B.S.T.J. Briefs: Rain-Induced Differential Attenuation and Differential Phase Shift at Microwave Frequencies

Rain-Induced Differential Attenuation and Differential Phase Shift at Microwave Frequencies By J. A. MORRISON, M. J. CROSS, and T. S. CHU (Manuscript received January 15, 1973) We give calculated results of differential attenuation and differential phase shift caused by rain, based on scattering of a plane electromagnetic wave by horizontally disposed oblate spheroidal raindrops. Two polarizations of the incident wave are considered, as depicted in Fig. 1. The factor e~iwt has been suppressed. Subscripts I and II designate electric fields parallel and perpendicular to the plane containing the axis of symmetry of the raindrop and the direction of propagation of the incident wave, respectively. The angle between the direction of propagation and the axis of symmetry is denoted by a. For terrestrial microwave relay systems we take a = ir/2, but for satellite systems other values of a are of interest. The incident wave induces a transmitted field in the interior of the raindrop, and a scattered field. In the far field the quantities of primary interest are the complex forward scattering functions1 &i(0) and S I I ( O ) . For the two polarizations considered, the polarization of the far scattered field is the same as that of the incident wave. However, when oblate raindrops are canted with respect to the vertical, the vertical and horizontal polarizations commonly used in radio communications systems will be neither of the two aforementioned polarizations. Then cross-polarization coupling will occur as a result of the difference between Si(0) and Sn(0).