Rain-induced deflection of microwave and millimetre-wave radiowaves

A model is developed to describe the angular deflection of the propagation vector of a radiowave propagated through a rain-filled medium. This additional effect occurs in a similar way to the manner in which raindrops canted in a plane perpendicular to the propagation direction cause rotation of the plane of polarisation, owing to differential attenuation and phase of components along the raindrops´ principal axes. It is shown that the presence of raindrops with symmetry axes inclined to the propagation path and in the plane of polarisation produces a differential attenuation of the field components, resulting in a rotation of the propagation vector towards a direction perpendicular to the minor raindrop axis. Maximum deflection angles are given for several frequencies between 11 and 30 GHz and rain rates up to 150 mm/h. Some practical consequences of deflection are discussed.