An analytical model based on the theory of the radiative energy transfer (RET) is used to predict the bistatic scattering pattern of single trees. A set of propagation measurements were designed and carried out at micro- and millimeter wave frequencies to characterise the re-radiation functions of single trees modelled by simpler scattering functions, which may be predicted qualitatively from the RET theory. The implementation of this deterministic approach gives a good understanding of the propagation mechanisms. The frequency dependence of the scattering function with tree characteristics in full leaf are presented and results at 20 GHz are compared with results at 62.4 GHz.