In the paper we investigate one aspect of the validity of models currently used to calculate rainscatter interference in radio and satellite communication systems. Exact bistatic scattering cross-sections from spheroidal shaped raindrops are compared with those obtained from spheroids in the Rayleigh approximation and from spheres using the Mie theory at 11.7, 20 and 30 GHz. Comparisons are also made between bistatic radar reflectivities for rain populations at these frequencies. It is found that both the Rayleigh and Mie (sphere) approximations to the spheroidal raindrop yield errors in the bistatic scattering reflectivities. These errors can be significant in the case of the Rayleigh theory, but the Mie theory, in general, yields much closer results to the exact.