Radar system errors in polarization diversity measurements

The measurement capability of a polarization diversity radar is limited by several characteristics of the system and particularly by the performance of the antenna, which is characterized by the integrated cancellation ratio or integrated cross-polarization ratio. With reference to a transmitted or received signal of a desired polarization, these ratios describe the relative magnitude of the corresponding signal of opposite polarization generated as a result of antenna imperfections. In a single-receiver system operating with alternating horizontal and vertical polarization, the antenna performance tends to limit the accuracy with which the differential reflectivity can be measured. If the antenna pattern can be measured at orthogonal polarizations, then some of the bias introduced by antenna error can be removed from the resulting measurements. In this paper the magnitude of error of differential reflectivity relative to antenna performance is illustrated by calculations from theory. In a dual-receiver system, the antenna and microwave circuitry establish the minimum received power ratio, i.e., the minimum depolarization ratio, that can be measured by the radar. An increasing error component is introduced as the backscatter depolarization ratio approaches the system limit. As with the single-receiver system, antenna measurements can yield the relative amplitude and phase of the error signal, so that some of the bias due to antenna error can be removed in data processing. Observations by two dual-receiver radars in situations in which the backscatter depolarization ratio is less than the system limit are shown to illustrate the performance limits of these radars.