Rain depolarization scatter prediction

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Virginia Polytechnic Institute and State University

This paper extends an existing mathematical model of rain depolarization and attenuation to include the expected variances as well as the usually predicted mean values. It emphasizes depolarization and develops data for waves with frequencies ranging from 4 to 34.8 GHz propagating in rain cells which vary in intensity from light to severe. General causes of output scatter are included, and the scatter induced by the rain drop size distribution is examined in detail. Predicted cross polarization variances in excess of 9 dB for certain frequencies are shown. This variance is significant in that it can easily exceed system threshold criteria of mean value designs. Methods for extending the depolarization predictions to attenuation variances are discussed. The paper concludes with a brief examination of resonance encountered when drop diameters are multiples or submultiples of critical wavelengths. Conclusions drawn are applicable to polarization diversity design; multiple hop systems requiring frequency reuse and systems constrained to operate under fixed polarizations.