Ice Depolarization Research Articles

Measurements and Prediction of the Polarization-Dependent Properties of Rain and Ice Depolarization

Relationships between rain and ice attenuation and depolarization at 19 GHz have been determined for linear incident polarizations ± 4 and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\pm 8\deg</tex> from vertical. These relationships are based on measurements made using beacon transmissions from a COMSTAR satellite. A technique is used to bound depolarization magnitude at any incident polarization from a depolarization magnitude measurement made at another polarization. This technique makes use of previous observations that depolarization is minimal at vertical and horizontal incident polarizations. The bounds are compared with the results from the COMSTAR measurements.

Ice depolarization at 11.7 and 19 GHZ on slant paths in Virginia, USA

Measurements of attenuation and cross-polarization on slant paths from theCtsandComstarD2 satellites to Blacksburg, VA, have been in progress for three years. The data for 1977 and 1978 have been analyzed to determine the extent of severe ice depolarization on these paths, and a number of events have been identified. The behaviour of the observed cross-polarization at 11.7 and 19 GHz in two events has been compared with current theory for ice depolarization.

Ice depolarization statistics for 19-GHz satellite-to-earth propagation

Observations were made at 19 GHz of depolarization due to ice crystals along a satellite-earth path with a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">38.6\deg</tex> elevation angle. The one-year data base included sufficient information to determine depolarization for any incident polarization angle. Depolarization was often observed in the absence of significant rain-produced copolarized signal attenuation. This depolarization is caused by ice crystals whose symmetry axes, as observed in the plane perpendicular to the direction of propagation, were usually within <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5\deg</tex> of vertical and horizontal. Maximum depolarization was observed for <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">45\deg</tex> linear or circular polarizations, and never exceeded -16 dB. For vertical and horizontal incident polarizations 8-10-dB lower maximum depolarization values were observed. Depolarization due to ice was also observed during most rain attenuation events. The unknown differential phase characteristics of rain-produced depolarization prevent further exact analysis of this ice depolarization.

Characteristics of rain and ice depolarization for a 19- and 28-GHz propagation path from a Comstar satellite

Relationships between rain and ice attenuation and depolarization for several incident polarizations have been determined experimentally for the first time. The relationships are based on measurements made using 19- and 28-GHz beacon transmissions from a Comstar satellite. Vertical and horizontal incident polarizations experience much less depolarization on the average than circular polarization or linear polarization incident at 45\deg . The measurements confirm that the usual orientations of the major symmetry axes of nonspherical raindrops and ice crystals are nearly horizontal. Joint cumulative distributions of attenuation and depolarization for one year of continuous measurement at 19 and 28 GHz are also presented. These distributions are useful for determining joint attenuation and depolarization margins required to meet outage objectives of specific satellite communication systems. For example, the outage of a 19-GHz dual-polarized system received with a polarization angle 21\deg from horizontal and having an attenuation margin of 20 dB would be depolarization-dominated unless the system could also tolerate at least -15-dB depolarization.

Ice-crystal depolarisation on satellite—earth microwave radio paths

This paper reviews the experimental measurement of crosspolarisation on satellite-earth paths, describes the identification of previously unexpected depolarisation by ice crystals, and outlines the theoretical explanations of ice depolarisation which have been reported in the literature. It summarises what is known, and what is not yet understood, about ice-crystal depolarisation. The paper discusses the implications of ice-crystal depolarisation for satellite communications system design.