhomogeneous media and the method of inhomogeneous basic modes (MIBM) it was possible to derive correct full-wave solutions for propagating signals. The investigated example is a monochromatic plane wave propagating in an isotropic, inhomogeneous, linear media parallel to the gradient of the one-dimensional inhomogeneity. However, a generalization of the process for more complex inhomogeneities is possible.